Impact of acute exercise on performance and physiological stress during simulated firefighter occupational tasks

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Bordonie, Ann M. Robbins, Parker L. Jones, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4547891/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 30 Nov, 2024 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract Purpose We aimed to determine how a bout of resistance or aerobic exercise impacts physiological responses and performance during firefighting occupational tasks. Methods Thirty-two non-firefighters completed two baseline assessments, and three trials: resistance exercise (RE), aerobic exercise (AE), or rested control (CON). Trials were followed by an occupational task assessment (OTA; four rounds of 10 deadlifts (85 or 135lbs) and 0.15-mile 40lb-sandbag carry) in an environmental chamber (35°C/50% humidity). Results Time to complete by condition was not statistically different (CON: 1134 ± 261, AE: 1198 ± 214, RE: 1212 ± 302 sec; p = 0.162). Average heart rate (CON: 148.5 ± 16.2, AE: 166.3 ± 11.5, RE: 159.9 ± 13.0 bpm; p < 0.01), core temperature (CON: 37.56 ± 0.35, AE: 38.68 ± 0.26, RE: 38.44 ± 0.46°C; p < 0.01), and skin temperature (CON: 36.33 ± 0.54, AE: 37.48 ± 0.58, RE: 36.87 ± 0.86°C; p < 0.01) were elevated during OTA following AE and RE compared to CON, and higher following AE compared to RE. Conclusion Our findings suggest job performance may not be impacted, physiological strain during the tasks may be elevated; increasing risk for heat injury following on-shift exercise, and more prominently following aerobic exercise. Biological sciences/Physiology Health sciences/Health occupations Environmental Stress Occupational Stress Fire Services Strength Training Endurance Training HIIT Figures Figure 1 Figure 2 Figure 3 Figure 4 1 INTRODUCTION Firefighters are exposed to a broad spectrum of environments typically divided into two types: fireground (vehicle fires, wildfires, structural fires) and non-fireground (medical emergencies, vehicle accidents, natural disasters). Both can present a risk for heat stress ranging from hot summer temperatures upwards of 32°C, with wildland fire suppression reaching 78°C [ 1 ] and structural fires reaching extreme temperatures of 300°C [ 2 ]. Personal protective equipment (PPE) worn to protect firefighters from extreme heat weighs approximately 17–25 kg [ 3 , 4 ]. This added weight and restricted movement can exacerbate the stress imposed on the firefighters and limit occupational performance [ 3 , 5 , 6 ]. These high levels of physical and environmental stress imposed on firefighters reinforce the need for fitness training opportunities and physical fitness standards. A study looking at the adaptations to fire academy training saw significant improvements in fitness during academy training that were subsequently lost when reassessed following firefighters’ probationary period (8 months later). This included declines in body composition, aerobic capacity, muscular strength, and muscular endurance, suggesting overall health and fitness declined once firefighters left the academy [ 7 ]. A National Fire Prevention Association (NFPA) report notes that 70% of firefighters do not meet recommended health and fitness guidelines [ 8 ]. This raises concern as research suggests poor fitness and lack of a well-designed training program decrease occupational performance and increase firefighters’ risk for overexertion injuries [ 9 , 10 ] and increase cardiovascular disease/event risk [ 11 – 13 ]. Research on exercise interventions in firefighters has revealed promising improvements in occupationally relevant fitness parameters, including general health outcomes [ 14 – 17 ] and occupational performance [ 18 ]. However, only 27% of fire departments across the United States provide health and fitness programs [ 8 ]. Research has shown that firefighters who participated in on-shift (within the station) physical activity accumulated a higher level of total physical activity on a weekly basis and had better cardiovascular health indicators over those that do not [ 15 ]. The importance of maintaining physical fitness despite the hectic work schedule makes it crucial that firefighters are provided time to exercise while on shift. However, it is important to consider the cumulative exertional stress this could impose. Current literature indicates physiological measures (i.e., heart rate, skin temperature, ventilation, and core temperature) are intensified when performing simulated firefighting tasks [ 19 – 24 ]. Core temperature, heart rate, lactate concentrations, and workload are all increased in heated environments [ 25 – 27 ]. Firefighters have expressed uncertainty about adding the physiological stress of on-shift exercise to the stress of their daily job tasks [ 28 – 30 ], concerned the added stress response may lead to decrements in occupational performance. Two studies have investigated the effects of exercise training-induced fatigue on simulated firefighting tasks and the physiological stress experienced after a bout of acute exercise. They reported a 9.6% [ 31 ] and 45% [ 32 ] increase in time to complete 10-minutes after acute exercise and a 9.8% increase in time to complete 60 minutes after exercise [ 32 ]. These studies suggests that a single on-shift exercise session may transiently impair the ability to meet occupational requirements. While one of these studies used circuit style training and the other involved high-intensity resistance training, no study to our knowledge has directly compared the acute impact of resistance training and aerobic endurance training on the physiological readiness of firefighters. Therefore, the purpose of this study was to investigate the impact of resistance and aerobic endurance exercise on physiological outcomes and performance related to firefighter occupational performance. We hypothesized that aerobic exercise would have a greater impact on occupational performance compared to resistance training, by increasing time to complete and markers of physiological strain and fatigue (heart rate, skin temperature, ventilation, core temperature, and blood lactate concentrations). A secondary aim was to determine if the acute exercise bouts impair the rate at which the physiological variables recover following occupational task performance. We hypothesized that aerobic exercise would result in a slower rate of recovery following occupational task recovery compared to resistance training. 2 METHODS 2.1 Study Design This study utilized a repeated measures quasi-randomized control trial. Participants were local members of the community rather than firefighters. This decision was made in order to obtain an adequate sample size for the statistical analysis. Each participant completed a series of baseline assessments for cognitive, physiological, aerobic, and anaerobic performance outcome measures as a part of the larger study that was approved by the Institutional Review Board at Auburn University (IRB protocol code #22–479 AR 2211, 05/05/2022). These baseline assessments have been outlined below as we will utilize values to quantify the fitness level of the population. Participants then completed three exercise sessions in quasi-randomized order: 1) resistance exercise (RE); 2) aerobic high-intensity interval training (AE); or 3) rested control (CON). Each exercise session was directly followed by an occupational task assessment (OTA). A seven-day wash-out period was included between trials to reduce the risk of residual fatigue impacting subsequent trial performance. Participants completed the CON condition second to reduce the number of potential unique trial order group comparisons. Block randomization of trial order of exercise type was generated in Microsoft® Excel (Microsoft Corporations, Redmond, WA USA) by a co-investigator and reported allocations to the lead author (PA). Independent variables included Pre-OTA condition (AE, RE, CON). The primary dependent variable was OTA time to complete, with secondary dependent variables including core temperature, blood lactate concentrations (BLC), skin temperature, heart rate, and ventilatory rate. 2.2 Participants Forty-one individuals were enrolled in the study. Thirty-two (15 males, 17 females) participants completed all study requirements (25.19 ± 4.12 yrs., 173.78 ± 9.84 cm, 75.57 ± 13.22 kg, 23.28 ± 7.43% body fat). All participants were individuals from the local community, none of which were current firefighters. Additionally, all participants met the following inclusion criteria: (i) 19–45 years of age, (ii) free of musculoskeletal injury, (iii) available to complete the full 5-week study timeline, (iv) comfortable carrying out exercise tasks while in a heat chamber, (v) agreed to adhere to study requirements, and (vi) passed a health screening. Participants were excluded if they: (i) had a known medical condition, physical or psychological condition, preventing participation in exercise, (ii) had a current musculoskeletal injury or were rehabilitating from a recent one, (iii) had been diagnosed with asthma (defined as experienced symptoms, or prescribed any form of treatment within the past 4 years), (iv) had a history of heart condition or high blood pressure, (v) experienced pain in chest at rest, during activities of daily living, or when performing physical activity or exercise, (vi) had been prescribed medically supervised physical activity only by a primary care physician, or (vii) had recently experienced a heat related illness or injury (i.e., heat exhaustion, heat stroke, etc.). Informed consent was obtained by lead author (PA) prior to enrollment in the study. No interested participants were excluded. Out of the forty-one enrolled, five participants withdrew due to scheduling conflicts, three withdrew due to difficulty, one was withdrawn for not adhering to study protocols. 2.3 Procedures All study procedures occurred in the School of Kinesiology buildings starting in January of 2023 and ending in August of 2023 when appropriate power was obtained. Each participant completed a baseline fitness assessment (Day A and B) prior to completing the acute exercise trials (Trials 1–3). Participants were asked to refrain from caffeine and recent exercise for 24 hours leading up to Day A and Day B. Adequate hydration (USG < 1.02) of each participant was assessed before testing on Day A and Day B. The urine sample was analyzed with a refractometer (V-Resourcing, Hunan, China) for hydration status. If the participant was dehydrated (USG = > 1.02), they were provided 16 oz of water to drink and provided a new urine sample. All participants were adequately hydrated before they began baseline testing. Participants were encouraged to schedule visits at the same time of day and maintain a consistent diet during the duration of the study, however, this was not controlled. 2.3.1 Day A (Body Composition and Aerobic Fitness) Body composition (fat, muscle, and bone mineral density) was measured with a full-body dual-energy X-ray absorptiometry (DXA) scan (Lunar Prodigy; GE Healthcare, Chicago, IL, USA). Participant’s height and weight were obtained utilizing a digital scale and stadiometer (SECA, Hamburg, Germany). Peak oxygen consumption (VO 2 peak) was assessed as a measure of cardiorespiratory fitness level utilizing a modified Bruce protocol [ 33 ] for treadmill (Woodway, Waukesha, WI, USA) graded exercise testing. Participants were asked to give their best effort and continue until they could go no longer. The test was terminated once participants reached volitional fatigue. VO 2 peak was determined as the maximal oxygen consumption achieved during the test. Respiratory exchange ratio (RER > 1.15), HRmax (within 10 bpm of age-predicted max), BLC (> 8.0 mM), and volitional fatigue, were utilized to verify a valid maximal effort was given by the participant. Additionally, lactate threshold was estimated as part of the larger study. The participant’s fingertips were disinfected using an alcohol wipe and dried with a gauze pad. Once dried, a fingerstick was administered using a BD Microtainer ® auto-lancet (BD, Franklin Lakes, NJ USA) to draw a drop of blood from the participant’s fingertip. The first drop was wiped by the gauze pad and the second drop of blood was placed on the lactate test strip and inserted into the Nova Biomedical Lactate Plus Meter (Nova Biomedical, Waltham, MA USA) for measurement. The Lactate Plus Meter was calibrated bi-weekly during testing with low and high control solutions and the accuracy was confirmed to be within acceptable limits (i.e., low control solution: 1.0–1.6 mmol/L; high control solution: 4.0–5.4 mmol/L). 2.3.2 Day B (Muscular Strength, Power, and Familiarization) Participants completed a counter-movement vertical jump on a Leonardo Mechanograph force platform (Novotec Medical GmbH, Pforzheim, Germany) as an assessment of lower body muscular power. The participant stepped onto the platform and was instructed by the research team to jump as high as possible. This task was completed three times with a one-minute rest between attempts. Three repetition maximum testing (3RM) performance was used to determine training load during the acute resistance training session, as well as an indicator of muscular strength. The squat, bench press, and hex-bar deadlift movements were used to assess upper and lower body strength. During each attempt, participants were provided spotters. For the squat, the participants were asked to place the barbell and attached weights on the top of the shoulders behind the head and completed a full squat. If the participant’s back angle began to change on the repetition, it was not counted. For bench press, they started by laying on their back on a lifting bench setting five points of contact (head, shoulders, buttocks, and both feet flat on the floor). To complete the lift, the participant touched the bar to the chest (with a slight pause at the chest) and raised back up to the starting position. For the hex-bar deadlift, the participants lifted the weight bar from the ground, with both knees and hips bent while maintaining a constant back angle throughout. If the weight was hiked or slid up the thighs or their back angle changed, the repetition was not counted. The hex-bar deadlift was utilized to reduce technical errors and potential injury risk in inexperienced lifters [ 34 ]. The participants were monitored by a certified strength and conditioning specialist (author - P.A.) to ensure they performed each exercise completely and with proper form. Participants started the 3RM protocol by completing the lift with a series of warm-up lifts (45-lb bar for 8–10 reps, 50% of projected 1-RM for 6–8 reps, 75% for 3–5 reps, and 85% for 1–3 reps). Their first attempt was at 95% of self-reported 3RM. Each set included a minimum of two minutes of rest and a maximum of five minutes of rest. The maximum weight completed for three reps while maintaining good form was utilized to project 1RM based on the National Strength and Conditioning Association’s (NSCA) guidelines [ 35 ]. If participants only achieved one or two reps at attempted weight, that value was taken and utilized to project 1RM. During Day B, participants were also familiarized with the Occupational Task Assessment (OTA). They were instructed on how to don the standard firefighter PPE, including turn-out gear, gloves, boots, and a helmet. After which, they entered the chamber that was set at 35°C (95°F) with 50% relative humidity and practiced one round of the OTA to reduce any learning effect associated with the OTA. 2.5 Experimental Trials After the fitness assessments (Day A and B), the participants completed the acute exercise trials (Trials 1–3). Participants were asked to refrain from caffeine and exercise during the 24 hours leading up to each of the three trials. Participant hydration was tested before each trial. If the participant was dehydrated, they were provided with water to drink and provided a new urine sample for analysis. Each of the acute exercise sessions were lead and monitored by a certified strength and conditioning professional (P.J.A) and at least one other researcher. 2.5.1 Acute Exercise and Control Trials The full-body resistance exercise session was programmed utilizing NSCA guidelines for strength training [ 36 ]. Prior to starting the RE session, participants completed a structured warm-up. The warm-up protocol followed the NSCA’s recommended structure of a general and specific warm-up involving a moderate-paced walk on a treadmill [ 36 ] and dynamic movements that mimicked and prepared the participant for the movement patterns of the acute resistance exercises, including bodyweight squats, hip rotations, scapular protraction and retraction [ 36 ]. After the warm-up, participants completed four exercises emphasizing each major movement in the following order:1) back squat, 2) barbell bench press, 3) hex-bar deadlift, and 4) barbell bent-over rows. Participants completed three sets of six repetitions of each exercise at ~ 80% of their projected 1-RM from baseline testing with two minutes of rest between sets. If a participant was unable to complete a set at the prescribed weight, the weight was lowered until the set was finished and remained at that weight for subsequent sets. BLC measurements were taken pre- and post-exercise. Total exercise time varied between resistance session, due to variability in the number of warm-up sets needed based on working weight. The aerobic bout involved high-intensity interval training (HIIT). This exercise session was programmed utilizing NSCA guidelines for aerobic endurance training and a 2018 investigation of a cycling HIIT protocol [ 37 , 38 ]. Prior to starting the AE session, participants completed a structured warm-up. The warm-up protocol followed the NSCA’s recommended structure of a general warm-up, involving a moderate-paced walk (4.8 kph) on a treadmill [ 37 ]. Each participant completed five rounds of four minutes of low-intensity exercise at approximately 50% of heart rate reserve (HRR) and 30 seconds of high intensity at approximately 90% of HRR on a treadmill. The HRR values were calculated with the Karvonen method [ 39 ] utilizing resting and max heart rate values from the baseline assessments. BLC measurements were taken pre- and post-exercise. The aerobic exercise session was programmed to take approximately 27 minutes. A control session was completed to assess any effect of exercise in general, regardless of modality. This control session involved having participants sit in our laboratory in a quiet, controlled environment where they could work on their laptops, scroll on their phones, browse the internet, or read a book. However, participants were told to avoid any stressful or overstimulating work, and activities during the 30-minute time frame were recorded. The activity choices were decided in tandem with what the local Fire Department described as activities that firefighters typically partake in during their on-duty downtime. BLC measurements were taken pre- and post-control session. 2.5.2 Transition Period Participants then donned standard firefighting turnout gear and PPE as they would during a live emergency call. BLC was once again assessed prior to entering the environmental chamber where participants completed the simulated occupational task assessment. 2.5.3 Occupational Task Assessment (OTA) The environmental chamber conditions were set to 35°C (95°F) with 50% relative humidity to mimic temperatures experienced during highway extractions on a hot summer day, other outdoor emergencies, and salvage [ 40 , 41 ]. This temperature was chosen, rather than hotter temperatures, to replicate non-fireground scenarios known to constitute ~ 80% of firefighters' emergency calls in the southeastern United States [ 28 ]. Inside the chamber participants completed a series of tactically relevant physical exertion tasks involving repeated lift and carry and walking movements. A Rogue Fitness® sandbag (Rogue Fitness, Columbus, OH, USA) was loaded to either 135lbs or 85lbs. Firefighters frequently have to lift, drag, and carry objects of this size during emergency calls [ 42 ]. Participants utilized the 135lb sandbag if their 3-RM deadlift was greater than 175 lbs and deadlift to body weight ratio greater than 1.25. Those that did not meet these criteria used an 85lb sandbag. Participants completed 10 repeated sandbag deadlifts with the prescribed sandbag load. They then lifted a lighter Rogue Fitness® sandbag, loaded to 40lbs to mimic the average weight of a firehose, onto their shoulder and carried it while walking on a treadmill for 0.15 miles. These movements were completed in a circuit twice, before stopping to complete a cognitive assessment (part of the larger study). Participants then completed two additional rounds of the OTA. They were instructed to complete the tasks to the best of their ability and as quickly and safely as possible. Termination criteria included volitional fatigue. Additionally, for the safety of participants, they were removed from the environmental chamber if they reached a core temperature of 39.4°C. 2.5.4 Recovery Protocol Upon completion of the heat chamber protocol, participants were escorted out of the chamber and into an open area where they removed the helmet, gloves, and turnout jacket and sat in a chair. While recovering they were allowed to roll their pants down below their knees. Boots were kept on mimicking the procedures firefighters follow during emergency call recovery. Participants were provided one bottle of room temperature water to rehydrate. Heart rate, skin temperature, ventilatory rate, and core temperature were monitored continuously during the recovery period. BLC was assessed at immediate post-simulated firefighting, 5-, 10-, 20-, and 40-minute post-OTA. 2.6 Physiological Monitoring and Perceived Exertion Measurements Heart rate, ventilatory rate, skin temperature, and estimated core temperature were monitored in real-time to assess the physiological stress and intensity of response during the entirety of each trial utilizing the EQ02 + LifeMonitor (Equivital EQ02, Hidalgo, UK). A validated heart-rate-derived algorithm [ 43 , 44 ] is used by the Equivital Black Ghost software to estimate core temperature. This system has recently been shown as a valid alternative to gold-standard rectal temperature monitoring in similar environments and exercise conditions [ 45 ]. The Equivital measures skin temperature at the torso using an infrared temperature sensor on the back of the Equivital device, which is in contact with the individual's skin, under the individual's arm (at the mid-axillary line of the thorax in line with the individual's xiphoid process of the sternum). BLC was measured before and after AE, RE, CON, and OTA. BLC was also measured during recovery at 5-, 10-, 20-, 30-, and 40-minute timepoints. BLC measurements were obtained using the Nova Biomedical Lactate Plus Meter and procedures outlined above for lactate threshold testing during Day A. The OMNI 0–10 Rating of Perceived Exertion (RPE) scale was used during acute exercise, at the end of RE sets, at the end of both high and low intervals during AE, and the beginning and end of the control session. The Borg 6–20 RPE scale [ 46 ] was also collected after each OTA task (i.e., sandbag deadlifts and sandbag carry) and every five minutes during recovery. The OMNI scale was used during RE to correlate to the number of Reps in Reserve (RIR) [ 47 ] and provide an accurate training intensity. It was also used during AE, allowing comparisons with RE perceived exertion. However, the Borg scale was used during the OTA because of its correlation to heart rate [ 48 ]. 2.7 Statistical Analysis The Shapiro-Wilks Test, Q-Q plot inspection, and Mauchly’s Test was used to evaluate normality and sphericity respectively. First, we conducted a traditional repeated measures ANOVA comparing the total time to complete the OTA by condition. Then conducted an equivalence test for ANOVA to determine if the exercise conditions resulted in practically equivalent changes in time to complete OTA. A practical effect size to determine equivalence bounds was calculated based on the mean difference in time to complete OTA based on the recommendations of the local fire departments on the meaningful difference in time to complete the outlined tasks in an actual occupational scenario. This value was then divided by the pooled standard deviation of time to complete OTA from the actual data collected in this study to obtain a practical effect size, then converted to a partial eta squared (η2p) utilizing the equation provided below. Practical Effect Size Equation : Cohen’s d = M difference(estimated) /SD pooled(actual) ; Cohen’s f = d/2; η2p = f 2 /(1 + f 2 ) d = 180 sec/((301.62 sec + 214.23 sec + 261.23 sec)/3) ; f = (0.695/2); η2p = 0.348 2 /(1 + 0.348 2 ) The equivalence test was completed using the TOSTER package for R to compare the largest effect size observed between exercise conditions against a practical effect size of η2p = 0.11 (f = 1.382). Additional variables assessed to describe the physiological mechanisms behind performance changes included heart rate, core temperature, skin temperature, ventilatory rate, blood lactate concentration, and rating of perceived exertion (RPE). Average values were calculated based on the minute-to-minute values for heart rate, core temperature, skin temperature, and ventilatory rate during OTA and recovery. Additionally, the time to get to the environmental chamber and put on the firefighter gear (gear time) was compared between AE, RE, and CON to understand differences in the time taken from exercise to OTA. Four-minute averages were calculated for each of these variables for graphic representation and area under the curve (AUC) calculations. The AUC was used as a metric of cumulative heat strain experienced accounting for the maximum temperature reached and the time spent at elevated core temperatures. Five-minute change scores underwent trapezoidal summation to calculate the total AUC for both OTA and recovery. A repeated measures analysis of variance (ANOVA) was performed on average values for each of the measures to determine differences across conditions and recovery. Core temperature was the only peak value assessed due to its relation to exertional heat illness risk [ 49 ]. Other peak values were not assessed to reduce the risk of type I error from multiple testing. Equivalence tests were not used for variables other than time to complete because it is unclear what a practically significant difference for these physiological variables would be. For any significant main effects detected, post hoc comparisons with Bonferroni adjustments were utilized for multiple comparisons. If sphericity was violated, statistical interpretations were made utilizing Greenhouse-Geisser adjusted degrees of freedom. Data is expressed as mean ± standard deviation. Significance in this investigation was set a priori at a p-value ≤ 0.05 for all measurements. R Statistical Programming Software Version 4.1.2 (RStudio; Boston, MA) was used for all statistical analyses [ 50 ]. The application, G*Power, was utilized a priori to determine a sample size of 28 total participants necessary for a sufficiently powered study. To estimate sample size the following values were used: test family = F tests, repeated measures ANOVA, one group, three measurements, correlation among repeated measures = 0.5, non-sphericity correction ε = 1.0, α = 0.05, 1-β = 0.80, η2p = 0.06. Effect size classifications included a small effect (η2p = 0.010–0.059), moderate effect (η2p = 0.060–0.139), and large effect (η2p > 0.14). This effect size was determined based on previous research observing effect sizes from 0.01–0.56 with similar outcomes [ 31 , 32 ]. 3 RESULTS 3.1 Baseline Values Pre-trial USG (F(2, 62) = 0.752; p = 0.475, η2p = 0.02) and Pre-BLC (F(2, 62) = 0.281; p = 0.281, η2p = 0.04) were not significantly different. Full demographic information can be found in Table 1 . Table 1 Participant demographics Variable N Mean ± SD Min – Max [Range] Age (yrs) Overall Female Male 32 15 17 25.19 ± 4.12 26.07 ± 4.17 24.41 ± 4.05 19.00–35.00 [16.00] 20.00–35.00 [15.00] 19.00–31.00 [12.00] Height (cm) Overall Female Male 32 15 17 173.78 ± 9.84 165.23 ± 5.73 181.34 ± 5.44 153.50–193.00 [39.50] 153.50–175.30 [21.80] 171.50–193.00 [21.50] Weight (kg) Overall Female Male 32 15 17 75.57 ± 13.22 64.47 ± 6.53 85.36 ± 9.16 52.40–103.00 [50.60] 52.40–76.30 [23.90] 66.80–103.00 [36.20] Body Fat Percentage Overall Female Male 32 15 17 23.28 ± 7.43 27.80 ± 6.19 19.29 ± 6.10 11.00–43.60 [32.60] 20.30–43.60 [23.30] 11.00–38.10 [27.10] VO2max (mL/kg/min) Overall Female Male 32 15 17 46.15 ± 7.43 42.14 ± 5.78 49.68 ± 7.03 31.20–62.60 [31.40] 32.50–50.60 [18.10] 31.20–62.60 [31.40] Projected 1-RM Squat (kg) Overall Female Male 32 15 17 108.21 ± 38.37 80.24 ± 15.19 133.32 ± 35.50 56.25–224.53 [168.28] 56.36–105.00 [48.64] 73.18 ± 225.00 [151.82] Projected 1-RM Bench (kg) Overall Female Male 32 15 17 77.14 ± 36.04 46.24 ± 11.94 104.71 ± 26.47 26.76–142.88 [116.12] 26.82–68.64 [41.82] 51.36–143.18 [91.82] Projected 1-RM Deadlift (kg) Overall Female Male 32 15 17 119.04 ± 42.27 87.67 ± 20.55 147.19 ± 36.62 58.97–221.81 [162.84] 59.09–124.55 [65.45] 95.91–221.27 [146.36] Values Reported as mean ± standard deviation. M = males, F = females; 1-RM = 1 repetition maximum. (Insert Table 1 ) 3.2 Acute Exercise Intensity Average heart rate (F(2, 62) = 395.57; p < 0.001, η2p = 0.93), core temperature (F(2, 62) = 132.16; p < 0.001, η2p = 0.81), skin temperature (F(2, 62) = 34.70; p < 0.001, η2p = 0.53), ventilatory rate (F(2, 62) = 160.68; p < 0.001, η2p = 0.84) were all significantly higher following AE and RE compared to CON. Additionally, Post-exercise BLC (F(2, 62) = 102.36; p < 0.001, η2p = 0.77) was all significantly higher following AE and RE compared to CON. Average heart rate ( p < 0.001) and ventilatory rate ( p < 0.001) were significantly higher during AE compared to RE. BLC ( p = 1.000), core temperature ( p = 1.000), and skin temperature ( p = 1.000) did not significantly differ between AE and RE. Duration of exercise session was significantly different between conditions (F(2,62) = 60.04; p < 0.001, η2p = 0.66). Post-hoc analysis suggests that RE duration was significantly longer than AE and CON ( ps < 0.001) and AE duration was significantly longer than CON ( p < 0.001). The gear time or time to transition from acute exercise, don firefighter gear and start the OTA was significantly different between conditions (CON: 6.03 ± 1.79, AE: 6.00 ± 1.51; RE: 8.81 ± 2.19; p = 0.001). Post-hoc analysis suggests the RE gear time was significantly longer than AE and CON ( p < 0.001). full report including mean and standard deviations of average as well as peak values for each of these variables can be found in Tables 2 and 3 . Table 2 Exercise prescription values Aerobic Session Low Interval High Interval RPE 3.86 ± 1.19 8.32 ± 1.11 Speed (km/h) 6.98 ± 1.42 19.78 ± 2.99 Resistance Session Squat Bench Deadlift Bent Row RPE 7.86 ± 1.03 7.93 ± 0.94 8.32 ± 0.81 7.42 ± 0.95 Reps 6.00 ± 0.00 5.96 ± 0.32 5.94 ± 0.24 6.00 ± 0.00 Load (kg) 191.15 ± 66.99 135.21 ± 63.59 206.72 ± 73.65 109.48 ± 44.70 RPE = Rating of Perceived Exertion (OMNI 0–10 scale) *Denote significantly different than control session; † Denotes significantly different than aerobic session. Statistical significance was set at p < 0.05. Table 3 Physiological response to acute exercise Variable Control Session Aerobic Exercise Resistance Exercise Peak HR (bpm) 105.53 ± 20.12 185.81 ± 10.43 172.22 ± 19.51 Avg HR (bpm) 74.07 ± 17.20 144.05 ± 8.43* 127.40 ± 19.62* † Peak VE (brpm) 24.88 ± 6.23 50.59 ± 7.40 37.78 ± 7.21 Avg VE (brpm) 15.54 ± 6.22 33.79 ± 4.71* 27.08 ± 4.08* † Peak ST (°C) 34.63 ± 0.76 36.61 ± 0.97 35.88 ± 2.11 Avg ST (°C) 33.16 ± 0.91 34.65 ± 1.25 34.71 ± 1.26 Peak CT (°C) 37.08 ± 0.27 38.42 ± 0.23 38.11 ± 0.48 Avg CT (°C) 36.91 ± 0.30 37.85 ± 0.23 37.79 ± 0.41 Post-BLC (mMol/L) 1.43 ± 0.50 8.31 ± 2.81 8.41 ± 3.35 Duration (minutes) 30.03 ± 0.18 26.97 ± 1.12 36.72 ± 6.09 Bpm = Beats/minute; Brpm = breaths/minute; °C = degrees Celsius; mMol = milliMol/Liter; *Denotes significantly different than control session; † Denotes significantly different than aerobic session. Statistical significance was set at p < 0.05. (Insert Tables 2 and 3 ) 3.3 Occupational Task Assessment Results Average time to complete was 1133.62 ± 261.62 sec after CON compared to 1197.83 ± 214.23 sec after AE and 1211.48 ± 301.62 sec after RE. ANOVA results suggest that there was not as significant difference between pre-OTA conditions (F(2,54) = 1.88; p = 0.162; η2p = 0.07). Based on our equivalence test, we rejected the presence of effects in time to complete OTA between conditions more extreme than η2p = 0.11, or 3 minutes ( p = 0.014). Visual representation of the average time to complete the OTA between conditions can be found in Fig. 1 . (Insert Fig. 1 ) Heart rate (F(2, 62) = 47.04; p < 0.001, η2p = 0.60), core temperature (F(2, 62) = 195.00; p < 0.001; η2p = 0.86), skin temperature (F(2, 62) = 38.69; p < 0.001; η2p = 0.56), and ventilatory rate (F(2, 62) = 7.98; p < 0.001; η2p = 0.21) were all significantly different between conditions during OTA. BLC immediate-post OTA was not significantly different (F(1, 62) = 2.794; p = 0.072; η2p = 0.09). Post hoc analysis revealed heart rate during the OTA was significantly higher following AE and RE compared to CON and significantly lower after RE compared to AE ( ps < 0.002). Core temperature was significantly higher during OTA following RE and AE compared to CON, and RE was significantly lower than AE ( ps < 0.002). Skin temperature was significantly higher during OTA following AE and RE compared to CON, and RE was also significantly lower than AE ( ps < 0.001). Ventilatory rate was significantly higher during OTA following AE and RE compared to CON ( ps < 0.004), but AE was not different from RE ( p = 1.000). When comparing peak physiological response experienced, max core temperature was significantly different by condition (F(2, 62) = 102.12; p < 0.001, η2p = 0.77). Post-hoc analysis indicated max core temperature was significantly higher following AE compared to both CON ( p < 0.001) and RE ( p = 0.002) and RE was significantly higher than CON ( p < 0.001). Average RPE was significantly different by condition (F(2, 62) = 26.83; p < 0.001; η2p = 0.46). Post hoc analysis revealed RPE during OTA was significantly higher following AE and RE compared to CON ( ps < 0.001), but not significantly different between AE and RE ( p = 1.000). Additionally, gear time (time between acute exercise and OTA) was significantly longer (F(2, 56) = 31.55; p < 0.001, η2p = 0.53). Post-hoc analysis showed gear time was significantly longer following RE compared to AE and CON ( p < 0.001), but AE was not significantly different from CON ( p = 1.000). AUC (cumulative heat stress experienced during OTA) was significantly different by condition (F(2, 60) = 15.66; p < 0.001, η2p = 0.34). Post-hoc analysis revealed AUC was significantly higher following AE and RE compared to CON ( ps < 0.010), but not different between AE and RE ( p = 0.092). Mean and standard deviations for average in these physiological variables and perception of exertion can be found in Tables 4 . Pre- to post-OTA blood lactate concentrations are visually represented in Fig. 2 . Graphs highlighting the rate of increase in these physiological variables can be found in Figs. 3 . Table 4 Physiological response and perceived exertion during OTA Variable Control Aerobic Exercise Resistance Exercise Average Heart Rate (bpm) 148.49 ± 16.22 † 166.28 ± 11.47* 159.91 ± 12.99* † Average Ventilation Rate (brpm) 37.19 ± 4.78 † 40.24 ± 6.58* 39.69 ± 5.49* Average Skin Temperature (°C) 36.33 ± 0.54 † 37.48 ± 0.58* 36.87 ± 0.86* † Average Core Temperature (°C) 37.56 ± 0.35 † 38.68 ± 0.26* 38.44 ± 0.46* † Pre-Chamber BLC (mMol/L) 1.54 ± 0.56 7.13 ± 2.50 6.15 ± 2.65 Post Chamber BLC (mMol/L) 7.85 ± 3.94 7.10 ± 2.62 8.58 ± 3.71 Average RPE 12.72 ± 1.79 14.27 ± 1.56* 14.69 ± 1.62* Bpm = Beats/minute; Brpm = breaths/minute; °C = degrees Celsius; RPE = Rating of Perceived Exertion (Borg 6–20) *Denotes significantly different than control session; † Denotes significantly different than aerobic session. Statistical significance was set at p < 0.05. (Insert Figs. 2 and 3 + Table 4 ) 3.4 Recovery Responses During recovery, there were not statistically significant differences in average heart rate (F(2, 62) = 1.17; p = 0.318; η2p = 0.04), core temperature (F(2, 62) = 1.85; p = 0.165; η2p = 0.06), skin temperature (F(2, 62) = 0.10; p = 0.905; η2p < 0.01), ventilatory rate (F(2, 62) = 0.49; p = 0.618; η2p = 0.02), or change in BLC (F(2, 62) = 1.84; p = 0.168; η2p = 0.06). There was a significant difference in AUC between conditions (F(2, 62) = 70.94; p 0.001), but AE and RE were not significantly different ( p = 0.630). A visual representation of the rate of recovery for these variables are included in Fig. 4 . (Insert Fig. 4 ) 4 DISCUSSION NFPA recommends firefighters exercise on-shift [ 51 ]. Previous research suggests firefighters frequently have on-site access to barbells and treadmills allowing them to complete both aerobic and resistance exercise on shift [ 28 ]. However, firefighters have expressed concerns that exercising on-shift may decrease their ability to respond to emergency calls, making it important to understand the impact acute on-shift exercise has on firefighter occupational performance. Therefore, this study aimed to determine if resistance or aerobic training impacts occupational performance and physiological strain. Contrary to our primary hypothesis, we did not find evidence that exercise modality impacted occupational performance, despite finding evidence of elevated markers of physiological and perceptual strain (elevated skin temperature, core temperature, heart rate, and RPE) in both AE and RE conditions compared to CON. These findings differed from previous research investigating the effect of acute exercise on occupational performance [ 31 , 32 ]. Methodological differences likely contributed to the differences in findings. The aim of both previous investigations involved an acute exercise prescription of high-intensity circuit-style resistance training [ 31 , 32 ]. This has good application, as many firefighters currently engage in this form of exercise training. Our study aimed to add to these findings through the comparison of conventional resistance exercises and high-intensity interval training (HIIT), to help elucidate how the two exercise stressors may impact occupational performance differently. The divergence in findings may also relate to the circuit-style fashion, which can replicate more similar demands (repeated lifting and moving tasks with minimal rest) resulting in fatigue of the same musculature and depletion of the same substrates utilized during occupational tasks to a greater degree than resistance or aerobic exercise, therefore leading to larger interference with occupational performance. Taken together, these finding provide a more comprehensive understanding of how different training methods may have unique impacts on occupational performance. Core temperature, heart rate, and skin temperature were all elevated in the acute exercise conditions when compared to CON and elevated the most following AE even though numerically higher RPE and time to complete occupational tasks was ~ 30 sec slower following RE. An elevated core temperature following an acute bout of aerobic exercise could potentially limit a firefighter’s ability to continue work during extended operations (longer than the average 20 minutes experienced in this study), possibly putting firefighters at an increased risk for fatigue and exertional heat injury [ 52 ]. This is already a primary concern of fire services [ 53 ], with almost 75% of firefighters experiencing heat injury symptoms in a calendar year [ 54 ]. These elevated physiological responses warrant future investigations involving longer occupational task assessments to further elucidate this risk. Participants in our study did not use a SCBA during our investigation, because firefighters would not utilize a SCBA during the operations we intended to replicate, However, ventilatory rates were investigated because of the relationship between breathing rate, oxygen consumption, and the depletion of the air experienced when a firefighter is using a self-contained breathing apparatus (SCBA). Previous research has shown that acute exercise 10 minutes before an occupational task assessment, but not 60 minutes prior, increased air depletion [ 32 ]. Our results indicate ventilatory rates were significantly higher during acute exercise (AE and RE) compared to CON. This may suggest prior acute exercise may influence SCBA depletion rate. However, this is speculative as we did not assess the SCBA depletion in this study. Unlike the previously mentioned variables, BLC was not significantly different between conditions, possibly due to the use of a high-intensity interval-based aerobic workout. A long, slow continuous aerobic workout may have resulted in lower lactate levels going into the OTA, resulting in lower post-OTA BLC. An interesting observation was that participants, on average, experienced almost no change (0.03 mMol/L decrease) in BLC following AE; while there was a 2.4 mMol/L increase following RE. This could be a result of increased reliance on rapid glycolysis aerobic metabolism and subsequently higher lactate accumulation during the OTA following RE, compared to AE. This difference was not statistically significant, although there was a moderate effect (η2p = 0.09). This warrants future investigations into lactate response and its influence on occupational demands, specifically in higher intensity or even longer duration tasks where lactate levels may limit performance. When considering the physiological responses experienced it is worth considering the average time to complete the tasks and the type of tasks completed in this study compared to previous work. In previous investigations, the times to complete occupational tasks were ~ 7 minutes or less [ 31 , 32 ], while we aimed to understand acute exercise’s impact on extended occupational tasks (~ 20 minutes in duration). Taken with the physiological variables measured across our study and previous work we can reasonably consider that acute exercise may decrease performance of short, high-intensity occupational demands through increased fatigue from acidosis; while increasing heat injury risk during longer, moderately high-intensity tasks due to increases in core temperature. This is supported by the lower levels of blood lactate concentrations following our occupational tasks compared to previous studies [ 31 , 32 ] and elevated core temperatures observed in the current investigation. While the current and previous investigations provide an understanding of acute exercise’s impact on both short and moderate duration occupational tasks [ 31 , 32 ], firefighting scenarios can extend to longer durations. When considering a firefighter’s SCBA lasts on average 30–60 min [ 55 ] and it worth investigating occupational scenarios of this duration in future work. In addition to the increased physiological strain experienced during the OTA, perceived exertion was elevated following both RE and AE when compared to CON. This could likely be a consequence of the elevated core temperature and skin temperature increasing thermal stress, resulting in the OTA feeling more demanding even though participants were able to complete the tasks at the same rate. Acute exercise bouts did not impair the rate at which participants recovered following occupational task performance, contrary to our secondary hypothesis. We hypothesized aerobic exercise would have a slower rate of recovery following the OTA due to the added volume of exertion from acute exercise. Yet, our findings indicate heart rate, core temperature, skin temperature, ventilatory rate, and blood lactate concentrations were not significantly different on average or at the end of the 40-minute recovery. However, AUC between conditions was elevated during recovery from AE and RE. This suggests the individuals’ core temperature spent a larger portion of the recovery at an elevated level. There may have been elevated fatigue or thermal stress experienced that was not accounted for in the current investigation, even though participants returned to similar resting values. This could impact subsequent occupational readiness for future calls during their shift. An important limitation of this study to note is the choice to use members of the community rather than current firefighters. We acknowledge that firefighters have unique experiences working in the heat [ 56 ], and previous research has suggested that long-term, career firefighters do experience specific heat adaptations that may differ from the experiences of the population sampled in the current investigation [ 57 ]. Additionally, previous literature suggests that firefighters are on average older and have poorer cardiovascular outcomes [ 58 ] than our relatively young and healthy sample which may impact the responses seen. However, this was an intentional decision as the local fire departments in our area are younger [ 59 ] and more physically active [ 28 ] than the national average, similar to the sample presented in our investigation. Therefore, when considering this and the limited number of local firefighters and more specifically female firefighters the use of local community ensured an adequate and diverse sample population. This population also aids in understanding the responses experienced by new firefighters that have not yet experienced these adaptations. Additionally, the movements chosen for the OTA in this study were based on recommendations of the local fire department, which were limited based on the confines of our environmental chamber and do not represent all firefighting task demands. We also did not measure thermal sensation, which would have provided supplemental information to help understand potential behavioral thermoregulatory measures (i.e., slowing pace down or stopping between tasks) that may have been impacted by an acute exercise bout. Lastly, the gear time was ~ 2–3 minutes longer following the resistance training session compared to aerobic and resting control partly due to the location of our weight room being further from our environmental chamber than our aerobic and control testing area. This gear time was not standardized as we wanted to replicate immediate post-exercise conditions with no rest. While this difference could have had a small impact on OTA responses; had we standardized the rest period, the participants would have had 2–3 minutes of passive rest prior to entering the chamber after the aerobic and resting control conditions, which would have likely had a larger impact on OTA responses. The current study sought to determine immediate decrements from acute exercise on occupational performance. However, if the call comes in hours after on-shift exercise fatigue, delayed onset muscle soreness, and other factors may differentially influence occupational readiness. One study aimed to address the difference between a 10-minute and 60-minute post-exercise occupational task assessment. The findings suggested that while there were impairments at 10-minutes, they were statistically recovered by 60-minutes post-exercise [ 32 ]. The potential for an emergency call to arrive at any time during their work shift warrants further investigation into the time course of the impact of acute exercise on occupational tasks. In addition to the considerations of on-shift exercise, off-shift exercise presents its own considerations in future research, specifically for factors related to substrate availability and delayed on-set muscle soreness. Lastly, we chose conventional strength training and high-intensity interval training based on the common equipment resources accessible [ 28 ] and preferred methods of aerobic training of firefighters as well as the demand for both strength and aerobic capacity in firefighters. However, there are a multitude of different exercise prescription choices that could influence the acute response to exercise (i.e., sets, reps, intensity, rest intervals, and movements chosen) that should be investigated in the future to fully understand prescription recommendations to optimize improvements in occupationally relevant fitness while minimizing decrements in occupational readiness in fire services. 5 CONCLUSIONS The data presented suggest a firefighter may be able to exercise while on-shift and respond to a call without meaningful decrements in performance. However, these potential increases in physiological strain provide precautionary data that individual’s may be at an increased risk of overexertion or heat-related injury while completing occupational tasks if they exercised immediately beforehand. This risk may be even higher after aerobic exercise even though rating of perceived exertion, post-OTA blood lactate concentrations, and time to complete were numerically higher after resistance exercise. Fire departments and fitness professionals working with fire services can utilize these findings to guide training programs. With the knowledge that aerobic fitness and muscular strength are required for this population to meet the demands of their occupations, it is important we understand how to address fitness most effectively and efficiently without interfering with their occupational readiness. Even though there was a larger numeric decrease in time to complete occupational tasks when resistance exercise was performed prior (2.5% longer than when aerobic exercise was performed), the risk for heat related illness is a more important consideration for fire services. Therefore, it may be beneficial for fire service strength and conditioning professionals to prescribe aerobic exercise off-shift and focus on resistance exercise on-shift to minimize heat illness while still working toward improvements in fitness through the implementation of on-shift exercise. However, limitations related to adherence to unsupervised exercise may make this difficult. If aerobic exercise is performed on-shift, firefighters should be aware of the potential increased risks, and take precautions including the utilization of cooling methods to mitigate this increase during exercise. Declarations We have no funding sources to declare for this study. Consent to participate Informed consent was obtained from all individual participants included in the study. Ethical Approval The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board (or Ethics Committee) of Auburn University (protocol code #22–149 MR 2205, 05/05/2022). Conflict of Interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Funding Sources The authors declare no funding was received for this project. Author Contribution Conceptualization, PJA, JMS, CBM, MWM, WMM; Data curation, PJA and NCB; Formal analysis, PA.; Investigation PJA, NCB, PLJ, AMR., LFR; Methodology, PJA, JMS, CBM, MWM, WMM; Project administration, PJA, NCB, PLJ, AMR, LFR; Supervision, JMS; Visualization, PJA; Writing—original draft, PJA, NCB; Writing—review and editing, all authors. Acknowledgement We would like to thank our research volunteers for assisting with data collection, and the participants for their time and efforts. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4547891","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":325513603,"identity":"bccae7cc-23bb-423a-b838-f07e1ee01c18","order_by":0,"name":"Philip Agostinelli","email":"","orcid":"","institution":"Auburn University","correspondingAuthor":false,"prefix":"","firstName":"Philip","middleName":"","lastName":"Agostinelli","suffix":""},{"id":325513604,"identity":"3da04991-aab4-441d-b6f3-20da0652e6bf","order_by":1,"name":"Nicholas C. Bordonie","email":"","orcid":"","institution":"Auburn University","correspondingAuthor":false,"prefix":"","firstName":"Nicholas","middleName":"C.","lastName":"Bordonie","suffix":""},{"id":325513606,"identity":"61ff5a54-5360-4c28-97d0-850016ef7400","order_by":2,"name":"Ann M. Robbins","email":"","orcid":"","institution":"Auburn University","correspondingAuthor":false,"prefix":"","firstName":"Ann","middleName":"M.","lastName":"Robbins","suffix":""},{"id":325513608,"identity":"85afac39-2d2b-4dd5-be1f-992f0d8d88d7","order_by":3,"name":"Parker L. Jones","email":"","orcid":"","institution":"Auburn University","correspondingAuthor":false,"prefix":"","firstName":"Parker","middleName":"L.","lastName":"Jones","suffix":""},{"id":325513610,"identity":"9cf6587c-4cc1-4dc2-8677-3e5386480c6b","order_by":4,"name":"Lee F. Reagan","email":"","orcid":"","institution":"Auburn University","correspondingAuthor":false,"prefix":"","firstName":"Lee","middleName":"F.","lastName":"Reagan","suffix":""},{"id":325513611,"identity":"ad6268d7-74ec-4dce-8523-c19960288085","order_by":5,"name":"C. Brooks Mobley","email":"","orcid":"","institution":"Auburn University","correspondingAuthor":false,"prefix":"","firstName":"C.","middleName":"Brooks","lastName":"Mobley","suffix":""},{"id":325513612,"identity":"5c59fd3e-5c9c-4971-badb-eeee293e8c5b","order_by":6,"name":"Matthew W. Miller","email":"","orcid":"","institution":"Auburn University","correspondingAuthor":false,"prefix":"","firstName":"Matthew","middleName":"W.","lastName":"Miller","suffix":""},{"id":325513613,"identity":"4b4dc28b-cf91-48c9-98ca-c37c3e9f65c2","order_by":7,"name":"William M. Murrah","email":"","orcid":"","institution":"Auburn University","correspondingAuthor":false,"prefix":"","firstName":"William","middleName":"M.","lastName":"Murrah","suffix":""},{"id":325513614,"identity":"3003052e-97f7-4b7a-85ea-78294f97894a","order_by":8,"name":"JoEllen M. Sefton","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzUlEQVRIiWNgGAWjYBACxgYGhgMJBjZyDAw8UKEDhLUwPvhQkGZMvBYgYDac8eFwYgPRWpinHX8mzWOQlt4/I/eYdOUOBjm+GwkEHDY7xwyoxSZ3xo28NMmzZxiMJYnQwgayJbfhRo6ZZGMbQ+IGwlrSQQ47nC4P1VJPhJYEY8MZBocTDKBagAzCDjN88MEgzXDjmXfJlo1tEoYzzzzAr8VwdvqDAwl/bOTljucevNnYZiPPd5yALYYNqHwJ/MpBQJ6wklEwCkbBKBjxAADLAUjaIHP54AAAAABJRU5ErkJggg==","orcid":"","institution":"Auburn University","correspondingAuthor":true,"prefix":"","firstName":"JoEllen","middleName":"M.","lastName":"Sefton","suffix":""}],"badges":[],"createdAt":"2024-06-07 19:45:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4547891/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4547891/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-024-81015-8","type":"published","date":"2024-11-30T15:58:34+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":60404986,"identity":"abef02f3-7a56-4e97-8ec4-20909098d416","added_by":"auto","created_at":"2024-07-16 11:51:36","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":29414,"visible":true,"origin":"","legend":"\u003cp\u003eOccupational Task Assessment (OTA); Differences in time to complete across each pre-OTA condition. CON: resting control; AE: aerobic exercise; RE: resistance exercise. No significant differences present (ps \u0026gt; 0.05).\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-4547891/v1/d5bd3ca7486d35156dba68fe.png"},{"id":60404979,"identity":"08a3cb7d-2d0a-4b6e-b28d-68d803bbe8e2","added_by":"auto","created_at":"2024-07-16 11:51:33","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":30608,"visible":true,"origin":"","legend":"\u003cp\u003eBlood lactate concentrations immediately before (Pre) and immediate post (IMP) Occupational Task Assessment (OTA) based on pre-OTA condition. CON: resting control; AE: aerobic exercise; RE: resistance exercise. No significant differences present (ps \u0026gt; 0.05). Data is presented as mean and individual values.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-4547891/v1/93f54f3734943700c653517a.png"},{"id":60404982,"identity":"711b21a0-eeeb-4a73-a3be-2e6ba53b18c7","added_by":"auto","created_at":"2024-07-16 11:51:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":222681,"visible":true,"origin":"","legend":"\u003cp\u003ePhysiological Strain during the Occupational Task Assessment (OTA) based on pre-OTA conditions. CON: resting control; AE: aerobic exercise; RE: resistance exercise. \u003csup\u003e\u003cstrong\u003ea\u003c/strong\u003e\u003c/sup\u003eDenotes significant difference from aerobic; \u003csup\u003e\u003cstrong\u003eb\u003c/strong\u003e\u003c/sup\u003eDenotes significant difference from resistance;\u003csup\u003e \u003c/sup\u003e\u003csup\u003e\u003cstrong\u003ec\u003c/strong\u003e\u003c/sup\u003eDenotes significant difference from control; (p \u0026lt; 0.05); Values represented are 4-minute mean and standard deviation.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-4547891/v1/0a291e2c50aa738f29a15674.png"},{"id":60404988,"identity":"de75ffa5-ab15-4f3d-8629-a1ca7bdecfcb","added_by":"auto","created_at":"2024-07-16 11:51:36","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":263331,"visible":true,"origin":"","legend":"\u003cp\u003eRate of recovery of physiological variables following Occupational Task Assessment (OTA) based pre-OTA condition. CON: resting control; AE: aerobic exercise; RE: resistance exercise. No significant differences present (ps \u0026gt; 0.05). Values represented are mean and standard deviation.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-4547891/v1/2d85040a8260f93c36ebd698.png"},{"id":70389543,"identity":"d2e01b47-84d3-4e38-83d2-8b9695b1df92","added_by":"auto","created_at":"2024-12-02 17:28:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1274349,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4547891/v1/b6d58d76-dac4-470b-b906-1238c116a772.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Impact of acute exercise on performance and physiological stress during simulated firefighter occupational tasks","fulltext":[{"header":"1 INTRODUCTION","content":"\u003cp\u003eFirefighters are exposed to a broad spectrum of environments typically divided into two types: fireground (vehicle fires, wildfires, structural fires) and non-fireground (medical emergencies, vehicle accidents, natural disasters). Both can present a risk for heat stress ranging from hot summer temperatures upwards of 32\u0026deg;C, with wildland fire suppression reaching 78\u0026deg;C [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] and structural fires reaching extreme temperatures of 300\u0026deg;C [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Personal protective equipment (PPE) worn to protect firefighters from extreme heat weighs approximately 17\u0026ndash;25 kg [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. This added weight and restricted movement can exacerbate the stress imposed on the firefighters and limit occupational performance [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. These high levels of physical and environmental stress imposed on firefighters reinforce the need for fitness training opportunities and physical fitness standards. A study looking at the adaptations to fire academy training saw significant improvements in fitness during academy training that were subsequently lost when reassessed following firefighters\u0026rsquo; probationary period (8 months later). This included declines in body composition, aerobic capacity, muscular strength, and muscular endurance, suggesting overall health and fitness declined once firefighters left the academy [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. A National Fire Prevention Association (NFPA) report notes that 70% of firefighters do not meet recommended health and fitness guidelines [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. This raises concern as research suggests poor fitness and lack of a well-designed training program decrease occupational performance and increase firefighters\u0026rsquo; risk for overexertion injuries [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] and increase cardiovascular disease/event risk [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eResearch on exercise interventions in firefighters has revealed promising improvements in occupationally relevant fitness parameters, including general health outcomes [\u003cspan additionalcitationids=\"CR15 CR16\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] and occupational performance [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. However, only 27% of fire departments across the United States provide health and fitness programs [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Research has shown that firefighters who participated in on-shift (within the station) physical activity accumulated a higher level of total physical activity on a weekly basis and had better cardiovascular health indicators over those that do not [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The importance of maintaining physical fitness despite the hectic work schedule makes it crucial that firefighters are provided time to exercise while on shift. However, it is important to consider the cumulative exertional stress this could impose.\u003c/p\u003e \u003cp\u003eCurrent literature indicates physiological measures (i.e., heart rate, skin temperature, ventilation, and core temperature) are intensified when performing simulated firefighting tasks [\u003cspan additionalcitationids=\"CR20 CR21 CR22 CR23\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Core temperature, heart rate, lactate concentrations, and workload are all increased in heated environments [\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Firefighters have expressed uncertainty about adding the physiological stress of on-shift exercise to the stress of their daily job tasks [\u003cspan additionalcitationids=\"CR29\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], concerned the added stress response may lead to decrements in occupational performance. Two studies have investigated the effects of exercise training-induced fatigue on simulated firefighting tasks and the physiological stress experienced after a bout of acute exercise. They reported a 9.6% [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] and 45% [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] increase in time to complete 10-minutes after acute exercise and a 9.8% increase in time to complete 60 minutes after exercise [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. These studies suggests that a single on-shift exercise session may transiently impair the ability to meet occupational requirements. While one of these studies used circuit style training and the other involved high-intensity resistance training, no study to our knowledge has directly compared the acute impact of resistance training and aerobic endurance training on the physiological readiness of firefighters.\u003c/p\u003e \u003cp\u003eTherefore, the purpose of this study was to investigate the impact of resistance and aerobic endurance exercise on physiological outcomes and performance related to firefighter occupational performance. We hypothesized that aerobic exercise would have a greater impact on occupational performance compared to resistance training, by increasing time to complete and markers of physiological strain and fatigue (heart rate, skin temperature, ventilation, core temperature, and blood lactate concentrations). A secondary aim was to determine if the acute exercise bouts impair the rate at which the physiological variables recover following occupational task performance. We hypothesized that aerobic exercise would result in a slower rate of recovery following occupational task recovery compared to resistance training.\u003c/p\u003e"},{"header":"2 METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Study Design\u003c/h2\u003e \u003cp\u003eThis study utilized a repeated measures quasi-randomized control trial. Participants were local members of the community rather than firefighters. This decision was made in order to obtain an adequate sample size for the statistical analysis. Each participant completed a series of baseline assessments for cognitive, physiological, aerobic, and anaerobic performance outcome measures as a part of the larger study that was approved by the Institutional Review Board at Auburn University (IRB protocol code #22\u0026ndash;479 AR 2211, 05/05/2022). These baseline assessments have been outlined below as we will utilize values to quantify the fitness level of the population. Participants then completed three exercise sessions in quasi-randomized order: 1) resistance exercise (RE); 2) aerobic high-intensity interval training (AE); or 3) rested control (CON). Each exercise session was directly followed by an occupational task assessment (OTA). A seven-day wash-out period was included between trials to reduce the risk of residual fatigue impacting subsequent trial performance. Participants completed the CON condition second to reduce the number of potential unique trial order group comparisons. Block randomization of trial order of exercise type was generated in Microsoft\u0026reg; Excel (Microsoft Corporations, Redmond, WA USA) by a co-investigator and reported allocations to the lead author (PA). Independent variables included Pre-OTA condition (AE, RE, CON). The primary dependent variable was OTA time to complete, with secondary dependent variables including core temperature, blood lactate concentrations (BLC), skin temperature, heart rate, and ventilatory rate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Participants\u003c/h2\u003e \u003cp\u003eForty-one individuals were enrolled in the study. Thirty-two (15 males, 17 females) participants completed all study requirements (25.19\u0026thinsp;\u0026plusmn;\u0026thinsp;4.12 yrs., 173.78\u0026thinsp;\u0026plusmn;\u0026thinsp;9.84 cm, 75.57\u0026thinsp;\u0026plusmn;\u0026thinsp;13.22 kg, 23.28\u0026thinsp;\u0026plusmn;\u0026thinsp;7.43% body fat). All participants were individuals from the local community, none of which were current firefighters. Additionally, all participants met the following inclusion criteria: (i) 19\u0026ndash;45 years of age, (ii) free of musculoskeletal injury, (iii) available to complete the full 5-week study timeline, (iv) comfortable carrying out exercise tasks while in a heat chamber, (v) agreed to adhere to study requirements, and (vi) passed a health screening. Participants were excluded if they: (i) had a known medical condition, physical or psychological condition, preventing participation in exercise, (ii) had a current musculoskeletal injury or were rehabilitating from a recent one, (iii) had been diagnosed with asthma (defined as experienced symptoms, or prescribed any form of treatment within the past 4 years), (iv) had a history of heart condition or high blood pressure, (v) experienced pain in chest at rest, during activities of daily living, or when performing physical activity or exercise, (vi) had been prescribed medically supervised physical activity only by a primary care physician, or (vii) had recently experienced a heat related illness or injury (i.e., heat exhaustion, heat stroke, etc.). Informed consent was obtained by lead author (PA) prior to enrollment in the study. No interested participants were excluded. Out of the forty-one enrolled, five participants withdrew due to scheduling conflicts, three withdrew due to difficulty, one was withdrawn for not adhering to study protocols.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Procedures\u003c/h2\u003e \u003cp\u003eAll study procedures occurred in the School of Kinesiology buildings starting in January of 2023 and ending in August of 2023 when appropriate power was obtained. Each participant completed a baseline fitness assessment (Day A and B) prior to completing the acute exercise trials (Trials 1\u0026ndash;3). Participants were asked to refrain from caffeine and recent exercise for 24 hours leading up to Day A and Day B. Adequate hydration (USG\u0026thinsp;\u0026lt;\u0026thinsp;1.02) of each participant was assessed before testing on Day A and Day B. The urine sample was analyzed with a refractometer (V-Resourcing, Hunan, China) for hydration status. If the participant was dehydrated (USG\u0026thinsp;=\u0026thinsp;\u0026gt;\u0026thinsp;1.02), they were provided 16 oz of water to drink and provided a new urine sample. All participants were adequately hydrated before they began baseline testing. Participants were encouraged to schedule visits at the same time of day and maintain a consistent diet during the duration of the study, however, this was not controlled.\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.3.1 Day A (Body Composition and Aerobic Fitness)\u003c/h2\u003e \u003cp\u003eBody composition (fat, muscle, and bone mineral density) was measured with a full-body dual-energy X-ray absorptiometry (DXA) scan (Lunar Prodigy; GE Healthcare, Chicago, IL, USA). Participant\u0026rsquo;s height and weight were obtained utilizing a digital scale and stadiometer (SECA, Hamburg, Germany).\u003c/p\u003e \u003cp\u003ePeak oxygen consumption (VO\u003csub\u003e2\u003c/sub\u003epeak) was assessed as a measure of cardiorespiratory fitness level utilizing a modified Bruce protocol [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] for treadmill (Woodway, Waukesha, WI, USA) graded exercise testing. Participants were asked to give their best effort and continue until they could go no longer. The test was terminated once participants reached volitional fatigue. VO\u003csub\u003e2\u003c/sub\u003epeak was determined as the maximal oxygen consumption achieved during the test. Respiratory exchange ratio (RER\u0026thinsp;\u0026gt;\u0026thinsp;1.15), HRmax (within 10 bpm of age-predicted max), BLC (\u0026gt;\u0026thinsp;8.0 mM), and volitional fatigue, were utilized to verify a valid maximal effort was given by the participant. Additionally, lactate threshold was estimated as part of the larger study. The participant\u0026rsquo;s fingertips were disinfected using an alcohol wipe and dried with a gauze pad. Once dried, a fingerstick was administered using a BD Microtainer \u0026reg; auto-lancet (BD, Franklin Lakes, NJ USA) to draw a drop of blood from the participant\u0026rsquo;s fingertip. The first drop was wiped by the gauze pad and the second drop of blood was placed on the lactate test strip and inserted into the Nova Biomedical Lactate Plus Meter (Nova Biomedical, Waltham, MA USA) for measurement. The Lactate Plus Meter was calibrated bi-weekly during testing with low and high control solutions and the accuracy was confirmed to be within acceptable limits (i.e., low control solution: 1.0\u0026ndash;1.6 mmol/L; high control solution: 4.0\u0026ndash;5.4 mmol/L).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.3.2 Day B (Muscular Strength, Power, and Familiarization)\u003c/h2\u003e \u003cp\u003eParticipants completed a counter-movement vertical jump on a Leonardo Mechanograph force platform (Novotec Medical GmbH, Pforzheim, Germany) as an assessment of lower body muscular power. The participant stepped onto the platform and was instructed by the research team to jump as high as possible. This task was completed three times with a one-minute rest between attempts.\u003c/p\u003e \u003cp\u003eThree repetition maximum testing (3RM) performance was used to determine training load during the acute resistance training session, as well as an indicator of muscular strength. The squat, bench press, and hex-bar deadlift movements were used to assess upper and lower body strength. During each attempt, participants were provided spotters. For the squat, the participants were asked to place the barbell and attached weights on the top of the shoulders behind the head and completed a full squat. If the participant\u0026rsquo;s back angle began to change on the repetition, it was not counted. For bench press, they started by laying on their back on a lifting bench setting five points of contact (head, shoulders, buttocks, and both feet flat on the floor). To complete the lift, the participant touched the bar to the chest (with a slight pause at the chest) and raised back up to the starting position. For the hex-bar deadlift, the participants lifted the weight bar from the ground, with both knees and hips bent while maintaining a constant back angle throughout. If the weight was hiked or slid up the thighs or their back angle changed, the repetition was not counted. The hex-bar deadlift was utilized to reduce technical errors and potential injury risk in inexperienced lifters [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The participants were monitored by a certified strength and conditioning specialist (author - P.A.) to ensure they performed each exercise completely and with proper form. Participants started the 3RM protocol by completing the lift with a series of warm-up lifts (45-lb bar for 8\u0026ndash;10 reps, 50% of projected 1-RM for 6\u0026ndash;8 reps, 75% for 3\u0026ndash;5 reps, and 85% for 1\u0026ndash;3 reps). Their first attempt was at 95% of self-reported 3RM. Each set included a minimum of two minutes of rest and a maximum of five minutes of rest. The maximum weight completed for three reps while maintaining good form was utilized to project 1RM based on the National Strength and Conditioning Association\u0026rsquo;s (NSCA) guidelines [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. If participants only achieved one or two reps at attempted weight, that value was taken and utilized to project 1RM. During Day B, participants were also familiarized with the Occupational Task Assessment (OTA). They were instructed on how to don the standard firefighter PPE, including turn-out gear, gloves, boots, and a helmet. After which, they entered the chamber that was set at 35\u0026deg;C (95\u0026deg;F) with 50% relative humidity and practiced one round of the OTA to reduce any learning effect associated with the OTA.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Experimental Trials\u003c/h2\u003e \u003cp\u003eAfter the fitness assessments (Day A and B), the participants completed the acute exercise trials (Trials 1\u0026ndash;3). Participants were asked to refrain from caffeine and exercise during the 24 hours leading up to each of the three trials. Participant hydration was tested before each trial. If the participant was dehydrated, they were provided with water to drink and provided a new urine sample for analysis. Each of the acute exercise sessions were lead and monitored by a certified strength and conditioning professional (P.J.A) and at least one other researcher.\u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.5.1 Acute Exercise and Control Trials\u003c/h2\u003e \u003cp\u003eThe full-body resistance exercise session was programmed utilizing NSCA guidelines for strength training [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Prior to starting the RE session, participants completed a structured warm-up. The warm-up protocol followed the NSCA\u0026rsquo;s recommended structure of a general and specific warm-up involving a moderate-paced walk on a treadmill [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] and dynamic movements that mimicked and prepared the participant for the movement patterns of the acute resistance exercises, including bodyweight squats, hip rotations, scapular protraction and retraction [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. After the warm-up, participants completed four exercises emphasizing each major movement in the following order:1) back squat, 2) barbell bench press, 3) hex-bar deadlift, and 4) barbell bent-over rows. Participants completed three sets of six repetitions of each exercise at ~\u0026thinsp;80% of their projected 1-RM from baseline testing with two minutes of rest between sets. If a participant was unable to complete a set at the prescribed weight, the weight was lowered until the set was finished and remained at that weight for subsequent sets. BLC measurements were taken pre- and post-exercise. Total exercise time varied between resistance session, due to variability in the number of warm-up sets needed based on working weight.\u003c/p\u003e \u003cp\u003eThe aerobic bout involved high-intensity interval training (HIIT). This exercise session was programmed utilizing NSCA guidelines for aerobic endurance training and a 2018 investigation of a cycling HIIT protocol [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Prior to starting the AE session, participants completed a structured warm-up. The warm-up protocol followed the NSCA\u0026rsquo;s recommended structure of a general warm-up, involving a moderate-paced walk (4.8 kph) on a treadmill [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Each participant completed five rounds of four minutes of low-intensity exercise at approximately 50% of heart rate reserve (HRR) and 30 seconds of high intensity at approximately 90% of HRR on a treadmill. The HRR values were calculated with the Karvonen method [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] utilizing resting and max heart rate values from the baseline assessments. BLC measurements were taken pre- and post-exercise. The aerobic exercise session was programmed to take approximately 27 minutes.\u003c/p\u003e \u003cp\u003eA control session was completed to assess any effect of exercise in general, regardless of modality. This control session involved having participants sit in our laboratory in a quiet, controlled environment where they could work on their laptops, scroll on their phones, browse the internet, or read a book. However, participants were told to avoid any stressful or overstimulating work, and activities during the 30-minute time frame were recorded. The activity choices were decided in tandem with what the local Fire Department described as activities that firefighters typically partake in during their on-duty downtime. BLC measurements were taken pre- and post-control session.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.5.2 Transition Period\u003c/h2\u003e \u003cp\u003eParticipants then donned standard firefighting turnout gear and PPE as they would during a live emergency call. BLC was once again assessed prior to entering the environmental chamber where participants completed the simulated occupational task assessment.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e2.5.3 Occupational Task Assessment (OTA)\u003c/h2\u003e \u003cp\u003eThe environmental chamber conditions were set to 35\u0026deg;C (95\u0026deg;F) with 50% relative humidity to mimic temperatures experienced during highway extractions on a hot summer day, other outdoor emergencies, and salvage [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. This temperature was chosen, rather than hotter temperatures, to replicate non-fireground scenarios known to constitute\u0026thinsp;~\u0026thinsp;80% of firefighters' emergency calls in the southeastern United States [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Inside the chamber participants completed a series of tactically relevant physical exertion tasks involving repeated lift and carry and walking movements. A Rogue Fitness\u0026reg; sandbag (Rogue Fitness, Columbus, OH, USA) was loaded to either 135lbs or 85lbs. Firefighters frequently have to lift, drag, and carry objects of this size during emergency calls [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Participants utilized the 135lb sandbag if their 3-RM deadlift was greater than 175 lbs and deadlift to body weight ratio greater than 1.25. Those that did not meet these criteria used an 85lb sandbag. Participants completed 10 repeated sandbag deadlifts with the prescribed sandbag load. They then lifted a lighter Rogue Fitness\u0026reg; sandbag, loaded to 40lbs to mimic the average weight of a firehose, onto their shoulder and carried it while walking on a treadmill for 0.15 miles. These movements were completed in a circuit twice, before stopping to complete a cognitive assessment (part of the larger study). Participants then completed two additional rounds of the OTA. They were instructed to complete the tasks to the best of their ability and as quickly and safely as possible. Termination criteria included volitional fatigue. Additionally, for the safety of participants, they were removed from the environmental chamber if they reached a core temperature of 39.4\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e2.5.4 Recovery Protocol\u003c/h2\u003e \u003cp\u003eUpon completion of the heat chamber protocol, participants were escorted out of the chamber and into an open area where they removed the helmet, gloves, and turnout jacket and sat in a chair. While recovering they were allowed to roll their pants down below their knees. Boots were kept on mimicking the procedures firefighters follow during emergency call recovery. Participants were provided one bottle of room temperature water to rehydrate. Heart rate, skin temperature, ventilatory rate, and core temperature were monitored continuously during the recovery period. BLC was assessed at immediate post-simulated firefighting, 5-, 10-, 20-, and 40-minute post-OTA.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Physiological Monitoring and Perceived Exertion Measurements\u003c/h2\u003e \u003cp\u003eHeart rate, ventilatory rate, skin temperature, and estimated core temperature were monitored in real-time to assess the physiological stress and intensity of response during the entirety of each trial utilizing the EQ02\u0026thinsp;+\u0026thinsp;LifeMonitor (Equivital EQ02, Hidalgo, UK). A validated heart-rate-derived algorithm [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] is used by the Equivital Black Ghost software to estimate core temperature. This system has recently been shown as a valid alternative to gold-standard rectal temperature monitoring in similar environments and exercise conditions [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. The Equivital measures skin temperature at the torso using an infrared temperature sensor on the back of the Equivital device, which is in contact with the individual's skin, under the individual's arm (at the mid-axillary line of the thorax in line with the individual's xiphoid process of the sternum). BLC was measured before and after AE, RE, CON, and OTA. BLC was also measured during recovery at 5-, 10-, 20-, 30-, and 40-minute timepoints. BLC measurements were obtained using the Nova Biomedical Lactate Plus Meter and procedures outlined above for lactate threshold testing during Day A. The OMNI 0\u0026ndash;10 Rating of Perceived Exertion (RPE) scale was used during acute exercise, at the end of RE sets, at the end of both high and low intervals during AE, and the beginning and end of the control session. The Borg 6\u0026ndash;20 RPE scale [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] was also collected after each OTA task (i.e., sandbag deadlifts and sandbag carry) and every five minutes during recovery. The OMNI scale was used during RE to correlate to the number of Reps in Reserve (RIR) [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e] and provide an accurate training intensity. It was also used during AE, allowing comparisons with RE perceived exertion. However, the Borg scale was used during the OTA because of its correlation to heart rate [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e2.7 Statistical Analysis\u003c/h2\u003e \u003cp\u003eThe Shapiro-Wilks Test, Q-Q plot inspection, and Mauchly\u0026rsquo;s Test was used to evaluate normality and sphericity respectively. First, we conducted a traditional repeated measures ANOVA comparing the total time to complete the OTA by condition. Then conducted an equivalence test for ANOVA to determine if the exercise conditions resulted in practically equivalent changes in time to complete OTA. A practical effect size to determine equivalence bounds was calculated based on the mean difference in time to complete OTA based on the recommendations of the local fire departments on the meaningful difference in time to complete the outlined tasks in an actual occupational scenario. This value was then divided by the pooled standard deviation of time to complete OTA from the actual data collected in this study to obtain a practical effect size, then converted to a partial eta squared (η2p) utilizing the equation provided below.\u003c/p\u003e \u003cp\u003e \u003cem\u003ePractical Effect Size Equation\u003c/em\u003e:\u003c/p\u003e \u003cp\u003e \u003cem\u003eCohen\u0026rsquo;s d\u0026thinsp;=\u0026thinsp;M\u003c/em\u003e \u003csub\u003e \u003cem\u003edifference(estimated)\u003c/em\u003e \u003c/sub\u003e \u003cem\u003e/SD\u003c/em\u003e \u003csub\u003e \u003cem\u003epooled(actual)\u003c/em\u003e \u003c/sub\u003e; \u003cem\u003eCohen\u0026rsquo;s f\u0026thinsp;=\u0026thinsp;d/2; η2p\u0026thinsp;=\u0026thinsp;f\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e/(1\u0026thinsp;+\u0026thinsp;f\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e)\u003c/em\u003e\u003c/p\u003e \u003cp\u003e \u003cem\u003ed\u0026thinsp;=\u0026thinsp;180 sec/((301.62 sec\u0026thinsp;+\u0026thinsp;214.23 sec\u0026thinsp;+\u0026thinsp;261.23 sec)/3) ; f = (0.695/2); η2p\u0026thinsp;=\u0026thinsp;0.348\u003c/em\u003e \u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e/(1\u0026thinsp;+\u0026thinsp;0.348\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e)\u003c/em\u003e\u003c/p\u003e \u003cp\u003eThe equivalence test was completed using the TOSTER package for R to compare the largest effect size observed between exercise conditions against a practical effect size of η2p\u0026thinsp;=\u0026thinsp;0.11 (f\u0026thinsp;=\u0026thinsp;1.382). Additional variables assessed to describe the physiological mechanisms behind performance changes included heart rate, core temperature, skin temperature, ventilatory rate, blood lactate concentration, and rating of perceived exertion (RPE). Average values were calculated based on the minute-to-minute values for heart rate, core temperature, skin temperature, and ventilatory rate during OTA and recovery. Additionally, the time to get to the environmental chamber and put on the firefighter gear (gear time) was compared between AE, RE, and CON to understand differences in the time taken from exercise to OTA. Four-minute averages were calculated for each of these variables for graphic representation and area under the curve (AUC) calculations. The AUC was used as a metric of cumulative heat strain experienced accounting for the maximum temperature reached and the time spent at elevated core temperatures. Five-minute change scores underwent trapezoidal summation to calculate the total AUC for both OTA and recovery. A repeated measures analysis of variance (ANOVA) was performed on average values for each of the measures to determine differences across conditions and recovery. Core temperature was the only peak value assessed due to its relation to exertional heat illness risk [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. Other peak values were not assessed to reduce the risk of type I error from multiple testing. Equivalence tests were not used for variables other than time to complete because it is unclear what a practically significant difference for these physiological variables would be. For any significant main effects detected, post hoc comparisons with Bonferroni adjustments were utilized for multiple comparisons. If sphericity was violated, statistical interpretations were made utilizing Greenhouse-Geisser adjusted degrees of freedom. Data is expressed as mean \u0026plusmn; standard deviation. Significance in this investigation was set a priori at a p-value \u0026le; 0.05 for all measurements. R Statistical Programming Software Version 4.1.2 (RStudio; Boston, MA) was used for all statistical analyses [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. The application, G*Power, was utilized a priori to determine a sample size of 28 total participants necessary for a sufficiently powered study. To estimate sample size the following values were used: test family\u0026thinsp;=\u0026thinsp;F tests, repeated measures ANOVA, one group, three measurements, correlation among repeated measures\u0026thinsp;=\u0026thinsp;0.5, non-sphericity correction ε\u0026thinsp;=\u0026thinsp;1.0, α\u0026thinsp;=\u0026thinsp;0.05, 1-β\u0026thinsp;=\u0026thinsp;0.80, η2p\u0026thinsp;=\u0026thinsp;0.06. Effect size classifications included a small effect (η2p\u0026thinsp;=\u0026thinsp;0.010\u0026ndash;0.059), moderate effect (η2p\u0026thinsp;=\u0026thinsp;0.060\u0026ndash;0.139), and large effect (η2p\u0026thinsp;\u0026gt;\u0026thinsp;0.14). This effect size was determined based on previous research observing effect sizes from 0.01\u0026ndash;0.56 with similar outcomes [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"3 RESULTS","content":"\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Baseline Values\u003c/h2\u003e \u003cp\u003ePre-trial USG (F(2, 62)\u0026thinsp;=\u0026thinsp;0.752; p\u0026thinsp;=\u0026thinsp;0.475, η2p\u0026thinsp;=\u0026thinsp;0.02) and Pre-BLC (F(2, 62)\u0026thinsp;=\u0026thinsp;0.281; p\u0026thinsp;=\u0026thinsp;0.281, η2p\u0026thinsp;=\u0026thinsp;0.04) were not significantly different. Full demographic information can be found in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eParticipant demographics\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eVariable\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eN\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eMin \u0026ndash; Max [Range]\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (yrs)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOverall\u003c/p\u003e \u003cp\u003eFemale\u003c/p\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32\u003c/p\u003e \u003cp\u003e15\u003c/p\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25.19\u0026thinsp;\u0026plusmn;\u0026thinsp;4.12\u003c/p\u003e \u003cp\u003e26.07\u0026thinsp;\u0026plusmn;\u0026thinsp;4.17\u003c/p\u003e \u003cp\u003e24.41\u0026thinsp;\u0026plusmn;\u0026thinsp;4.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e19.00\u0026ndash;35.00 [16.00]\u003c/p\u003e \u003cp\u003e20.00\u0026ndash;35.00 [15.00]\u003c/p\u003e \u003cp\u003e19.00\u0026ndash;31.00 [12.00]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeight (cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOverall\u003c/p\u003e \u003cp\u003eFemale\u003c/p\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32\u003c/p\u003e \u003cp\u003e15\u003c/p\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e173.78\u0026thinsp;\u0026plusmn;\u0026thinsp;9.84\u003c/p\u003e \u003cp\u003e165.23\u0026thinsp;\u0026plusmn;\u0026thinsp;5.73\u003c/p\u003e \u003cp\u003e181.34\u0026thinsp;\u0026plusmn;\u0026thinsp;5.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e153.50\u0026ndash;193.00 [39.50]\u003c/p\u003e \u003cp\u003e153.50\u0026ndash;175.30 [21.80]\u003c/p\u003e \u003cp\u003e171.50\u0026ndash;193.00 [21.50]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWeight (kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOverall\u003c/p\u003e \u003cp\u003eFemale\u003c/p\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32\u003c/p\u003e \u003cp\u003e15\u003c/p\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e75.57\u0026thinsp;\u0026plusmn;\u0026thinsp;13.22\u003c/p\u003e \u003cp\u003e64.47\u0026thinsp;\u0026plusmn;\u0026thinsp;6.53\u003c/p\u003e \u003cp\u003e85.36\u0026thinsp;\u0026plusmn;\u0026thinsp;9.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e52.40\u0026ndash;103.00 [50.60]\u003c/p\u003e \u003cp\u003e52.40\u0026ndash;76.30 [23.90]\u003c/p\u003e \u003cp\u003e66.80\u0026ndash;103.00 [36.20]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBody Fat Percentage\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOverall\u003c/p\u003e \u003cp\u003eFemale\u003c/p\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32\u003c/p\u003e \u003cp\u003e15\u003c/p\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e23.28\u0026thinsp;\u0026plusmn;\u0026thinsp;7.43\u003c/p\u003e \u003cp\u003e27.80\u0026thinsp;\u0026plusmn;\u0026thinsp;6.19\u003c/p\u003e \u003cp\u003e19.29\u0026thinsp;\u0026plusmn;\u0026thinsp;6.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11.00\u0026ndash;43.60 [32.60]\u003c/p\u003e \u003cp\u003e20.30\u0026ndash;43.60 [23.30]\u003c/p\u003e \u003cp\u003e11.00\u0026ndash;38.10 [27.10]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVO2max (mL/kg/min)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOverall\u003c/p\u003e \u003cp\u003eFemale\u003c/p\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32\u003c/p\u003e \u003cp\u003e15\u003c/p\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e46.15\u0026thinsp;\u0026plusmn;\u0026thinsp;7.43\u003c/p\u003e \u003cp\u003e42.14\u0026thinsp;\u0026plusmn;\u0026thinsp;5.78\u003c/p\u003e \u003cp\u003e49.68\u0026thinsp;\u0026plusmn;\u0026thinsp;7.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e31.20\u0026ndash;62.60 [31.40]\u003c/p\u003e \u003cp\u003e32.50\u0026ndash;50.60 [18.10]\u003c/p\u003e \u003cp\u003e31.20\u0026ndash;62.60 [31.40]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProjected 1-RM Squat (kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOverall\u003c/p\u003e \u003cp\u003eFemale\u003c/p\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32\u003c/p\u003e \u003cp\u003e15\u003c/p\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e108.21\u0026thinsp;\u0026plusmn;\u0026thinsp;38.37\u003c/p\u003e \u003cp\u003e80.24\u0026thinsp;\u0026plusmn;\u0026thinsp;15.19\u003c/p\u003e \u003cp\u003e133.32\u0026thinsp;\u0026plusmn;\u0026thinsp;35.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e56.25\u0026ndash;224.53 [168.28]\u003c/p\u003e \u003cp\u003e56.36\u0026ndash;105.00 [48.64]\u003c/p\u003e \u003cp\u003e73.18\u0026thinsp;\u0026plusmn;\u0026thinsp;225.00 [151.82]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProjected 1-RM Bench (kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOverall\u003c/p\u003e \u003cp\u003eFemale\u003c/p\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32\u003c/p\u003e \u003cp\u003e15\u003c/p\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e77.14\u0026thinsp;\u0026plusmn;\u0026thinsp;36.04\u003c/p\u003e \u003cp\u003e46.24\u0026thinsp;\u0026plusmn;\u0026thinsp;11.94\u003c/p\u003e \u003cp\u003e104.71\u0026thinsp;\u0026plusmn;\u0026thinsp;26.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e26.76\u0026ndash;142.88 [116.12]\u003c/p\u003e \u003cp\u003e26.82\u0026ndash;68.64 [41.82]\u003c/p\u003e \u003cp\u003e51.36\u0026ndash;143.18 [91.82]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProjected 1-RM Deadlift (kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOverall\u003c/p\u003e \u003cp\u003eFemale\u003c/p\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32\u003c/p\u003e \u003cp\u003e15\u003c/p\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e119.04\u0026thinsp;\u0026plusmn;\u0026thinsp;42.27\u003c/p\u003e \u003cp\u003e87.67\u0026thinsp;\u0026plusmn;\u0026thinsp;20.55\u003c/p\u003e \u003cp\u003e147.19\u0026thinsp;\u0026plusmn;\u0026thinsp;36.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e58.97\u0026ndash;221.81 [162.84]\u003c/p\u003e \u003cp\u003e59.09\u0026ndash;124.55 [65.45]\u003c/p\u003e \u003cp\u003e95.91\u0026ndash;221.27 [146.36]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003eValues Reported as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation. M\u0026thinsp;=\u0026thinsp;males, F\u0026thinsp;=\u0026thinsp;females; 1-RM\u0026thinsp;=\u0026thinsp;1 repetition maximum.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e(Insert\u003c/b\u003e Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Acute Exercise Intensity\u003c/h2\u003e \u003cp\u003eAverage heart rate (F(2, 62)\u0026thinsp;=\u0026thinsp;395.57; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η2p\u0026thinsp;=\u0026thinsp;0.93), core temperature (F(2, 62)\u0026thinsp;=\u0026thinsp;132.16; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η2p\u0026thinsp;=\u0026thinsp;0.81), skin temperature (F(2, 62)\u0026thinsp;=\u0026thinsp;34.70; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η2p\u0026thinsp;=\u0026thinsp;0.53), ventilatory rate (F(2, 62)\u0026thinsp;=\u0026thinsp;160.68; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η2p\u0026thinsp;=\u0026thinsp;0.84) were all significantly higher following AE and RE compared to CON. Additionally, Post-exercise BLC (F(2, 62)\u0026thinsp;=\u0026thinsp;102.36; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η2p\u0026thinsp;=\u0026thinsp;0.77) was all significantly higher following AE and RE compared to CON. Average heart rate (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and ventilatory rate (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) were significantly higher during AE compared to RE. BLC (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.000), core temperature (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.000), and skin temperature (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.000) did not significantly differ between AE and RE. Duration of exercise session was significantly different between conditions (F(2,62)\u0026thinsp;=\u0026thinsp;60.04; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η2p\u0026thinsp;=\u0026thinsp;0.66). Post-hoc analysis suggests that RE duration was significantly longer than AE and CON (\u003cem\u003eps\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and AE duration was significantly longer than CON (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The gear time or time to transition from acute exercise, don firefighter gear and start the OTA was significantly different between conditions (CON: 6.03\u0026thinsp;\u0026plusmn;\u0026thinsp;1.79, AE: 6.00\u0026thinsp;\u0026plusmn;\u0026thinsp;1.51; RE: 8.81\u0026thinsp;\u0026plusmn;\u0026thinsp;2.19; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001). Post-hoc analysis suggests the RE gear time was significantly longer than AE and CON (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001). full report including mean and standard deviations of average as well as peak values for each of these variables can be found in Tables\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExercise prescription values\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eAerobic Session\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003e\u003cem\u003eLow Interval\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e\u003cem\u003eHigh Interval\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRPE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003e3.86\u0026thinsp;\u0026plusmn;\u0026thinsp;1.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e8.32\u0026thinsp;\u0026plusmn;\u0026thinsp;1.11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpeed (km/h)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003e6.98\u0026thinsp;\u0026plusmn;\u0026thinsp;1.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e19.78\u0026thinsp;\u0026plusmn;\u0026thinsp;2.99\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eResistance Session\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eSquat\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eBench\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e\u003cem\u003eDeadlift\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003eBent Row\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRPE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.86\u0026thinsp;\u0026plusmn;\u0026thinsp;1.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e8.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e7.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReps\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e5.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLoad (kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e191.15\u0026thinsp;\u0026plusmn;\u0026thinsp;66.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e135.21\u0026thinsp;\u0026plusmn;\u0026thinsp;63.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e206.72\u0026thinsp;\u0026plusmn;\u0026thinsp;73.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e109.48\u0026thinsp;\u0026plusmn;\u0026thinsp;44.70\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003eRPE\u0026thinsp;=\u0026thinsp;Rating of Perceived Exertion (OMNI 0\u0026ndash;10 scale) *Denote significantly different than control session; \u003csup\u003e\u0026dagger;\u003c/sup\u003e Denotes significantly different than aerobic session. Statistical significance was set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhysiological response to acute exercise\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eVariable\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eControl Session\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eAerobic Exercise\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eResistance Exercise\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePeak HR (bpm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e105.53\u0026thinsp;\u0026plusmn;\u0026thinsp;20.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e185.81\u0026thinsp;\u0026plusmn;\u0026thinsp;10.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e172.22\u0026thinsp;\u0026plusmn;\u0026thinsp;19.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAvg HR (bpm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e74.07\u0026thinsp;\u0026plusmn;\u0026thinsp;17.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e144.05\u0026thinsp;\u0026plusmn;\u0026thinsp;8.43*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e127.40\u0026thinsp;\u0026plusmn;\u0026thinsp;19.62*\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePeak VE (brpm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24.88\u0026thinsp;\u0026plusmn;\u0026thinsp;6.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50.59\u0026thinsp;\u0026plusmn;\u0026thinsp;7.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e37.78\u0026thinsp;\u0026plusmn;\u0026thinsp;7.21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAvg VE (brpm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15.54\u0026thinsp;\u0026plusmn;\u0026thinsp;6.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33.79\u0026thinsp;\u0026plusmn;\u0026thinsp;4.71*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e27.08\u0026thinsp;\u0026plusmn;\u0026thinsp;4.08*\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePeak ST (\u0026deg;C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e34.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36.61\u0026thinsp;\u0026plusmn;\u0026thinsp;0.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e35.88\u0026thinsp;\u0026plusmn;\u0026thinsp;2.11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAvg ST (\u0026deg;C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e33.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e34.65\u0026thinsp;\u0026plusmn;\u0026thinsp;1.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e34.71\u0026thinsp;\u0026plusmn;\u0026thinsp;1.26\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePeak CT (\u0026deg;C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e37.08\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e38.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e38.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAvg CT (\u0026deg;C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e37.79\u0026thinsp;\u0026plusmn;\u0026thinsp;0.41\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePost-BLC (mMol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8.31\u0026thinsp;\u0026plusmn;\u0026thinsp;2.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.41\u0026thinsp;\u0026plusmn;\u0026thinsp;3.35\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDuration (minutes)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26.97\u0026thinsp;\u0026plusmn;\u0026thinsp;1.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e36.72\u0026thinsp;\u0026plusmn;\u0026thinsp;6.09\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003eBpm\u0026thinsp;=\u0026thinsp;Beats/minute; Brpm\u0026thinsp;=\u0026thinsp;breaths/minute; \u0026deg;C\u0026thinsp;=\u0026thinsp;degrees Celsius; mMol\u0026thinsp;=\u0026thinsp;milliMol/Liter; *Denotes significantly different than control session; \u003csup\u003e\u0026dagger;\u003c/sup\u003e Denotes significantly different than aerobic session. Statistical significance was set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e(Insert\u003c/b\u003e Tables\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Occupational Task Assessment Results\u003c/h2\u003e \u003cp\u003eAverage time to complete was 1133.62\u0026thinsp;\u0026plusmn;\u0026thinsp;261.62 sec after CON compared to 1197.83\u0026thinsp;\u0026plusmn;\u0026thinsp;214.23 sec after AE and 1211.48\u0026thinsp;\u0026plusmn;\u0026thinsp;301.62 sec after RE. ANOVA results suggest that there was not as significant difference between pre-OTA conditions (F(2,54)\u0026thinsp;=\u0026thinsp;1.88; p\u0026thinsp;=\u0026thinsp;0.162; η2p\u0026thinsp;=\u0026thinsp;0.07). Based on our equivalence test, we rejected the presence of effects in time to complete OTA between conditions more extreme than η2p\u0026thinsp;=\u0026thinsp;0.11, or 3 minutes (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.014). Visual representation of the average time to complete the OTA between conditions can be found in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e(Insert\u003c/b\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e\u003c/p\u003e \u003cp\u003eHeart rate (F(2, 62)\u0026thinsp;=\u0026thinsp;47.04; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η2p\u0026thinsp;=\u0026thinsp;0.60), core temperature (F(2, 62)\u0026thinsp;=\u0026thinsp;195.00; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001; η2p\u0026thinsp;=\u0026thinsp;0.86), skin temperature (F(2, 62)\u0026thinsp;=\u0026thinsp;38.69; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001; η2p\u0026thinsp;=\u0026thinsp;0.56), and ventilatory rate (F(2, 62)\u0026thinsp;=\u0026thinsp;7.98; \u003cem\u003ep\u0026thinsp;\u0026lt;\u003c/em\u003e\u0026thinsp;0.001; η2p\u0026thinsp;=\u0026thinsp;0.21) were all significantly different between conditions during OTA. BLC immediate-post OTA was not significantly different (F(1, 62)\u0026thinsp;=\u0026thinsp;2.794; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.072; η2p\u0026thinsp;=\u0026thinsp;0.09). Post hoc analysis revealed heart rate during the OTA was significantly higher following AE and RE compared to CON and significantly lower after RE compared to AE (\u003cem\u003eps\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.002). Core temperature was significantly higher during OTA following RE and AE compared to CON, and RE was significantly lower than AE (\u003cem\u003eps\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.002). Skin temperature was significantly higher during OTA following AE and RE compared to CON, and RE was also significantly lower than AE (\u003cem\u003eps\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Ventilatory rate was significantly higher during OTA following AE and RE compared to CON (\u003cem\u003eps\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.004), but AE was not different from RE (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.000). When comparing peak physiological response experienced, max core temperature was significantly different by condition (F(2, 62)\u0026thinsp;=\u0026thinsp;102.12; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η2p\u0026thinsp;=\u0026thinsp;0.77). Post-hoc analysis indicated max core temperature was significantly higher following AE compared to both CON (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and RE (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.002) and RE was significantly higher than CON (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eAverage RPE was significantly different by condition (F(2, 62)\u0026thinsp;=\u0026thinsp;26.83; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001; η2p\u0026thinsp;=\u0026thinsp;0.46). Post hoc analysis revealed RPE during OTA was significantly higher following AE and RE compared to CON (\u003cem\u003eps\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001), but not significantly different between AE and RE (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.000). Additionally, gear time (time between acute exercise and OTA) was significantly longer (F(2, 56)\u0026thinsp;=\u0026thinsp;31.55; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η2p\u0026thinsp;=\u0026thinsp;0.53). Post-hoc analysis showed gear time was significantly longer following RE compared to AE and CON (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001), but AE was not significantly different from CON (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.000). AUC (cumulative heat stress experienced during OTA) was significantly different by condition (F(2, 60)\u0026thinsp;=\u0026thinsp;15.66; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001, η2p\u0026thinsp;=\u0026thinsp;0.34). Post-hoc analysis revealed AUC was significantly higher following AE and RE compared to CON (\u003cem\u003eps\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.010), but not different between AE and RE (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.092). Mean and standard deviations for average in these physiological variables and perception of exertion can be found in Tables\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Pre- to post-OTA blood lactate concentrations are visually represented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Graphs highlighting the rate of increase in these physiological variables can be found in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhysiological response and perceived exertion during OTA\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eVariable\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eControl\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eAerobic Exercise\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eResistance Exercise\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage Heart Rate (bpm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e148.49\u0026thinsp;\u0026plusmn;\u0026thinsp;16.22\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e166.28\u0026thinsp;\u0026plusmn;\u0026thinsp;11.47*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e159.91\u0026thinsp;\u0026plusmn;\u0026thinsp;12.99*\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage Ventilation Rate (brpm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e37.19\u0026thinsp;\u0026plusmn;\u0026thinsp;4.78\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40.24\u0026thinsp;\u0026plusmn;\u0026thinsp;6.58*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e39.69\u0026thinsp;\u0026plusmn;\u0026thinsp;5.49*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage Skin Temperature (\u0026deg;C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.54\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e36.87\u0026thinsp;\u0026plusmn;\u0026thinsp;0.86*\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage Core Temperature (\u0026deg;C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e37.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e38.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e38.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46*\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePre-Chamber BLC (mMol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.54\u0026thinsp;\u0026plusmn;\u0026thinsp;0.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.13\u0026thinsp;\u0026plusmn;\u0026thinsp;2.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.15\u0026thinsp;\u0026plusmn;\u0026thinsp;2.65\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePost Chamber BLC (mMol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.85\u0026thinsp;\u0026plusmn;\u0026thinsp;3.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.10\u0026thinsp;\u0026plusmn;\u0026thinsp;2.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.58\u0026thinsp;\u0026plusmn;\u0026thinsp;3.71\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage RPE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12.72\u0026thinsp;\u0026plusmn;\u0026thinsp;1.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.27\u0026thinsp;\u0026plusmn;\u0026thinsp;1.56*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.69\u0026thinsp;\u0026plusmn;\u0026thinsp;1.62*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003eBpm\u0026thinsp;=\u0026thinsp;Beats/minute; Brpm\u0026thinsp;=\u0026thinsp;breaths/minute; \u0026deg;C\u0026thinsp;=\u0026thinsp;degrees Celsius; RPE\u0026thinsp;=\u0026thinsp;Rating of Perceived Exertion (Borg 6\u0026ndash;20) *Denotes significantly different than control session; \u003csup\u003e\u0026dagger;\u003c/sup\u003e Denotes significantly different than aerobic session. Statistical significance was set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e(Insert\u003c/b\u003e Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026thinsp;\u003cb\u003e+\u003c/b\u003e\u0026thinsp;Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Recovery Responses\u003c/h2\u003e \u003cp\u003eDuring recovery, there were not statistically significant differences in average heart rate (F(2, 62)\u0026thinsp;=\u0026thinsp;1.17; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.318; η2p\u0026thinsp;=\u0026thinsp;0.04), core temperature (F(2, 62)\u0026thinsp;=\u0026thinsp;1.85; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.165; η2p\u0026thinsp;=\u0026thinsp;0.06), skin temperature (F(2, 62)\u0026thinsp;=\u0026thinsp;0.10; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.905; η2p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), ventilatory rate (F(2, 62)\u0026thinsp;=\u0026thinsp;0.49; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.618; η2p\u0026thinsp;=\u0026thinsp;0.02), or change in BLC (F(2, 62)\u0026thinsp;=\u0026thinsp;1.84; p\u0026thinsp;=\u0026thinsp;0.168; η2p\u0026thinsp;=\u0026thinsp;0.06). There was a significant difference in AUC between conditions (F(2, 62)\u0026thinsp;=\u0026thinsp;70.94; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001; η2p\u0026thinsp;=\u0026thinsp;0.70). Post hoc analysis indicated CON recovery AUC was significantly lower than AE and RE (\u003cem\u003eps\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.001), but AE and RE were not significantly different (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.630). A visual representation of the rate of recovery for these variables are included in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e(Insert\u003c/b\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e\u003c/p\u003e \u003c/div\u003e"},{"header":"4 DISCUSSION","content":"\u003cp\u003eNFPA recommends firefighters exercise on-shift [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. Previous research suggests firefighters frequently have on-site access to barbells and treadmills allowing them to complete both aerobic and resistance exercise on shift [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. However, firefighters have expressed concerns that exercising on-shift may decrease their ability to respond to emergency calls, making it important to understand the impact acute on-shift exercise has on firefighter occupational performance. Therefore, this study aimed to determine if resistance or aerobic training impacts occupational performance and physiological strain.\u003c/p\u003e \u003cp\u003eContrary to our primary hypothesis, we did not find evidence that exercise modality impacted occupational performance, despite finding evidence of elevated markers of physiological and perceptual strain (elevated skin temperature, core temperature, heart rate, and RPE) in both AE and RE conditions compared to CON. These findings differed from previous research investigating the effect of acute exercise on occupational performance [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Methodological differences likely contributed to the differences in findings. The aim of both previous investigations involved an acute exercise prescription of high-intensity circuit-style resistance training [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. This has good application, as many firefighters currently engage in this form of exercise training. Our study aimed to add to these findings through the comparison of conventional resistance exercises and high-intensity interval training (HIIT), to help elucidate how the two exercise stressors may impact occupational performance differently. The divergence in findings may also relate to the circuit-style fashion, which can replicate more similar demands (repeated lifting and moving tasks with minimal rest) resulting in fatigue of the same musculature and depletion of the same substrates utilized during occupational tasks to a greater degree than resistance or aerobic exercise, therefore leading to larger interference with occupational performance. Taken together, these finding provide a more comprehensive understanding of how different training methods may have unique impacts on occupational performance.\u003c/p\u003e \u003cp\u003eCore temperature, heart rate, and skin temperature were all elevated in the acute exercise conditions when compared to CON and elevated the most following AE even though numerically higher RPE and time to complete occupational tasks was ~\u0026thinsp;30 sec slower following RE. An elevated core temperature following an acute bout of aerobic exercise could potentially limit a firefighter\u0026rsquo;s ability to continue work during extended operations (longer than the average 20 minutes experienced in this study), possibly putting firefighters at an increased risk for fatigue and exertional heat injury [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. This is already a primary concern of fire services [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e], with almost 75% of firefighters experiencing heat injury symptoms in a calendar year [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]. These elevated physiological responses warrant future investigations involving longer occupational task assessments to further elucidate this risk.\u003c/p\u003e \u003cp\u003eParticipants in our study did not use a SCBA during our investigation, because firefighters would not utilize a SCBA during the operations we intended to replicate, However, ventilatory rates were investigated because of the relationship between breathing rate, oxygen consumption, and the depletion of the air experienced when a firefighter is using a self-contained breathing apparatus (SCBA). Previous research has shown that acute exercise 10 minutes before an occupational task assessment, but not 60 minutes prior, increased air depletion [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Our results indicate ventilatory rates were significantly higher during acute exercise (AE and RE) compared to CON. This may suggest prior acute exercise may influence SCBA depletion rate. However, this is speculative as we did not assess the SCBA depletion in this study.\u003c/p\u003e \u003cp\u003eUnlike the previously mentioned variables, BLC was not significantly different between conditions, possibly due to the use of a high-intensity interval-based aerobic workout. A long, slow continuous aerobic workout may have resulted in lower lactate levels going into the OTA, resulting in lower post-OTA BLC. An interesting observation was that participants, on average, experienced almost no change (0.03 mMol/L decrease) in BLC following AE; while there was a 2.4 mMol/L increase following RE. This could be a result of increased reliance on rapid glycolysis aerobic metabolism and subsequently higher lactate accumulation during the OTA following RE, compared to AE. This difference was not statistically significant, although there was a moderate effect (η2p\u0026thinsp;=\u0026thinsp;0.09). This warrants future investigations into lactate response and its influence on occupational demands, specifically in higher intensity or even longer duration tasks where lactate levels may limit performance.\u003c/p\u003e \u003cp\u003eWhen considering the physiological responses experienced it is worth considering the average time to complete the tasks and the type of tasks completed in this study compared to previous work. In previous investigations, the times to complete occupational tasks were ~\u0026thinsp;7 minutes or less [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], while we aimed to understand acute exercise\u0026rsquo;s impact on extended occupational tasks (~\u0026thinsp;20 minutes in duration). Taken with the physiological variables measured across our study and previous work we can reasonably consider that acute exercise may decrease performance of short, high-intensity occupational demands through increased fatigue from acidosis; while increasing heat injury risk during longer, moderately high-intensity tasks due to increases in core temperature. This is supported by the lower levels of blood lactate concentrations following our occupational tasks compared to previous studies [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] and elevated core temperatures observed in the current investigation. While the current and previous investigations provide an understanding of acute exercise\u0026rsquo;s impact on both short and moderate duration occupational tasks [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], firefighting scenarios can extend to longer durations. When considering a firefighter\u0026rsquo;s SCBA lasts on average 30\u0026ndash;60 min [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e] and it worth investigating occupational scenarios of this duration in future work. In addition to the increased physiological strain experienced during the OTA, perceived exertion was elevated following both RE and AE when compared to CON. This could likely be a consequence of the elevated core temperature and skin temperature increasing thermal stress, resulting in the OTA feeling more demanding even though participants were able to complete the tasks at the same rate.\u003c/p\u003e \u003cp\u003eAcute exercise bouts did not impair the rate at which participants recovered following occupational task performance, contrary to our secondary hypothesis. We hypothesized aerobic exercise would have a slower rate of recovery following the OTA due to the added volume of exertion from acute exercise. Yet, our findings indicate heart rate, core temperature, skin temperature, ventilatory rate, and blood lactate concentrations were not significantly different on average or at the end of the 40-minute recovery. However, AUC between conditions was elevated during recovery from AE and RE. This suggests the individuals\u0026rsquo; core temperature spent a larger portion of the recovery at an elevated level. There may have been elevated fatigue or thermal stress experienced that was not accounted for in the current investigation, even though participants returned to similar resting values. This could impact subsequent occupational readiness for future calls during their shift.\u003c/p\u003e \u003cp\u003eAn important limitation of this study to note is the choice to use members of the community rather than current firefighters. We acknowledge that firefighters have unique experiences working in the heat [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e], and previous research has suggested that long-term, career firefighters do experience specific heat adaptations that may differ from the experiences of the population sampled in the current investigation [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]. Additionally, previous literature suggests that firefighters are on average older and have poorer cardiovascular outcomes [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e] than our relatively young and healthy sample which may impact the responses seen. However, this was an intentional decision as the local fire departments in our area are younger [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e] and more physically active [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] than the national average, similar to the sample presented in our investigation. Therefore, when considering this and the limited number of local firefighters and more specifically female firefighters the use of local community ensured an adequate and diverse sample population. This population also aids in understanding the responses experienced by new firefighters that have not yet experienced these adaptations. Additionally, the movements chosen for the OTA in this study were based on recommendations of the local fire department, which were limited based on the confines of our environmental chamber and do not represent all firefighting task demands. We also did not measure thermal sensation, which would have provided supplemental information to help understand potential behavioral thermoregulatory measures (i.e., slowing pace down or stopping between tasks) that may have been impacted by an acute exercise bout. Lastly, the gear time was ~\u0026thinsp;2\u0026ndash;3 minutes longer following the resistance training session compared to aerobic and resting control partly due to the location of our weight room being further from our environmental chamber than our aerobic and control testing area. This gear time was not standardized as we wanted to replicate immediate post-exercise conditions with no rest. While this difference could have had a small impact on OTA responses; had we standardized the rest period, the participants would have had 2\u0026ndash;3 minutes of passive rest prior to entering the chamber after the aerobic and resting control conditions, which would have likely had a larger impact on OTA responses.\u003c/p\u003e \u003cp\u003eThe current study sought to determine immediate decrements from acute exercise on occupational performance. However, if the call comes in hours after on-shift exercise fatigue, delayed onset muscle soreness, and other factors may differentially influence occupational readiness. One study aimed to address the difference between a 10-minute and 60-minute post-exercise occupational task assessment. The findings suggested that while there were impairments at 10-minutes, they were statistically recovered by 60-minutes post-exercise [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The potential for an emergency call to arrive at any time during their work shift warrants further investigation into the time course of the impact of acute exercise on occupational tasks. In addition to the considerations of on-shift exercise, off-shift exercise presents its own considerations in future research, specifically for factors related to substrate availability and delayed on-set muscle soreness. Lastly, we chose conventional strength training and high-intensity interval training based on the common equipment resources accessible [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] and preferred methods of aerobic training of firefighters as well as the demand for both strength and aerobic capacity in firefighters. However, there are a multitude of different exercise prescription choices that could influence the acute response to exercise (i.e., sets, reps, intensity, rest intervals, and movements chosen) that should be investigated in the future to fully understand prescription recommendations to optimize improvements in occupationally relevant fitness while minimizing decrements in occupational readiness in fire services.\u003c/p\u003e"},{"header":"5 CONCLUSIONS","content":"\u003cp\u003eThe data presented suggest a firefighter may be able to exercise while on-shift and respond to a call without meaningful decrements in performance. However, these potential increases in physiological strain provide precautionary data that individual\u0026rsquo;s may be at an increased risk of overexertion or heat-related injury while completing occupational tasks if they exercised immediately beforehand. This risk may be even higher after aerobic exercise even though rating of perceived exertion, post-OTA blood lactate concentrations, and time to complete were numerically higher after resistance exercise. Fire departments and fitness professionals working with fire services can utilize these findings to guide training programs. With the knowledge that aerobic fitness and muscular strength are required for this population to meet the demands of their occupations, it is important we understand how to address fitness most effectively and efficiently without interfering with their occupational readiness. Even though there was a larger numeric decrease in time to complete occupational tasks when resistance exercise was performed prior (2.5% longer than when aerobic exercise was performed), the risk for heat related illness is a more important consideration for fire services. Therefore, it may be beneficial for fire service strength and conditioning professionals to prescribe aerobic exercise off-shift and focus on resistance exercise on-shift to minimize heat illness while still working toward improvements in fitness through the implementation of on-shift exercise. However, limitations related to adherence to unsupervised exercise may make this difficult. If aerobic exercise is performed on-shift, firefighters should be aware of the potential increased risks, and take precautions including the utilization of cooling methods to mitigate this increase during exercise.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eWe have no funding sources to declare for this study.\u003c/p\u003e\u003cp\u003e \u003ch2\u003eConsent to participate\u003c/h2\u003e \u003cp\u003e Informed consent was obtained from all individual participants included in the study.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eEthical Approval\u003c/strong\u003e \u003cp\u003e The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board (or Ethics Committee) of Auburn University (protocol code #22\u0026ndash;149 MR 2205, 05/05/2022).\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConflict of Interest\u003c/strong\u003e \u003cp\u003eThe authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding Sources\u003c/h2\u003e \u003cp\u003eThe authors declare no funding was received for this project.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization, PJA, JMS, CBM, MWM, WMM; Data curation, PJA and NCB; Formal analysis, PA.; Investigation PJA, NCB, PLJ, AMR., LFR; Methodology, PJA, JMS, CBM, MWM, WMM; Project administration, PJA, NCB, PLJ, AMR, LFR; Supervision, JMS; Visualization, PJA; Writing\u0026mdash;original draft, PJA, NCB; Writing\u0026mdash;review and editing, all authors.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe would like to thank our research volunteers for assisting with data collection, and the participants for their time and efforts.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eCarballo-Leyenda, B., et al., \u003cem\u003eWildland firefighters\u0026rsquo; thermal exposure in relation to suppression tasks\u003c/em\u003e. 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Journal of Athletic Training, 2020. 55(1): p. 71\u0026ndash;79.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Environmental Stress, Occupational Stress, Fire Services, Strength Training, Endurance Training, HIIT","lastPublishedDoi":"10.21203/rs.3.rs-4547891/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4547891/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eWe aimed to determine how a bout of resistance or aerobic exercise impacts physiological responses and performance during firefighting occupational tasks.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eThirty-two non-firefighters completed two baseline assessments, and three trials: resistance exercise (RE), aerobic exercise (AE), or rested control (CON). Trials were followed by an occupational task assessment (OTA; four rounds of 10 deadlifts (85 or 135lbs) and 0.15-mile 40lb-sandbag carry) in an environmental chamber (35\u0026deg;C/50% humidity).\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eTime to complete by condition was not statistically different (CON: 1134\u0026thinsp;\u0026plusmn;\u0026thinsp;261, AE: 1198\u0026thinsp;\u0026plusmn;\u0026thinsp;214, RE: 1212\u0026thinsp;\u0026plusmn;\u0026thinsp;302 sec; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.162). Average heart rate (CON: 148.5\u0026thinsp;\u0026plusmn;\u0026thinsp;16.2, AE: 166.3\u0026thinsp;\u0026plusmn;\u0026thinsp;11.5, RE: 159.9\u0026thinsp;\u0026plusmn;\u0026thinsp;13.0 bpm; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), core temperature (CON: 37.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35, AE: 38.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26, RE: 38.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46\u0026deg;C; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), and skin temperature (CON: 36.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.54, AE: 37.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58, RE: 36.87\u0026thinsp;\u0026plusmn;\u0026thinsp;0.86\u0026deg;C; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01) were elevated during OTA following AE and RE compared to CON, and higher following AE compared to RE.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eOur findings suggest job performance may not be impacted, physiological strain during the tasks may be elevated; increasing risk for heat injury following on-shift exercise, and more prominently following aerobic exercise.\u003c/p\u003e","manuscriptTitle":"Impact of acute exercise on performance and physiological stress during simulated firefighter occupational tasks","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-16 11:51:23","doi":"10.21203/rs.3.rs-4547891/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-09-11T20:21:29+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-11T16:45:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"295620787111666869860886317322866921861","date":"2024-08-14T18:09:07+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-12T22:54:39+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"8507818272719716394947939651141941092","date":"2024-08-09T18:37:25+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-08-09T17:47:44+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-08-01T16:47:41+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-06-25T16:01:34+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-06-25T04:18:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-06-07T19:43:47+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"eee223c7-1789-42bc-b0b7-b03dfcfd24b2","owner":[],"postedDate":"July 16th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":34433845,"name":"Biological sciences/Physiology"},{"id":34433846,"name":"Health sciences/Health occupations"}],"tags":[],"updatedAt":"2024-12-02T17:24:30+00:00","versionOfRecord":{"articleIdentity":"rs-4547891","link":"https://doi.org/10.1038/s41598-024-81015-8","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2024-11-30 15:58:34","publishedOnDateReadable":"November 30th, 2024"},"versionCreatedAt":"2024-07-16 11:51:23","video":"","vorDoi":"10.1038/s41598-024-81015-8","vorDoiUrl":"https://doi.org/10.1038/s41598-024-81015-8","workflowStages":[]},"version":"v1","identity":"rs-4547891","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4547891","identity":"rs-4547891","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}