Effects of 4-week high intensity interval training on anaerobic capacity, repeated-sprints performance and neuromuscular function

Effects of 4-week high intensity interval training on anaerobic capacity, repeated-sprints performance and neuromuscular function | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effects of 4-week high intensity interval training on anaerobic capacity, repeated-sprints performance and neuromuscular function Fabio Milioni, Guillaume Millet, Rodrigo Araújo Bonetti de Poli, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3897583/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Purpose: High-intensity long-interval training (long-HIIT; interval≥1 min; intensity 85%-100% of maximal oxygen uptake [V̇O 2 max]) is often applied for cardiorespiratory adaptations, however long-HIIT can also challenge the anaerobic and neuromuscular systems. Therefore, this study aimed to investigate the effects of 4-week long-HIIT (11 sessions) on anaerobic capacity, repeated sprint ability (RSA), and neuromuscular function. Methods: Twenty active men (V̇O 2 max: 44.8±5.3 mL.kg -1 .min -1 ) performed an incremental running test (T INC ), a supramaximal test consisting in running until the task failure at 115% of maximum velocity achieved in T INC (V INC ) for anaerobic capacity determination, and a RSA test (2×6×35-m all-out sprints) Pre- and Post-HIIT. Before and after RSA, the neuromuscular function was assessed with counter movement jumps (CMJ) and knee extensors maximal isometric voluntary contractions (MVC) with femoral nerve electrical stimulation. Long-HIIT consisted of 10×1-min runs at 90% of V INC with 1-min recovery. Results: Long-HIIT induced significant increase in V̇O 2 max (P=0.0001). Although anaerobic capacity did not change significantly, 60% of the participants improved above the smallest worthwhile change (0.2×standard deviation of Pre-HIIT). The changes in sprint performance over RSA was significantly less post-HIIT than pre (P=0.01). RSA induced significant drop of MVC, high frequency doublet, voluntary activation and CMJ performance at Pre- and Post-HIIT (P<0.01), however, the percentage of reduction from rest to fatigued conditions were not significantly altered at Post-HIIT compared to Pre. Conclusion: 11 sessions of long-HIIT over 4-week improve maximal aerobic power but not anaerobic capacity, and neuromuscular function. Yet, neuromuscular fatigue was similar despite greater speeds reached during RSA. neuromuscular fatigue central fatigue peripheral fatigue sport performance repeated sprint ability Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction High-intensity interval training (HIIT) is characterized by intermittent efforts of vigorous exercise, interspersed by periods of rest or low intensity exercise ( 1 ). HIIT has been proposed as a time-efficient alternative to traditional continuous/endurance training, promoting similar adaptations in several cardiorespiratory, physiological, and health-related markers in healthy and diseased populations ( 1 – 3 ). Also, the acute and chronic physiological effects of HIIT programs are directly related to the precise manipulation of several variables (i.e., intensity, interval duration, relief duration, etc.) that compose the different HIIT set ups ( 3 ). Buchheit and Laursen ( 3 ) characterized the physiological strain/adaptations induced by each type of HIIT. Although the enhancement of cardiorespiratory system is often assumed as the primary objective of a HIIT program ( 1 , 3 ), short interval HIIT (short-HIIT - intervals < 1 min, intensity 100% – 120% maximal oxygen uptake [V̇O 2 max] and work:rest ratio = 1:1) and especially sprint interval training (SIT – intervals 10–30 s, intensity between 150% V̇O 2 max – all out and and work:rest ratio = 1:4–1:8) can substantially challenge/enhance the non-oxidative energy pathways (i.e., glycolytic and phosphagen pathways) (3,4) and neuromuscular system (5,6). The anaerobic and neuromuscular adaptations following long interval HIIT (long-HIIT - interval ≥ 1 min and intensity 85% − 100% V̇O 2 max), however, have been under investigated. Panissa et al. ( 7 ) measured the contribution of the anaerobic pathways during a long-HIIT session composed of 10 × 1-min runs at 100% of V̇O 2 max, interspaced by 1 min of passive recovery, and demonstrated that anaerobic contribution was 32 ± 5% of total energy expenditure when considering the exercise efforts plus recovery, and 46 ± 5% when considering only efforts, confirming a relevant contribution of anaerobic pathways to the total energy expenditure during a long-HIIT session. This may explain why Little et al. (2) showed an 11% improvement in an anaerobic cycling time-trial (time needed to reach 50 kJ, ~ 120 s at mean power of 436 ± 22 W) after only six sessions of long-HIIT (8–12 × 1-min cycling at 100% of peak power output with 75 s of recovery). Regarding neuromuscular adaptations induced by long-HIIT, data are even scarcer ( 8 ). Martinez-Valdes et al. ( 8 ) investigated the effect of long-HIIT (8–12 × 1-min at 100% of peak power output reached in an incremental test with 75 s of recovery) on neuromuscular function and showed a ~ 7% increase in knee extensors maximal torque after six sessions of long-HIIT. Electromyographic activity of vastus medialis , and vastus lateralis muscles also increased by ~ 17% and ~ 14%, respectively, suggesting neural adaptations. Based on the previously established anaerobic and neuromuscular demand of long-HIIT, this type of training could be considered as an interesting protocol to enhance the anaerobic system and neuromuscular function and must be investigated for a more comprehensive understand. Similarly, the ability to perform sprints repeatedly (RSA) with short recovery periods could also benefit, since RSA has a high energetic contribution from anaerobic pathways ( 9 , 10 ), and induces significant neuromuscular fatigue at the peripheral and central levels ( 11 , 12 ). Finally, the utilization of long-HIIT, as opposed to short-HIIT and SIT, may be a safer and more appealing strategy, especially for non-trained individuals (i.e., sedentary and physically active), who may not tolerate the extreme intensity of short-HIIT and SIT ( 1 ). Therefore, the aim of the present study was to investigate the effect of long-HIIT program on the anaerobic energy systems, RSA performance and neuromuscular function. Since the present investigation is the first to perform a comprehensive analysis of the capacity of a long-HIIT program to induce positive adaptations on the anaerobic system and neuromuscular function, we hypothesized that, besides aerobic gains, long-HIIT would enhance anaerobic capacity and attenuate the neuromuscular fatigue induced by RSA, consequently improving RSA performance. Methods Participants Twenty healthy men, physically active (age: 25 ± 5 years; height: 1.74 ± 0.07 m; weight: 73.5 ± 8.4 kg; V̇O 2 max: 44.8 ± 5.3 mL.kg −1 .min −1 ) participated in the study. Participants were free of any musculoskeletal disorders and were requested to abstain from strenuous activities and caffeine for 24-h and consume a light meal 2-h before each session. The study was approved by the Local Ethics Committee and was conducted according to the Declaration of Helsinki. All participants were informed about the procedures, benefits and risks of the investigation before signing an informed consent form prior to beginning the study. Experimental design The participants attended two familiarization sessions and were evaluated Pre- and Post-HIIT at the same time of the day (± 3 p.m.). Each evaluation consisted of three sessions carried out on separate days with 48 h recovery between them (Fig. 1 ). On day 1, the participants performed an incremental running test (T INC ) until task failure. A supramaximal running test (T SUPRA ) to the task failure and the RSA test were performed on days 2 and 3. Before (at rest) and after (fatigued state) RSA, neuromuscular assessments were performed consisting of three counter movement jumps (CMJ) and three maximal voluntary isometric contractions (MVC) with electrically evoked contractions. During the T INC and T SUPRA , oxygen uptake (V̇O 2 ) was measured breath-by-breath using an ergospirometer (Quark PFT, Cosmed, Rome, Italy) and heart rate was measured using a transmitter belt coupled to the gas analyzer (Wireless HR 138 monitor; Cosmed, Rome, Italy). The blood lactate concentration was analyzed in an electrochemical analyzer YSI 2300 STAT (Yellow Spring Instruments, Yellow Spring, OH). The physiological variables analyze are described in details in Milioni et al. (13). Approximately 72–96 h following the RSA test, the participants started the long-HIIT program, which lasted 4 weeks. The Post-HIIT evaluations were performed 72–96 h after the last training session (Fig. 1 ). Incremental running test (T INC ) After 5-min warm up at 8 km.h − 1 , participants performed the T INC on a stationary treadmill (ATL, Inbramed, Porto Alegre, Brazil), which started at 8 km.h − 1 with increments of 1.5 km.h − 1 every 2 min until task failure ( 13 ). The V̇O 2 max, maximal heart rate (HR max ), maximal velocity achieved in the T INC (V INC ) and peak blood lactate concentration ([La] peak ) were determined according Milioni et al. (13) procedures. Supramaximal running test (T SUPRA ) and anaerobic capacity (AC [La+PCr] ) determination The participants remained seated for 10 min to determine baseline V̇O 2 and blood lactate concentration. After the baseline measurements, the participants performed a warm-up at 8 km.h −1 for 5 min followed by a supramaximal running at 115% of V INC until the task failure (14,15). Determination of AC [La+PCr] was the primary aim of the T SUPRA ; since the intensity in which the test is carried out is protocol-dependent ( 14 , 15 ), the intensity of the T SUPRA carried out at Post-HIIT was properly adjusted according the Post-HIIT T INC performance. After the task failure, VO 2 measurements continued for ~ 10 min (until the VO 2 stabilization at 2–3 mL.kg −1 .min −1 above baseline) to determine the fast phase of the excess post oxygen consumption (EPOC fast ). Blood samples were collected 3, 5, and 7 min after the task failure for determination of the peak blood lactate concentration (14,15). The sum of the oxygen equivalents from the glycolytic ( E La ) and phosphagen ( E PCr ) energy systems was considered as a representative index of the anaerobic capacity (AC [La+PCr] )( 14 , 15 ) and were estimated according Zagatto et al.( 14 ) and Miyagy et al. ( 15 ). Repeated sprint ability test (RSA) After a 5 min warm-up at 8 km.h − 1 , the participants performed the Running-Based Anaerobic Sprint Test (RAST) twice ( 10 , 16 ), interspaced by 4-min of passive recovery. Briefly, the RAST consisted of six 35-m all-out efforts with 10-s passive recovery between sprints. The variables extracted from the RSA were total time (sum of 35-m sprint times), best time (best 35-m sprint time), performance decrement [100 × (total time / (best time × 12) – 100] and peak blood lactate concentration. The procedures of RSA data collection and analysis are fully described in Milioni et al. ( 13 ). Neuromuscular function assessments Pre- and Post-HIIT, neuromuscular function was assessed by CMJ and MVC with electrically-evoked contractions, at rest (before RSA) and at fatigued state (after RSA). Vertical jumps . A set of three CMJ (Jump test, CEFISE, Nova Odessa, SP, Brazil) with a 1-min rest between jumps was performed, and the highest jump attempt (cm) of each participant was measured ( 13 ). Force measurements and femoral nerve electrical stimulations . After the jumps, the participants performed three MVCs with a 1-min rest. The hips and knees were firmly fixed in a chair at 90° flexion with straps crossed on the chest, hip, and thigh. To measure the isometric force of the knee extension, the ankle of the dominant leg was attached to a load cell (SDK200, Miotec, Porto Alegre, RS, Brazil). The force signal was acquired at 2000 Hz. Supramaximal, square-wave, electrical pulses were delivered on the femoral nerve by a constant current electrical stimulator (Bioestimulador, Insigth, Ribeirão Preto, SP, Brazil) (400 V max). Electrodes with conductive gel (5 × 5 cm) were placed in the femoral triangle (cathode) and the gluteal fold (anode). The optimal intensity of stimulation was determined by the application of consecutive and incremental doublet pulses (100 Hz; Db100) to the relaxed muscle until reaching the twitch force plateau ( 17 ). Supramaximal stimulation was ensured by increasing the stimulation intensity by 20%. The following sequence of femoral nerve electrical stimulations was applied: Db100 superimposed to MVC (Db100 sup ) and potentiated Db100 on relaxed muscle 5 s after MVC termination (Fig. 1 ). The data analyses and variables extraction (MVC peak force, Db100 and voluntary activation [VA]) were carried out using specific MatLab algorithms (The Math Works Inc, Natick, MA), according to Milioni et al. ( 13 ). High Intensity interval training (HIIT) The long-HIIT program was derived from Little et al. ( 2 ). After a 5-min warm-up at 8 km.h − 1 , the HIIT sessions consisted of 10 × 1-min runs at 90% of V INC with 1-min of passive recovery. Participants were required to achieve at least 90% of HR max in the last 5 runs, and if this was not achieved, the intensity was increased by ~ 3% of V INC in the subsequent HIIT session. HR (Polar RS400, Kempele, Finland) was measured in each run. All training sessions were performed on a treadmill (ATL, Inbramed, Porto Alegre, RS, Brazil), and participants were required to attend 11 training sessions over 4 weeks, (3 sessions in the first 3 weeks and 2 sessions in the last week) with 36 h – 72 h rest between sessions. Statistical analysis All data are presented as mean ± standard deviation (SD) and effect size (i.e., Cohen’s d for t-test (ES) and partial eta square for ANOVA (η 2 )). Initially, the Shapiro-Wilk test was performed to confirm normality of the data. A paired student t-test was used to compare variables from the T INC , T SUPRA , and RSA (Pre- vs Post-HIIT). A two-way ANOVA with repeated measures was used to analyze sprint performance and neuromuscular function. The Sidak post hoc was applied when significant differences were demonstrated by the ANOVA analyses. The significance level was determined as 5% (P < 0.05). Additionally, the T SUPRA and RSA outcomes were qualitatively analyzed. The smallest worthwhile change (SWC) was calculated (Pre-HIIT SD multiplied by 0.2) ( 18 ) and the individual Pre- to Post-HIIT variation (Δ) of variables was plotted. The number of cases among the 20 participants in which the Δ were greater than the SWC were counted. Results HIIT All participants successfully completed the training intervention. The intensity of the first training session was 12.4 ± 1.5 km.h − 1 (90 ± 0.0% V INC ) while the final session was performed at 13.6 ± 1.7 km.h − 1 (99.0 ± 2.6% V INC ). The percentage of HR max reached in the last five runs (89 ± 2%) over the 4 weeks of training was not statistically different (F (1, 19) = 2.2; P = 0.06) between HIIT sessions. Incremental running test V̇O 2 max, V INC , and peak blood lactate concentration increased significantly after 4 weeks of HIIT, whereas HR max was not significantly different between Pre and Post-HIIT (Table 1 ). Supramaximal running test No significant differences were found between Pre and Post-HIIT for AC [La+PCr] , E La , E PCr and peak blood lactate concentration. Time-to-task failure during the T SUPRA was significantly decreased at Post-HIIT (Table 1 ). Table 1 Mean ± SD outcomes of incremental running test (T INC ) Pre-HIIT Post-HIIT % change ES P Incremental running test V̇O 2 max (mL.kg − 1 .min − 1 ) 44.8 ± 5.3 46.9 ± 4.9 4.9 ± 4.3 0.38 0.0001 V INC (km.h − 1 ) 13.7 ± 1.7 14.5 ± 1.4 5.9 ± 4.8 0.44 0.0001 [La] peak (mmol.L − 1 ) 10.7 ± 2.1 11.4 ± 1.4 9.2 ± 15.7 0.35 0.03 HR max (bpm) 191 ± 10 193 ± 9 0.8 ± 2.7 0.13 0.22 Supramaximal running test AC [La+PCr] (L.O 2 ) 3.70 ± 0.42 3.85 ± 0.69 4.0 ± 13.7 0.34 0.22 E La (L.O 2 ) 2.33 ± 0.29 2.40 ± 0.50 2.9 ± 18.7 0.21 0.53 E PCr (L.O 2 ) 1.37 ± 0.27 1.45 ± 0.38 8.1 ± 26.4 0.31 0.31 [La] peak (mmol.L − 1 ) 11.7 ± 1.7 11.9 ± 2.3 2.9 ± 17.3 0.15 0.58 TTF (s) 167 ± 34 144 ± 29 -11.6 ± 21.4 -0.63 0.01 V̇O 2 max : Maximal oxygen uptake; V INC : highest velocity achieved during T INC ; [La] peak : Peak of blood lactate concentration; HR max : Maximal heart rate; AC [La+PCr] : Anaerobic capacity; E La : Oxygen equivalents from the glycolytic energy systems; E PCr : Oxygen equivalents from the phosphagen energy systems; TTF : time-to-task failure during the T SUPRA Repeated sprint ability test The sprint times increased significantly throughout the RSA test (F (1, 19) = 79.4; P < 0.001; η 2 : 0.81). There was a significant sprint × time interaction (F (1, 19) = 7.2; P < 0.001; η 2 : 0.28), with slower velocity during sprint #2 at Post-HIIT compared to Pre-HIIT (P = 0.009), and faster velocities during #10, #11 and #12 sprints at Post-HIIT compared to Pre-HIIT (P < 0.043) (Fig. 2 ). There were no significant changes from Pre- to Post-HIIT for total time or best time. However, performance decrement and peak blood lactate were significantly decreased at Post-HIIT (Table 2 ). Table 2 Mean ± SD outcomes of repeated sprint ability test (RSA) Pre-HIIT Post-HIIT % change ES P Total time (s) 74.45 ± 5.03 73.98 ± 3.63 0.4 ± 4.8 -0.09 0.57 Best time (s) 5.30 ± 0.23 5.39 ± 0.23 1.9 ± 5.9 0.39 0.20 %Dec (%) 17.1 ± 6.3 14.5 ± 5.4 -12.3 ± 24.2 -0.39 0.01 [La] peak (mmol.L − 1 ) 15.2 ± 2.4 14.1 ± 1.8 9.2 ± 15.7 -0.43 0.04 %Dec : Performance decrement; [La] peak : Peak of blood lactate concentration Smallest worthwhile change of AC [La+PCr] and RSA variables Absolute Pre- to Post-HIIT change above the SWC for AC [La+PCr] , E La and E PCr was 60% (12 out of 20), 45% (9 out of 20) and 60% (12 out of 20) of the participants, whereas 35% of the participants (7 out of 20) improved the total time and 25% (5 out 20) improved the best time above the SWC (Fig. 3 ). Neuromuscular function assessments RSA induced a significant decrement in MVC (F (1, 19) = 32.7; P = 0.001; η 2 : 0.53), Db100 (F (1, 19) = 12.5; P = 0.01; η 2 : 0.32), VA (F (1, 19) = 11.7; P = 0.001; η 2 : 0.30) and CMJ performance (F (1, 19) = 112.3; P = 0.001; η 2 : 0.79), at Pre- and Post-HIIT. There was no significant RSA effect × time interaction for any variable (F (1, 19) 0.28; η 2 : < 0.14). The percentage of reduction induced by RSA for MVC (P = 0.44; ES: 0.13), Db100 (P = 0.93; ES: -0.02), VA (P = 0.98; ES: 0.01) and CMJ performance (P = 0.14; ES: 0.29) were not statistically different between Pre- and Post-HIIT (Fig. 4 ). Discussion The present study investigated the effects of 11 long-HIIT training sessions covered in four weeks on anaerobic capacity, neuromuscular function and RSA performance. In addition to the expected aerobic gains, the main findings were the non-significant changes in AC [La+PCr] or RSA performance. Although changes in AC [La+PCr] and E PCr presented a high rate of responsiveness (60% of the participants), that was not directly transfer into RSA total time and best time performance. Neuromuscular fatigue after four weeks of long-HIIT was similar despite greater speeds reached during RSA. Anaerobic Capacity adaptations after long-HIIT The ~ 5% improvement in V̇O 2 max as well as the significant increase in V INC, corroborate many previous studies indicating that long-HIIT is effective for inducing positive adaptations in the cardiorespiratory and oxidative systems ( 19 , 20 ), because it allows individuals to spend a long time in the so-called red zone, i.e., above 90% of V̇O 2 max (3,21). Lee et al. (22) and Campos et al. (23) reported RSA improvements along with an impressive V̇O 2 max enhancement after HIIT program (+ 18.4%; 51.9 ± 9.2 mL.kg −1 .min −1 to 61.4 ± 12.2 mL.kg −1 .min −1 and ~ + 6%; 56.5 ± 5.2 mL.kg −1 .min −1 to 59.9 ± 4.1 mL.kg −1 .min −1 , respectively), contrary to McGinley and Bishop (24) who did not show any alteration in V̇O 2 max ( ~ + 1.7%; 47.7 ± 5.5 mL.kg − 1 .min −1 to 48.5 ± 5.1 mL.kg − 1 .min −1 ). The enhancement of V̇O 2 max shown in the present study is more modest than Lee et al. (22), similar to Campos et al. (23), but higher than McGinley and Bishop (24) and may play an important role in performance maintenance during short sprints (≤ 10 s). Indeed, Milioni et al. (25) found a significant increase in the oxidative system contribution after the third sprint during 6 × 35-m all-out sprints with 10 s of passive recovery, as well as a significant association with total time, best time, worst time, and mean time. Reinforcing these findings, McGawley and Bishop (26) found strong correlations (r = 0.81–0.93, P < 0.01) between the oxidative contribution during the fifth, sixth, and tenth 6-s all-out We hypothesized that 4 weeks of long-HIIT would enhance AC [La+PCr] , however, that was not confirmed. The present study qualitatively analyzed results based on absolute variation between Pre- and Post-HIIT and the smallest worthwhile change (SWC), since sometimes “null hypothesis” statistics is not sensitive enough to detect small important changes induced by a training intervention ( 27 ). In the present study, 60% of the participants improved their AC [La+PCr] above the meaningful threshold of SWC, and among the twelve participants that increased the AC [La+PCr] , nine of them also increased their E PCr above the SWC. The 1-min passive recovery between bouts may allow significant replenishment of the muscle PCr storage ( 9 ), reloading this energy system for the subsequent effort, which may induce positive adaptations to the phosphagen system as suggested by Bishop et al. ( 28 ). In addition, the readiness of the phosphagen system and the 1-min work interval at submaximal intensity (i.e., 90% of V INC ) may demand less from the glycolytic system ( 5 ), not being enough to enhance this energy system. In fact, when longer work intervals are used (i.e., 4 min instead 1 min), significant increase in peak lactate concentration was verified ( 29 ). During supramaximal efforts (i.e.; 115% of V̇O 2 max intensity), the glycolytic contribution is close to 60% of the total anaerobic energy expenditure ( 14 , 15 ), therefore, this non-significant improvement in glycolytic system may explain the lack of AC [La+PCr] enhancement. Still, the key factor to improve anaerobic capacity might be the exercise intensity and, consequently, the high demand of the non-mitochondrial energy pathways, since Tabata et al. ( 30 ) and Ravier et al. ( 31 ) found significant improvement of maximal accumulated oxygen deficit (28% – 10.3%) after 2–4 training sessions per week during 6–7 weeks, composed of 6–9 bouts of 20-s of cycling/running at 140% – 170% of intensity attained at V̇O 2 max with 10–15 s of passive recovery. Repeated Sprint Ability after long-HIIT Total time and best time for the RSA were not modified following training and there was a low responsiveness of the participants (35% were above the SWC for total time and 25% for best time). The absence of an improvement in best time was expected and was likely related to the long-HIIT set up, since shorter intervals with higher intensity are closely linked to sprint speed development ( 3 , 5 ). In contrast, the performance in sprints #10, #11 and #12 were significantly faster at Post-HIIT compared with Pre-HIIT, which is in line with the improvement of performance decrement. This particular topic (i.e., RSA enhancement by long-HIIT) is not deeply investigated in literature, and the different long-HIIT set ups may be an important confounding factor and generate divergent results. For instance, after long-HIIT, Lee et al. ( 22 ) found significant improvements in peak power output, mean power output and performance decrement during 6 × 10-s all-out cycling sprints with 1-min active recovery at 50 W, Campos et al. ( 23 ) found improvement only in a mean time of a specific RSA test and McGinley and Bishop ( 24 ) did not find any significant change in total work and performance decrement during 5 × 6-s all-out cycling sprints with 24-s passive recovery. Neuromuscular function assessment As expected, all-out repeated sprints (i.e., RSA) induced both central and peripheral fatigue ( 12 , 13 , 32 ) at Pre- and Post-HIIT. Also, the long-HIIT program did not change neuromuscular function at rest or in a fatigued state, as well as did not alter neuromuscular fatigue resistance either, since the percentage of reduction induced by RSA at Pre- and Post-HIIT was not statistically different for any neuromuscular variable. Yet, the same neuromuscular fatigue was observed with more power produced during the sprints #10, #11 and #12. More intense HIIT set ups, especially SIT, have shown effective results in terms of neuromuscular function, inducing enhancement of muscle activation, maximal force, explosive force, and reducing the co-activation of agonist muscle ( 6 , 33 ). The higher intensities and shorter intervals induce more accelerations, decelerations and re-accelerations, generating higher neuromuscular loads ( 5 ), which may contribute to improve the tolerance to neuromuscular fatigue through an increment in the sensory threshold of group III/IV muscle afferent inhibitory nerves. Regarding the CMJ performance, which reflects muscle activation and muscle contractile properties ( 5 ), the present study presented a negligible + 0.1% improvement (at rest) after 11 sessions of long-HIIT. To the best of our knowledge, only two works have investigated the effect of long-HIIT on CMJ performance. Whereas Viaño-Santasmarinas et al.( 34 ) showed non-significant ~ + 1.6% increase after 12 sessions, Campos et al.( 23 ) found ~ + 8.6% after 8 sessions. Both studies( 23 , 34 ) were conducted with intermittent sports athletes (handball and futsal), who remain in their daily-based training routine, including strength training and technical-tactical sport-related sessions with jumps and change of direction, which may explain the discrepant results among three studies. Limitations The absence of a control group and/or a group performing another type of HIIT is a negative point in our investigation. Also, the fact that the subjects in the present study were not specifically trained may generate different results compared to the same intervention (i.e., 4-week long-HIIT) applied to highly trained subjects or sprint-trained subjects. Conclusion The findings of the present study provided a comprehensive overview of the effects of a short-term (4 weeks) long-HIIT program. It confirmed the significantly increases V̇O 2 max and, more importantly, adds new knowledge on the effects of this type of training. Despite no significant differences, 60% of the participants improved their anaerobic capacity above the meaningful threshold of SWC after this specific long-HIIT model. This outcome may be due the discrete enhancement in the phosphagen pathway contribution. The capacity to maintain RSA performance was also improved and the enhanced oxidative system may have played an important role in this outcome. The long-HIIT did not alter neuromuscular function at rest or in a fatigue state, or affect neuromuscular fatigue resistance. Most likely, the training intensity is the key factor to anerobic and neuromuscular adaptations, as induced by short-HIIT and SIT (3,5). Therefore, the present investigation is highly applicable in a practical context, since data regarding the anaerobic and neuromuscular adaptations induced by long-HIIT interventions are scarce and the present work provides evidence that may help athletes and coaches to accurately plan the adaptations promoted by a long-HIIT program. Future studies should (i) investigate the effects of different periods of training interventions (i.e., 2 to 8 weeks) and (ii) test different populations such as highly-trained athletes. Declarations Competing interests: All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript. Alessandro Moura Zagatto is currently Section Editor of Sport Sciences for Health. Acknowledgments: The authors wish to thank participants for their enthusiastic participation and Dr Bryan Saunders for English proofread. This study was funded by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP - protocol nº 2016/11076-6). FM, RABP, GMPB and ESM scholarships are supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP - protocols nº 2016/02683-6, 2016/17836-2, 2017/03660-2 and 2017/21724-8). Authors contribution: All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Fabio Milioni, Guillaume Y Millet, Rodrigo de Araújo Bonetti de Poli, Gabriel Motta Pinheiro Brisola, Elvis de Souza Malta, Paulo Eduardo Redkva, Fabio Augusto Barbieri and Alessandro Moura Zagatto. The first draft of the manuscript was written by Fabio Milioni, Guillaume Y Millet and Alessandro Moura Zagatto and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. References Gibala MJ, Little JP, MacDonald MJ, Hawley JA. Physiological adaptations to low-volume, high-intensity interval training in health and disease. J Physiol [Internet]. 2012;590(5):1077–84. Little JP, Safdar A, Wilkin GP, Tarnopolsky MA, Gibala MJ. A practical model of low-volume high-intensity interval training induces mitochondrial biogenesis in human skeletal muscle: potential mechanisms. 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Is oxygen uptake measurement enough to estimate energy expenditure during high-intensity intermittent exercise? Quantification of anaerobic contribution by different methods. Front Physiol. 2018;9(JUL):1–8. Martinez-Valdes E, Falla D, Negro F, Mayer F, Farina D. Differential motor unit changes after endurance or high-intensity interval training. Med Sci Sports Exerc. 2017;49(6):1126–36. Gaitanos GC, Williams C, Boobis LH, Brooks S. Human muscle metabolism during intermittent maximal exercise. J Appl Physiol. 1993;75(2):712–9. Milioni F, Zagatto AM, Barbieri RA, Andrade VL, Dos Santos JW, Gobatto CA, et al. Energy systems contribution in the running-based anaerobic sprint test. Int J Sports Med. 2017;38(3):226–32. Girard O, Bishop DJ, Racinais S. Neuromuscular adjustments of the quadriceps muscle after repeated cycling sprints. PLoS One. 2013;8(5):1–9. Tomazin K, Morin JB, Millet GY. Etiology of neuromuscular fatigue after repeated sprints depends on exercise modality. Int J Sports Physiol Perform. 2017;12(7):878–85. Milioni F, De Poli RAB, Saunders B, Gualano B, Da Rocha AL, Da Silva ASR, et al. Effect of β-alanine supplementation during high-intensity interval training on repeated sprint ability performance and neuromuscular fatigue. J Appl Physiol. 2019;127(6):1599–610. Zagatto AM, Bertuzzi R, Miyagi WE, Padulo J, Papoti M. MAOD determined in a single supramaximal test: A study on the reliability and effects of supramaximal intensities. Int J Sports Med. 2016;37(9):700–7. Miyagi WE, Poli RA de, Papoti M, Bertuzzi R, Zagatto AM. Anaerobic capacity estimated in a single supramaximal test in cycling: Validity and reliability analysis. Sci Rep. 2017;7:42485. Zagatto AM, Beck WR, Gobatto CA. Validity of the running anaerobic sprint test for assessing anerobic power and predicting short-distance performances. J Strength Cond Res. 2009;23(6):1820–927. Milioni F, Vieira LHP, Barbieri RA, Zagatto AM, Nordsborg NB, Barbieri FA, et al. Futsal match-related fatigue affects running performance and neuromuscular parameters but not finishing kick speed or accuracy. Front Physiol. 2016;7:1–10. Cohen J. Statistical power analysis for the behavioral sciences. Vol. 2nd, Statistical Power Analysis for the Behavioral Sciences. Hillsdale: MI:Lawrence Erlbaum; 1988. Perry CGR, Heigenhauser GJF, Bonen A, Spriet LL. High-intensity aerobic interval training increases fat and carbohydrate metabolic capacities in human skeletal muscle. Applied Physiology, Nutrition, and Metabolism. 2008;33(6):1112–23. Perry CGR, Talanian JL, Heigenhauser GJF, Spriet LL. The effects of training in hyperoxia vs. normoxia on skeletal muscle enzyme activities and exercise performance. J Appl Physiol. 2006;102(3):1022–7. Millet GP, Candau R, Fattori P, Bignet F, Varray A. Responses to different intermittent runs at velocity associated with. Canadian Journal of Applied Physiology. 2003;28(3):410–23. Lee CL, Hsu WC, Cheng CF. Physiological adaptations to sprint interval training with matched exercise volume. Med Sci Sports Exerc. 2017;49(1):86–95. Campos F de S, Borszcz FK, Flores LJF, Barazetti LK, Teixeira AS, Hartmann Nunes RF, et al. HIIT Models in Addition to Training Load and Heart Rate Variability Are Related With Physiological and Performance Adaptations After 10-Weeks of Training in Young Futsal Players. Front Psychol. 2021 Jan 22;12. McGinley C, Bishop DJ. Influence of training intensity on adaptations in acid/base transport proteins, muscle buffer capacity, and repeated-sprint ability in active men. J Appl Physiol. 2016;121(6):1290–305. Milioni F, Zagatto A, Barbieri R, Andrade V, Santos J, Gobatto C, et al. Energy systems contribution in the running-based anaerobic sprint test. Int J Sports Med. 2017;38(03):226–32. McGawley K, Bishop DJ. Oxygen uptake during repeated-sprint exercise. J Sci Med Sport. 2015;18(2):214–8. Buchheit M. The numbers will love you back in return — I promise. Int J Sports Physiol Perform. 2016;11(4):551–4. Bishop D, Edge J, Thomas C, Mercier J. Effects of high-intensity training on muscle lactate transporters and postexercise recovery of muscle lactate and hydrogen ions in women. AJP: Regulatory, Integrative and Comparative Physiology. 2008;295(6):R1991–8. Stöggl TL, Björklund G. High intensity interval training leads to greater improvements in acute heart rate recovery and anaerobic power as high volume low intensity training. Front Physiol. 2017;8(August):1–8. Tabata I, Nishimura K, Kouzaki M, Hirai Y, Ogita F, Miyachi M, et al. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and ??VO2max. Medicine & Science in Sports & Exercise. 1996;28(10):1327–30. Ravier G, Dugué B, Grappe F, Rouillon JD. Impressive anaerobic adaptations in elite karate athletes due to few intensive intermittent sessions added to regular karate training. Scand J Med Sci Sports. 2009;19(5):687–94. Milioni F, Azevedo RA, Zagatto AM, Millet GY. Time Course of Recovery after Cycling Repeated Sprints. Med Sci Sports Exerc. 2021 Feb 1;53(2):413–20. Kinnunen JV, Piitulainen H, Piirainen JM. Neuromuscular adaptations to short-term high-intensity interval training in female ice hockey players. J Strength Cond Res. 2017;1. Viaño-Santasmarinas J, Rey E, Carballeira S, Padrón-Cabo A. Effects of high-intensity interval training with different interval durations on physical performance in handball players. J Strength Cond Res. 2018;32(12):3389–97. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 08 Mar, 2024 Reviews received at journal 28 Feb, 2024 Reviewers agreed at journal 07 Feb, 2024 Reviewers invited by journal 07 Feb, 2024 Editor assigned by journal 27 Jan, 2024 Submission checks completed at journal 27 Jan, 2024 First submitted to journal 25 Jan, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-3897583","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":269603147,"identity":"81a478bc-9f94-411f-a939-ce5357e5e43f","order_by":0,"name":"Fabio Milioni","email":"","orcid":"","institution":"Centro Universitário Nossa Senhora do Patrocínio (CEUNSP)","correspondingAuthor":false,"prefix":"","firstName":"Fabio","middleName":"","lastName":"Milioni","suffix":""},{"id":269603148,"identity":"5e50489c-ba06-459c-a5d2-5dd770bfef56","order_by":1,"name":"Guillaume Millet","email":"","orcid":"","institution":"Univ Lyon, UJM Saint-Etienne, Laboratoire Interuniversitaire de Biologie de la Motricité","correspondingAuthor":false,"prefix":"","firstName":"Guillaume","middleName":"","lastName":"Millet","suffix":""},{"id":269603149,"identity":"29d4cfbf-f9d0-4d65-a65b-1783873ff9da","order_by":2,"name":"Rodrigo Araújo Bonetti de Poli","email":"","orcid":"","institution":"São Paulo State University (UNESP), Faculty of Sciences, Department of Physical Education, Laboratory of Physiology and Human Performance, Post Graduate Program in Human Movement Sciences","correspondingAuthor":false,"prefix":"","firstName":"Rodrigo","middleName":"Araújo Bonetti","lastName":"de Poli","suffix":""},{"id":269603150,"identity":"4da2f82d-36f9-483e-be7a-4774b3caeefb","order_by":3,"name":"Gabriel Motta Pinheiro Brisola","email":"","orcid":"","institution":"São Paulo State University (UNESP), Faculty of Sciences, Department of Physical Education, Laboratory of Physiology and Human Performance, Post Graduate Program in Human Movement Sciences","correspondingAuthor":false,"prefix":"","firstName":"Gabriel","middleName":"Motta Pinheiro","lastName":"Brisola","suffix":""},{"id":269603151,"identity":"dcb1586e-f619-471e-bf68-12da28d64607","order_by":4,"name":"Elvis de Souza Malta","email":"","orcid":"","institution":"São Paulo State University (UNESP), Faculty of Sciences, Department of Physical Education, Laboratory of Physiology and Human Performance, Post Graduate Program in Human Movement Sciences","correspondingAuthor":false,"prefix":"","firstName":"Elvis","middleName":"de Souza","lastName":"Malta","suffix":""},{"id":269603152,"identity":"89314286-8baf-4b77-8be6-718f16990562","order_by":5,"name":"Paulo Eduardo Redkva","email":"","orcid":"","institution":"São Paulo State University (UNESP), Faculty of Sciences, Department of Physical Education, Laboratory of Physiology and Human Performance, Post Graduate Program in Human Movement Sciences","correspondingAuthor":false,"prefix":"","firstName":"Paulo","middleName":"Eduardo","lastName":"Redkva","suffix":""},{"id":269603153,"identity":"cb004ca2-01d8-4232-939e-386d8381168b","order_by":6,"name":"Fabio Augusto Barbieri","email":"","orcid":"","institution":"São Paulo State University (UNESP), Faculty of Sciences, Department of Physical Education Human Movement Lab, Post Graduate Program in Human Movement Sciences","correspondingAuthor":false,"prefix":"","firstName":"Fabio","middleName":"Augusto","lastName":"Barbieri","suffix":""},{"id":269603154,"identity":"efb881e3-a956-42ef-a82a-c866eb458f16","order_by":7,"name":"Alessandro Moura Zagatto","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5klEQVRIiWNgGAWjYDADfgYGNhibDZ9CKEgwYJBsIFmLwQFitfD3H3784uePP3LGN5KfPfhQwSDPL3aA7XEFHi0SB46ZWfYkGBib3UgzN5xxhsFw5uwEdsMz+Kw52GBmwJNgkLjtRoKZNG8b0I23E9iAHsMN5A+zfzP8A9SyeUb6N+K0GBzjMX4MsmWDRA6Rthie4SljlkkzNpY486ZMcsYZCaBfEtsN8WmRO39888c3NnJy/O3p2yQ+VNjI80snH3uITwsQsEmAKYEEEAliMxLQwMDA/AFM8R8gpHAUjIJRMApGKgAAw7VJ2Pk6MwQAAAAASUVORK5CYII=","orcid":"","institution":"São Paulo State University (UNESP), Faculty of Sciences, Department of Physical Education, Laboratory of Physiology and Human Performance, Post Graduate Program in Human Movement Sciences","correspondingAuthor":true,"prefix":"","firstName":"Alessandro","middleName":"Moura","lastName":"Zagatto","suffix":""}],"badges":[],"createdAt":"2024-01-25 15:03:59","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3897583/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3897583/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":50441066,"identity":"26c3d4f4-6657-4f9d-a943-24cc71df342d","added_by":"auto","created_at":"2024-01-31 15:16:36","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":52080,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation of the experimental protocol. Numbers between brackets are recovery time. V\u003csub\u003eINC\u003c/sub\u003e: Maximal velocity achieved in incremental treadmill-running test; CMJ: Counter movement jump; MVC: Maximal isometric voluntary contractions of knee extension; NMA: Neuromuscular function assessment; T\u003csub\u003eINC\u003c/sub\u003e: Incremental treadmill-running test; T\u003csub\u003eSUPRA\u003c/sub\u003e: Supramaximal running test; RSA: Repeated sprint ability test\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-3897583/v1/19aeda4013cd43f061ffadbc.png"},{"id":50442979,"identity":"088d006e-e817-40b3-95f5-57eea849dc1d","added_by":"auto","created_at":"2024-01-31 15:24:36","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":62362,"visible":true,"origin":"","legend":"\u003cp\u003eMean (SD) of 12 × 35-m sprint time at Pre and Post-HIIT. \u003csup\u003e\u003cstrong\u003e#\u003c/strong\u003e\u003c/sup\u003eP \u0026lt; 0.05 comparison between Pre- and Post-HIIT of the same sprint\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-3897583/v1/712cfa35b507ad2644cead3e.png"},{"id":50441067,"identity":"c24d2fe4-57de-4f2c-b59e-e610cbccce7e","added_by":"auto","created_at":"2024-01-31 15:16:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":77962,"visible":true,"origin":"","legend":"\u003cp\u003eScatter dot plot of the qualitative analysis of long-HIIT effect on anaerobic capacity (top panel) and RSA performance (bottom panel) variables. Grey areas are the respective smallest worthwhile change (SWC). Bars are the group mean (SD)\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-3897583/v1/71d167c1172c176a28b835b4.png"},{"id":50441069,"identity":"0e14002c-b835-4fef-8674-2aa7d57b01b8","added_by":"auto","created_at":"2024-01-31 15:16:36","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":236292,"visible":true,"origin":"","legend":"\u003cp\u003eLeft panels: Mean ± SD outcomes of neuromuscular function assessment before (at rest) and after (fatigued state) RSA at Pre- and Post-HIIT. Right panels: Percentage of reduction induced by RSA at Pre- and Post-HIIT.\u003cstrong\u003e *\u003c/strong\u003eP \u0026lt; 0.05 comparison between Rest and Fatigue of the same time; \u003cstrong\u003e**\u003c/strong\u003eP \u0026lt; 0.01 comparison between Rest and Fatigue of the same time\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-3897583/v1/acb4cdc87fdd726744193e3b.png"},{"id":50444120,"identity":"824cb923-9249-4cfd-b852-9b5fdc81d6ea","added_by":"auto","created_at":"2024-01-31 15:32:37","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":938256,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3897583/v1/b999031b-a2d4-4dd6-94a3-671e191408a8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effects of 4-week high intensity interval training on anaerobic capacity, repeated-sprints performance and neuromuscular function","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHigh-intensity interval training (HIIT) is characterized by intermittent efforts of vigorous exercise, interspersed by periods of rest or low intensity exercise (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e). HIIT has been proposed as a time-efficient alternative to traditional continuous/endurance training, promoting similar adaptations in several cardiorespiratory, physiological, and health-related markers in healthy and diseased populations (\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e). Also, the acute and chronic physiological effects of HIIT programs are directly related to the precise manipulation of several variables (i.e., intensity, interval duration, relief duration, etc.) that compose the different HIIT set ups (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBuchheit and Laursen (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) characterized the physiological strain/adaptations induced by each type of HIIT. Although the enhancement of cardiorespiratory system is often assumed as the primary objective of a HIIT program (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e), short interval HIIT (short-HIIT - intervals\u0026thinsp;\u0026lt;\u0026thinsp;1 min, intensity 100% \u0026ndash; 120% maximal oxygen uptake [V̇O\u003csub\u003e2\u003c/sub\u003emax] and work:rest ratio\u0026thinsp;=\u0026thinsp;1:1) and especially sprint interval training (SIT \u0026ndash; intervals 10\u0026ndash;30 s, intensity between 150% V̇O\u003csub\u003e2\u003c/sub\u003emax \u0026ndash; all out and and work:rest ratio\u0026thinsp;=\u0026thinsp;1:4\u0026ndash;1:8) can substantially challenge/enhance the non-oxidative energy pathways (i.e., glycolytic and phosphagen pathways) (3,4) and neuromuscular system (5,6). The anaerobic and neuromuscular adaptations following long interval HIIT (long-HIIT - interval\u0026thinsp;\u0026ge;\u0026thinsp;1 min and intensity 85% \u0026minus;\u0026thinsp;100% V̇O\u003csub\u003e2\u003c/sub\u003emax), however, have been under investigated.\u003c/p\u003e \u003cp\u003ePanissa et al. (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e) measured the contribution of the anaerobic pathways during a long-HIIT session composed of 10 \u0026times; 1-min runs at 100% of V̇O\u003csub\u003e2\u003c/sub\u003emax, interspaced by 1 min of passive recovery, and demonstrated that anaerobic contribution was 32\u0026thinsp;\u0026plusmn;\u0026thinsp;5% of total energy expenditure when considering the exercise efforts plus recovery, and 46\u0026thinsp;\u0026plusmn;\u0026thinsp;5% when considering only efforts, confirming a relevant contribution of anaerobic pathways to the total energy expenditure during a long-HIIT session. This may explain why Little et al. (2) showed an 11% improvement in an anaerobic cycling time-trial (time needed to reach 50 kJ, ~\u0026thinsp;120 s at mean power of 436\u0026thinsp;\u0026plusmn;\u0026thinsp;22 W) after only six sessions of long-HIIT (8\u0026ndash;12 \u0026times; 1-min cycling at 100% of peak power output with 75 s of recovery).\u003c/p\u003e \u003cp\u003eRegarding neuromuscular adaptations induced by long-HIIT, data are even scarcer (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e). Martinez-Valdes et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e) investigated the effect of long-HIIT (8\u0026ndash;12 \u0026times; 1-min at 100% of peak power output reached in an incremental test with 75 s of recovery) on neuromuscular function and showed a\u0026thinsp;~\u0026thinsp;7% increase in knee extensors maximal torque after six sessions of long-HIIT. Electromyographic activity of \u003cem\u003evastus medialis\u003c/em\u003e, and \u003cem\u003evastus lateralis\u003c/em\u003e muscles also increased by ~\u0026thinsp;17% and ~\u0026thinsp;14%, respectively, suggesting neural adaptations.\u003c/p\u003e \u003cp\u003eBased on the previously established anaerobic and neuromuscular demand of long-HIIT, this type of training could be considered as an interesting protocol to enhance the anaerobic system and neuromuscular function and must be investigated for a more comprehensive understand. Similarly, the ability to perform sprints repeatedly (RSA) with short recovery periods could also benefit, since RSA has a high energetic contribution from anaerobic pathways (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e), and induces significant neuromuscular fatigue at the peripheral and central levels (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e). Finally, the utilization of long-HIIT, as opposed to short-HIIT and SIT, may be a safer and more appealing strategy, especially for non-trained individuals (i.e., sedentary and physically active), who may not tolerate the extreme intensity of short-HIIT and SIT (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTherefore, the aim of the present study was to investigate the effect of long-HIIT program on the anaerobic energy systems, RSA performance and neuromuscular function. Since the present investigation is the first to perform a comprehensive analysis of the capacity of a long-HIIT program to induce positive adaptations on the anaerobic system and neuromuscular function, we hypothesized that, besides aerobic gains, long-HIIT would enhance anaerobic capacity and attenuate the neuromuscular fatigue induced by RSA, consequently improving RSA performance.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eParticipants\u003c/h2\u003e \u003cp\u003eTwenty healthy men, physically active (age: 25\u0026thinsp;\u0026plusmn;\u0026thinsp;5 years; height: 1.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07 m; weight: 73.5\u0026thinsp;\u0026plusmn;\u0026thinsp;8.4 kg; V̇O\u003csub\u003e2\u003c/sub\u003emax: 44.8\u0026thinsp;\u0026plusmn;\u0026thinsp;5.3 mL.kg\u003csup\u003e\u0026minus;1\u003c/sup\u003e.min\u003csup\u003e\u0026minus;1\u003c/sup\u003e) participated in the study. Participants were free of any musculoskeletal disorders and were requested to abstain from strenuous activities and caffeine for 24-h and consume a light meal 2-h before each session. The study was approved by the Local Ethics Committee and was conducted according to the Declaration of Helsinki. All participants were informed about the procedures, benefits and risks of the investigation before signing an informed consent form prior to beginning the study.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eExperimental design\u003c/h2\u003e \u003cp\u003eThe participants attended two familiarization sessions and were evaluated Pre- and Post-HIIT at the same time of the day (\u0026plusmn;\u0026thinsp;3 p.m.). Each evaluation consisted of three sessions carried out on separate days with 48 h recovery between them (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). On day 1, the participants performed an incremental running test (T\u003csub\u003eINC\u003c/sub\u003e) until task failure. A supramaximal running test (T\u003csub\u003eSUPRA\u003c/sub\u003e) to the task failure and the RSA test were performed on days 2 and 3. Before (at rest) and after (fatigued state) RSA, neuromuscular assessments were performed consisting of three counter movement jumps (CMJ) and three maximal voluntary isometric contractions (MVC) with electrically evoked contractions. During the T\u003csub\u003eINC\u003c/sub\u003e and T\u003csub\u003eSUPRA\u003c/sub\u003e, oxygen uptake (V̇O\u003csub\u003e2\u003c/sub\u003e) was measured breath-by-breath using an ergospirometer (Quark PFT, Cosmed, Rome, Italy) and heart rate was measured using a transmitter belt coupled to the gas analyzer (Wireless HR 138 monitor; Cosmed, Rome, Italy). The blood lactate concentration was analyzed in an electrochemical analyzer YSI 2300 STAT (Yellow Spring Instruments, Yellow Spring, OH). The physiological variables analyze are described in details in Milioni et al. (13).\u003c/p\u003e \u003cp\u003eApproximately 72\u0026ndash;96 h following the RSA test, the participants started the long-HIIT program, which lasted 4 weeks. The Post-HIIT evaluations were performed 72\u0026ndash;96 h after the last training session (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eIncremental running test (T\u003csub\u003eINC\u003c/sub\u003e)\u003c/h2\u003e \u003cp\u003eAfter 5-min warm up at 8 km.h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, participants performed the T\u003csub\u003eINC\u003c/sub\u003e on a stationary treadmill (ATL, Inbramed, Porto Alegre, Brazil), which started at 8 km.h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with increments of 1.5 km.h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e every 2 min until task failure (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e). The V̇O\u003csub\u003e2\u003c/sub\u003emax, maximal heart rate (HR\u003csub\u003emax\u003c/sub\u003e), maximal velocity achieved in the T\u003csub\u003eINC\u003c/sub\u003e (V\u003csub\u003eINC\u003c/sub\u003e) and peak blood lactate concentration ([La]\u003csub\u003epeak\u003c/sub\u003e) were determined according Milioni et al. (13) procedures.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eSupramaximal running test (T\u003csub\u003eSUPRA\u003c/sub\u003e) and anaerobic capacity (AC\u003csub\u003e[La+PCr]\u003c/sub\u003e) determination\u003c/h2\u003e \u003cp\u003eThe participants remained seated for 10 min to determine baseline V̇O\u003csub\u003e2\u003c/sub\u003e and blood lactate concentration. After the baseline measurements, the participants performed a warm-up at 8 km.h\u003csup\u003e\u0026minus;1\u003c/sup\u003e for 5 min followed by a supramaximal running at 115% of V\u003csub\u003eINC\u003c/sub\u003e until the task failure (14,15). Determination of AC\u003csub\u003e[La+PCr]\u003c/sub\u003e was the primary aim of the T\u003csub\u003eSUPRA\u003c/sub\u003e; since the intensity in which the test is carried out is protocol-dependent (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e), the intensity of the T\u003csub\u003eSUPRA\u003c/sub\u003e carried out at Post-HIIT was properly adjusted according the Post-HIIT T\u003csub\u003eINC\u003c/sub\u003e performance. After the task failure, VO\u003csub\u003e2\u003c/sub\u003e measurements continued for ~\u0026thinsp;10 min (until the VO\u003csub\u003e2\u003c/sub\u003e stabilization at 2\u0026ndash;3 mL.kg\u003csup\u003e\u0026minus;1\u003c/sup\u003e.min\u003csup\u003e\u0026minus;1\u003c/sup\u003e above baseline) to determine the fast phase of the excess post oxygen consumption (EPOC\u003csub\u003efast\u003c/sub\u003e). Blood samples were collected 3, 5, and 7 min after the task failure for determination of the peak blood lactate concentration (14,15).\u003c/p\u003e \u003cp\u003eThe sum of the oxygen equivalents from the glycolytic (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eLa\u003c/sub\u003e) and phosphagen (\u003cem\u003eE\u003c/em\u003e\u003csub\u003ePCr\u003c/sub\u003e) energy systems was considered as a representative index of the anaerobic capacity (AC\u003csub\u003e[La+PCr]\u003c/sub\u003e)(\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e) and were estimated according Zagatto et al.(\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e) and Miyagy et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eRepeated sprint ability test (RSA)\u003c/h2\u003e \u003cp\u003eAfter a 5 min warm-up at 8 km.h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the participants performed the Running-Based Anaerobic Sprint Test (RAST) twice (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e), interspaced by 4-min of passive recovery. Briefly, the RAST consisted of six 35-m all-out efforts with 10-s passive recovery between sprints. The variables extracted from the RSA were total time (sum of 35-m sprint times), best time (best 35-m sprint time), performance decrement [100 \u0026times; (total time / (best time \u0026times; 12) \u0026ndash; 100] and peak blood lactate concentration. The procedures of RSA data collection and analysis are fully described in Milioni et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eNeuromuscular function assessments\u003c/h2\u003e \u003cp\u003ePre- and Post-HIIT, neuromuscular function was assessed by CMJ and MVC with electrically-evoked contractions, at rest (before RSA) and at fatigued state (after RSA).\u003c/p\u003e \u003cp\u003e \u003cem\u003eVertical jumps\u003c/em\u003e. A set of three CMJ (Jump test, CEFISE, Nova Odessa, SP, Brazil) with a 1-min rest between jumps was performed, and the highest jump attempt (cm) of each participant was measured (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cem\u003eForce measurements and femoral nerve electrical stimulations\u003c/em\u003e. After the jumps, the participants performed three MVCs with a 1-min rest. The hips and knees were firmly fixed in a chair at 90\u0026deg; flexion with straps crossed on the chest, hip, and thigh. To measure the isometric force of the knee extension, the ankle of the dominant leg was attached to a load cell (SDK200, Miotec, Porto Alegre, RS, Brazil). The force signal was acquired at 2000 Hz. Supramaximal, square-wave, electrical pulses were delivered on the femoral nerve by a constant current electrical stimulator (Bioestimulador, Insigth, Ribeir\u0026atilde;o Preto, SP, Brazil) (400 V max). Electrodes with conductive gel (5 \u0026times; 5 cm) were placed in the femoral triangle (cathode) and the gluteal fold (anode). The optimal intensity of stimulation was determined by the application of consecutive and incremental doublet pulses (100 Hz; Db100) to the relaxed muscle until reaching the twitch force plateau (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). Supramaximal stimulation was ensured by increasing the stimulation intensity by 20%. The following sequence of femoral nerve electrical stimulations was applied: Db100 superimposed to MVC (Db100\u003csub\u003esup\u003c/sub\u003e) and potentiated Db100 on relaxed muscle 5 s after MVC termination (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe data analyses and variables extraction (MVC peak force, Db100 and voluntary activation [VA]) were carried out using specific MatLab algorithms (The Math Works Inc, Natick, MA), according to Milioni et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eHigh Intensity interval training (HIIT)\u003c/h2\u003e \u003cp\u003eThe long-HIIT program was derived from Little et al. (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). After a 5-min warm-up at 8 km.h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the HIIT sessions consisted of 10 \u0026times; 1-min runs at 90% of V\u003csub\u003eINC\u003c/sub\u003e with 1-min of passive recovery. Participants were required to achieve at least 90% of HR\u003csub\u003emax\u003c/sub\u003e in the last 5 runs, and if this was not achieved, the intensity was increased by ~\u0026thinsp;3% of V\u003csub\u003eINC\u003c/sub\u003e in the subsequent HIIT session. HR (Polar RS400, Kempele, Finland) was measured in each run. All training sessions were performed on a treadmill (ATL, Inbramed, Porto Alegre, RS, Brazil), and participants were required to attend 11 training sessions over 4 weeks, (3 sessions in the first 3 weeks and 2 sessions in the last week) with 36 h \u0026ndash; 72 h rest between sessions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eAll data are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD) and effect size (i.e., Cohen\u0026rsquo;s d for t-test (ES) and partial eta square for ANOVA (η\u003csup\u003e2\u003c/sup\u003e)). Initially, the Shapiro-Wilk test was performed to confirm normality of the data. A paired student t-test was used to compare variables from the T\u003csub\u003eINC\u003c/sub\u003e, T\u003csub\u003eSUPRA\u003c/sub\u003e, and RSA (Pre- vs Post-HIIT).\u003c/p\u003e \u003cp\u003eA two-way ANOVA with repeated measures was used to analyze sprint performance and neuromuscular function. The Sidak \u003cem\u003epost hoc\u003c/em\u003e was applied when significant differences were demonstrated by the ANOVA analyses. The significance level was determined as 5% (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003eAdditionally, the T\u003csub\u003eSUPRA\u003c/sub\u003e and RSA outcomes were qualitatively analyzed. The smallest worthwhile change (SWC) was calculated (Pre-HIIT SD multiplied by 0.2) (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e) and the individual Pre- to Post-HIIT variation (Δ) of variables was plotted. The number of cases among the 20 participants in which the Δ were greater than the SWC were counted.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n\u003ch2\u003eHIIT\u003c/h2\u003e\n\u003cp\u003eAll participants successfully completed the training intervention. The intensity of the first training session was 12.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 km.h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0% V\u003csub\u003eINC\u003c/sub\u003e) while the final session was performed at 13.6\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7 km.h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (99.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6% V\u003csub\u003eINC\u003c/sub\u003e). The percentage of HR\u003csub\u003emax\u003c/sub\u003e reached in the last five runs (89\u0026thinsp;\u0026plusmn;\u0026thinsp;2%) over the 4 weeks of training was not statistically different (F\u003csub\u003e(1, 19)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;2.2; P\u0026thinsp;=\u0026thinsp;0.06) between HIIT sessions.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n\u003ch2\u003eIncremental running test\u003c/h2\u003e\n\u003cp\u003eV̇O\u003csub\u003e2\u003c/sub\u003emax, V\u003csub\u003eINC\u003c/sub\u003e, and peak blood lactate concentration increased significantly after 4 weeks of HIIT, whereas HR\u003csub\u003emax\u003c/sub\u003e was not significantly different between Pre and Post-HIIT (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n\u003ch2\u003eSupramaximal running test\u003c/h2\u003e\n\u003cp\u003eNo significant differences were found between Pre and Post-HIIT for AC\u003csub\u003e[La+PCr]\u003c/sub\u003e, \u003cem\u003eE\u003c/em\u003e\u003csub\u003eLa\u003c/sub\u003e, \u003cem\u003eE\u003c/em\u003e\u003csub\u003ePCr\u003c/sub\u003e and peak blood lactate concentration. Time-to-task failure during the T\u003csub\u003eSUPRA\u003c/sub\u003e was significantly decreased at Post-HIIT (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD outcomes of incremental running test (T\u003csub\u003eINC\u003c/sub\u003e)\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ePre-HIIT\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ePost-HIIT\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e% change\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eES\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eP\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eIncremental running test\u003c/em\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eV̇O\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003emax\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(mL.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e44.8\u0026thinsp;\u0026plusmn;\u0026thinsp;5.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e46.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.38\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.0001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eV\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eINC\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(km.h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e13.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e14.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.44\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.0001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e[La]\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003epeak\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(mmol.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10.7\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e11.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9.2\u0026thinsp;\u0026plusmn;\u0026thinsp;15.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.35\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.03\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eHR\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003emax\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(bpm)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e191\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e193\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.22\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eSupramaximal running test\u003c/strong\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eAC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e[La+PCr]\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(L.O\u003csub\u003e2\u003c/sub\u003e)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.69\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4.0\u0026thinsp;\u0026plusmn;\u0026thinsp;13.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.34\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.22\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eE\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eLa\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(L.O\u003csub\u003e2\u003c/sub\u003e)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.50\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;18.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.21\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.53\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eE\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ePCr\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(L.O\u003csub\u003e2\u003c/sub\u003e)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.37\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8.1\u0026thinsp;\u0026plusmn;\u0026thinsp;26.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.31\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.31\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e[La]\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003epeak\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(mmol.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e11.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e11.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;17.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.58\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eTTF\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(s)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e167\u0026thinsp;\u0026plusmn;\u0026thinsp;34\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e144\u0026thinsp;\u0026plusmn;\u0026thinsp;29\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-11.6\u0026thinsp;\u0026plusmn;\u0026thinsp;21.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-0.63\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.01\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003ctfoot\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"6\"\u003e\u003cstrong\u003eV̇O\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003emax\u003c/strong\u003e: Maximal oxygen uptake; \u003cstrong\u003eV\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eINC\u003c/strong\u003e\u003c/sub\u003e: highest velocity achieved during T\u003csub\u003eINC\u003c/sub\u003e; \u003cstrong\u003e[La]\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003epeak\u003c/strong\u003e\u003c/sub\u003e: Peak of blood lactate concentration; \u003cstrong\u003eHR\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003emax\u003c/strong\u003e\u003c/sub\u003e: Maximal heart rate; \u003cstrong\u003eAC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e[La+PCr]\u003c/strong\u003e\u003c/sub\u003e: Anaerobic capacity; \u003cstrong\u003eE\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eLa\u003c/strong\u003e\u003c/sub\u003e: Oxygen equivalents from the glycolytic energy systems; \u003cstrong\u003eE\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ePCr\u003c/strong\u003e\u003c/sub\u003e: Oxygen equivalents from the phosphagen energy systems; \u003cstrong\u003eTTF\u003c/strong\u003e: time-to-task failure during the T\u003csub\u003eSUPRA\u003c/sub\u003e\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tfoot\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n\u003ch2\u003eRepeated sprint ability test\u003c/h2\u003e\n\u003cp\u003eThe sprint times increased significantly throughout the RSA test (F\u003csub\u003e(1, 19)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;79.4; P\u0026thinsp;\u0026lt;\u0026thinsp;0.001; \u0026eta;\u003csup\u003e2\u003c/sup\u003e: 0.81). There was a significant sprint \u0026times; time interaction (F\u003csub\u003e(1, 19)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;7.2; P\u0026thinsp;\u0026lt;\u0026thinsp;0.001; \u0026eta;\u003csup\u003e2\u003c/sup\u003e: 0.28), with slower velocity during sprint #2 at Post-HIIT compared to Pre-HIIT (P\u0026thinsp;=\u0026thinsp;0.009), and faster velocities during #10, #11 and #12 sprints at Post-HIIT compared to Pre-HIIT (P\u0026thinsp;\u0026lt;\u0026thinsp;0.043) (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). There were no significant changes from Pre- to Post-HIIT for total time or best time. However, performance decrement and peak blood lactate were significantly decreased at Post-HIIT (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD outcomes of repeated sprint ability test (RSA)\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ePre-HIIT\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ePost-HIIT\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e% change\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eES\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eP\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eTotal time\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(s)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e74.45\u0026thinsp;\u0026plusmn;\u0026thinsp;5.03\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e73.98\u0026thinsp;\u0026plusmn;\u0026thinsp;3.63\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e0.4\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e-0.09\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.57\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003eBest time\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(s)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e5.30\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e5.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e1.9\u0026thinsp;\u0026plusmn;\u0026thinsp;5.9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.39\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.20\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e%Dec\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(%)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e17.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e14.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e-12.3\u0026thinsp;\u0026plusmn;\u0026thinsp;24.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e-0.39\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.01\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cstrong\u003e[La]\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003epeak\u003c/strong\u003e\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e(mmol.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e15.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e14.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e9.2\u0026thinsp;\u0026plusmn;\u0026thinsp;15.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e-0.43\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.04\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003ctfoot\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"6\"\u003e\u003cstrong\u003e%Dec\u003c/strong\u003e: Performance decrement; \u003cstrong\u003e[La]\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003epeak\u003c/strong\u003e\u003c/sub\u003e: Peak of blood lactate concentration\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tfoot\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n\u003ch2\u003eSmallest worthwhile change of AC\u003csub\u003e[La+PCr]\u003c/sub\u003e and RSA variables\u003c/h2\u003e\n\u003cp\u003eAbsolute Pre- to Post-HIIT change above the SWC for AC\u003csub\u003e[La+PCr]\u003c/sub\u003e, \u003cem\u003eE\u003c/em\u003e\u003csub\u003eLa\u003c/sub\u003e and \u003cem\u003eE\u003c/em\u003e\u003csub\u003ePCr\u003c/sub\u003e was 60% (12 out of 20), 45% (9 out of 20) and 60% (12 out of 20) of the participants, whereas 35% of the participants (7 out of 20) improved the total time and 25% (5 out 20) improved the best time above the SWC (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n\u003ch2\u003eNeuromuscular function assessments\u003c/h2\u003e\n\u003cp\u003eRSA induced a significant decrement in MVC (F\u003csub\u003e(1, 19)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;32.7; P\u0026thinsp;=\u0026thinsp;0.001; \u0026eta;\u003csup\u003e2\u003c/sup\u003e: 0.53), Db100 (F\u003csub\u003e(1, 19)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;12.5; P\u0026thinsp;=\u0026thinsp;0.01; \u0026eta;\u003csup\u003e2\u003c/sup\u003e: 0.32), VA (F\u003csub\u003e(1, 19)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;11.7; P\u0026thinsp;=\u0026thinsp;0.001; \u0026eta;\u003csup\u003e2\u003c/sup\u003e: 0.30) and CMJ performance (F\u003csub\u003e(1, 19)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;112.3; P\u0026thinsp;=\u0026thinsp;0.001; \u0026eta;\u003csup\u003e2\u003c/sup\u003e: 0.79), at Pre- and Post-HIIT. There was no significant RSA effect \u0026times; time interaction for any variable (F\u003csub\u003e(1, 19)\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;1.2; P\u0026thinsp;\u0026gt;\u0026thinsp;0.28; \u0026eta;\u003csup\u003e2\u003c/sup\u003e: \u0026lt; 0.14). The percentage of reduction induced by RSA for MVC (P\u0026thinsp;=\u0026thinsp;0.44; ES: 0.13), Db100 (P\u0026thinsp;=\u0026thinsp;0.93; ES: -0.02), VA (P\u0026thinsp;=\u0026thinsp;0.98; ES: 0.01) and CMJ performance (P\u0026thinsp;=\u0026thinsp;0.14; ES: 0.29) were not statistically different between Pre- and Post-HIIT (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe present study investigated the effects of 11 long-HIIT training sessions covered in four weeks on anaerobic capacity, neuromuscular function and RSA performance. In addition to the expected aerobic gains, the main findings were the non-significant changes in AC\u003csub\u003e[La+PCr]\u003c/sub\u003e or RSA performance. Although changes in AC\u003csub\u003e[La+PCr]\u003c/sub\u003e and \u003cem\u003eE\u003c/em\u003e\u003csub\u003ePCr\u003c/sub\u003e presented a high rate of responsiveness (60% of the participants), that was not directly transfer into RSA total time and best time performance. Neuromuscular fatigue after four weeks of long-HIIT was similar despite greater speeds reached during RSA.\u003c/p\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eAnaerobic Capacity adaptations after long-HIIT\u003c/h2\u003e \u003cp\u003eThe ~\u0026thinsp;5% improvement in V̇O\u003csub\u003e2\u003c/sub\u003emax as well as the significant increase in V\u003csub\u003eINC,\u003c/sub\u003e corroborate many previous studies indicating that long-HIIT is effective for inducing positive adaptations in the cardiorespiratory and oxidative systems (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e), because it allows individuals to spend a long time in the so-called red zone, i.e., above 90% of V̇O\u003csub\u003e2\u003c/sub\u003emax (3,21). Lee et al. (22) and Campos et al. (23) reported RSA improvements along with an impressive V̇O\u003csub\u003e2\u003c/sub\u003emax enhancement after HIIT program (+\u0026thinsp;18.4%; 51.9\u0026thinsp;\u0026plusmn;\u0026thinsp;9.2 mL.kg\u003csup\u003e\u0026minus;1\u003c/sup\u003e.min\u003csup\u003e\u0026minus;1\u003c/sup\u003e to 61.4\u0026thinsp;\u0026plusmn;\u0026thinsp;12.2 mL.kg\u003csup\u003e\u0026minus;1\u003c/sup\u003e.min\u003csup\u003e\u0026minus;1\u003c/sup\u003e and ~\u0026thinsp;+\u0026thinsp;6%; 56.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.2 mL.kg\u003csup\u003e\u0026minus;1\u003c/sup\u003e.min\u003csup\u003e\u0026minus;1\u003c/sup\u003e to 59.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1 mL.kg\u003csup\u003e\u0026minus;1\u003c/sup\u003e.min\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively), contrary to McGinley and Bishop (24) who did not show any alteration in V̇O\u003csub\u003e2\u003c/sub\u003emax (\u0026thinsp;~\u0026thinsp;+\u0026thinsp;1.7%; 47.7\u0026thinsp;\u0026plusmn;\u0026thinsp;5.5 mL.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.min\u003csup\u003e\u0026minus;1\u003c/sup\u003e to 48.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.1 mL.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.min\u003csup\u003e\u0026minus;1\u003c/sup\u003e). The enhancement of V̇O\u003csub\u003e2\u003c/sub\u003emax shown in the present study is more modest than Lee et al. (22), similar to Campos et al. (23), but higher than McGinley and Bishop (24) and may play an important role in performance maintenance during short sprints (\u0026le;\u0026thinsp;10 s). Indeed, Milioni et al. (25) found a significant increase in the oxidative system contribution after the third sprint during 6 \u0026times; 35-m all-out sprints with 10 s of passive recovery, as well as a significant association with total time, best time, worst time, and mean time. Reinforcing these findings, McGawley and Bishop (26) found strong correlations (r\u0026thinsp;=\u0026thinsp;0.81\u0026ndash;0.93, P\u0026thinsp;\u0026lt;\u0026thinsp;0.01) between the oxidative contribution during the fifth, sixth, and tenth 6-s all-out\u003c/p\u003e \u003cp\u003eWe hypothesized that 4 weeks of long-HIIT would enhance AC\u003csub\u003e[La+PCr]\u003c/sub\u003e, however, that was not confirmed. The present study qualitatively analyzed results based on absolute variation between Pre- and Post-HIIT and the smallest worthwhile change (SWC), since sometimes \u0026ldquo;null hypothesis\u0026rdquo; statistics is not sensitive enough to detect small important changes induced by a training intervention (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e). In the present study, 60% of the participants improved their AC\u003csub\u003e[La+PCr]\u003c/sub\u003e above the meaningful threshold of SWC, and among the twelve participants that increased the AC\u003csub\u003e[La+PCr]\u003c/sub\u003e, nine of them also increased their \u003cem\u003eE\u003c/em\u003e\u003csub\u003ePCr\u003c/sub\u003e above the SWC.\u003c/p\u003e \u003cp\u003eThe 1-min passive recovery between bouts may allow significant replenishment of the muscle PCr storage (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e), reloading this energy system for the subsequent effort, which may induce positive adaptations to the phosphagen system as suggested by Bishop et al. (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e). In addition, the readiness of the phosphagen system and the 1-min work interval at submaximal intensity (i.e., 90% of V\u003csub\u003eINC\u003c/sub\u003e) may demand less from the glycolytic system (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e), not being enough to enhance this energy system. In fact, when longer work intervals are used (i.e., 4 min instead 1 min), significant increase in peak lactate concentration was verified (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e). During supramaximal efforts (i.e.; 115% of V̇O\u003csub\u003e2\u003c/sub\u003emax intensity), the glycolytic contribution is close to 60% of the total anaerobic energy expenditure (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e), therefore, this non-significant improvement in glycolytic system may explain the lack of AC\u003csub\u003e[La+PCr]\u003c/sub\u003e enhancement.\u003c/p\u003e \u003cp\u003eStill, the key factor to improve anaerobic capacity might be the exercise intensity and, consequently, the high demand of the non-mitochondrial energy pathways, since Tabata et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e) and Ravier et al. (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e) found significant improvement of maximal accumulated oxygen deficit (28% \u0026ndash; 10.3%) after 2\u0026ndash;4 training sessions per week during 6\u0026ndash;7 weeks, composed of 6\u0026ndash;9 bouts of 20-s of cycling/running at 140% \u0026ndash; 170% of intensity attained at V̇O\u003csub\u003e2\u003c/sub\u003emax with 10\u0026ndash;15 s of passive recovery.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eRepeated Sprint Ability after long-HIIT\u003c/h2\u003e \u003cp\u003eTotal time and best time for the RSA were not modified following training and there was a low responsiveness of the participants (35% were above the SWC for total time and 25% for best time). The absence of an improvement in best time was expected and was likely related to the long-HIIT set up, since shorter intervals with higher intensity are closely linked to sprint speed development (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). In contrast, the performance in sprints #10, #11 and #12 were significantly faster at Post-HIIT compared with Pre-HIIT, which is in line with the improvement of performance decrement.\u003c/p\u003e \u003cp\u003eThis particular topic (i.e., RSA enhancement by long-HIIT) is not deeply investigated in literature, and the different long-HIIT set ups may be an important confounding factor and generate divergent results. For instance, after long-HIIT, Lee et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e) found significant improvements in peak power output, mean power output and performance decrement during 6 \u0026times; 10-s all-out cycling sprints with 1-min active recovery at 50 W, Campos et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e) found improvement only in a mean time of a specific RSA test and McGinley and Bishop (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e) did not find any significant change in total work and performance decrement during 5 \u0026times; 6-s all-out cycling sprints with 24-s passive recovery.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eNeuromuscular function assessment\u003c/h2\u003e \u003cp\u003eAs expected, all-out repeated sprints (i.e., RSA) induced both central and peripheral fatigue (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e) at Pre- and Post-HIIT. Also, the long-HIIT program did not change neuromuscular function at rest or in a fatigued state, as well as did not alter neuromuscular fatigue resistance either, since the percentage of reduction induced by RSA at Pre- and Post-HIIT was not statistically different for any neuromuscular variable. Yet, the same neuromuscular fatigue was observed with more power produced during the sprints #10, #11 and #12.\u003c/p\u003e \u003cp\u003eMore intense HIIT set ups, especially SIT, have shown effective results in terms of neuromuscular function, inducing enhancement of muscle activation, maximal force, explosive force, and reducing the co-activation of agonist muscle (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e). The higher intensities and shorter intervals induce more accelerations, decelerations and re-accelerations, generating higher neuromuscular loads (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e), which may contribute to improve the tolerance to neuromuscular fatigue through an increment in the sensory threshold of group III/IV muscle afferent inhibitory nerves.\u003c/p\u003e \u003cp\u003eRegarding the CMJ performance, which reflects muscle activation and muscle contractile properties (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e), the present study presented a negligible\u0026thinsp;+\u0026thinsp;0.1% improvement (at rest) after 11 sessions of long-HIIT. To the best of our knowledge, only two works have investigated the effect of long-HIIT on CMJ performance. Whereas Via\u0026ntilde;o-Santasmarinas et al.(\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e) showed non-significant\u0026thinsp;~\u0026thinsp;+\u0026thinsp;1.6% increase after 12 sessions, Campos et al.(\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e) found\u0026thinsp;~\u0026thinsp;+\u0026thinsp;8.6% after 8 sessions. Both studies(\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e) were conducted with intermittent sports athletes (handball and futsal), who remain in their daily-based training routine, including strength training and technical-tactical sport-related sessions with jumps and change of direction, which may explain the discrepant results among three studies.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eLimitations\u003c/h2\u003e \u003cp\u003eThe absence of a control group and/or a group performing another type of HIIT is a negative point in our investigation. Also, the fact that the subjects in the present study were not specifically trained may generate different results compared to the same intervention (i.e., 4-week long-HIIT) applied to highly trained subjects or sprint-trained subjects.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe findings of the present study provided a comprehensive overview of the effects of a short-term (4 weeks) long-HIIT program. It confirmed the significantly increases V̇O\u003csub\u003e2\u003c/sub\u003emax and, more importantly, adds new knowledge on the effects of this type of training. Despite no significant differences, 60% of the participants improved their anaerobic capacity above the meaningful threshold of SWC after this specific long-HIIT model. This outcome may be due the discrete enhancement in the phosphagen pathway contribution. The capacity to maintain RSA performance was also improved and the enhanced oxidative system may have played an important role in this outcome. The long-HIIT did not alter neuromuscular function at rest or in a fatigue state, or affect neuromuscular fatigue resistance. Most likely, the training intensity is the key factor to anerobic and neuromuscular adaptations, as induced by short-HIIT and SIT (3,5). Therefore, the present investigation is highly applicable in a practical context, since data regarding the anaerobic and neuromuscular adaptations induced by long-HIIT interventions are scarce and the present work provides evidence that may help athletes and coaches to accurately plan the adaptations promoted by a long-HIIT program. Future studies should (i) investigate the effects of different periods of training interventions (i.e., 2 to 8 weeks) and (ii) test different populations such as highly-trained athletes.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCompeting interests:\u0026nbsp;\u003c/strong\u003eAll authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript. Alessandro Moura Zagatto is currently Section Editor of Sport Sciences for Health.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u0026nbsp;\u003c/strong\u003eThe authors wish to thank participants for their enthusiastic participation and Dr Bryan Saunders for English proofread. This study was funded by Funda\u0026ccedil;\u0026atilde;o de Amparo \u0026agrave; Pesquisa do Estado de S\u0026atilde;o Paulo (FAPESP - protocol n\u0026ordm; 2016/11076-6). FM, RABP, GMPB and ESM scholarships are supported by Funda\u0026ccedil;\u0026atilde;o de Amparo \u0026agrave; Pesquisa do Estado de S\u0026atilde;o Paulo (FAPESP - protocols n\u0026ordm; 2016/02683-6, 2016/17836-2, 2017/03660-2 and 2017/21724-8).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors contribution:\u0026nbsp;\u003c/strong\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Fabio Milioni, Guillaume Y Millet, Rodrigo de Ara\u0026uacute;jo Bonetti de Poli, Gabriel Motta Pinheiro Brisola, Elvis de Souza Malta, Paulo Eduardo Redkva, Fabio Augusto Barbieri and Alessandro Moura Zagatto. The first draft of the manuscript was written by Fabio Milioni, Guillaume Y Millet and Alessandro Moura Zagatto and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eGibala MJ, Little JP, MacDonald MJ, Hawley JA. Physiological adaptations to low-volume, high-intensity interval training in health and disease. J Physiol [Internet]. 2012;590(5):1077\u0026ndash;84. \u003c/li\u003e\n\u003cli\u003eLittle JP, Safdar A, Wilkin GP, Tarnopolsky MA, Gibala MJ. A practical model of low-volume high-intensity interval training induces mitochondrial biogenesis in human skeletal muscle: potential mechanisms. J Physiol. 2010;588(6):1011\u0026ndash;22. \u003c/li\u003e\n\u003cli\u003eBuchheit M, Laursen PB. High-intensity interval training, solutions to the programming puzzle: Part I: Cardiopulmonary emphasis. Sports Medicine. 2013;43(5):313\u0026ndash;38. \u003c/li\u003e\n\u003cli\u003eBuckley S, Knapp K, Lackie A, Lewry C, Horvey K, Benko C, et al. Multimodal high-intensity interval training increases muscle function and metabolic performance in females. Applied Physiology, Nutrition, and Metabolism. 2015;40(11):1157\u0026ndash;62. \u003c/li\u003e\n\u003cli\u003eBuchheit M, Laursen PB. High-intensity interval training, solutions to the programming puzzle: Part II: Anaerobic energy, neuromuscular load and practical applications. Sports Medicine. 2013;43(10):927\u0026ndash;54. \u003c/li\u003e\n\u003cli\u003eCreer AR, Ricard MD, Conlee RK, Hoyt GL, Parcell AC. Neural, metabolic, and performance adaptations to four weeks of high intensity sprint-interval training in trained cyclists. Int J Sports Med. 2004;25(2):92\u0026ndash;8. \u003c/li\u003e\n\u003cli\u003ePanissa VLG, Fukuda DH, Caldeira RS, Gerosa-Neto J, Lira FS, Zagatto AM, et al. Is oxygen uptake measurement enough to estimate energy expenditure during high-intensity intermittent exercise? Quantification of anaerobic contribution by different methods. Front Physiol. 2018;9(JUL):1\u0026ndash;8. \u003c/li\u003e\n\u003cli\u003eMartinez-Valdes E, Falla D, Negro F, Mayer F, Farina D. Differential motor unit changes after endurance or high-intensity interval training. Med Sci Sports Exerc. 2017;49(6):1126\u0026ndash;36. \u003c/li\u003e\n\u003cli\u003eGaitanos GC, Williams C, Boobis LH, Brooks S. Human muscle metabolism during intermittent maximal exercise. J Appl Physiol. 1993;75(2):712\u0026ndash;9. \u003c/li\u003e\n\u003cli\u003eMilioni F, Zagatto AM, Barbieri RA, Andrade VL, Dos Santos JW, Gobatto CA, et al. Energy systems contribution in the running-based anaerobic sprint test. Int J Sports Med. 2017;38(3):226\u0026ndash;32. \u003c/li\u003e\n\u003cli\u003eGirard O, Bishop DJ, Racinais S. Neuromuscular adjustments of the quadriceps muscle after repeated cycling sprints. PLoS One. 2013;8(5):1\u0026ndash;9. \u003c/li\u003e\n\u003cli\u003eTomazin K, Morin JB, Millet GY. Etiology of neuromuscular fatigue after repeated sprints depends on exercise modality. Int J Sports Physiol Perform. 2017;12(7):878\u0026ndash;85. \u003c/li\u003e\n\u003cli\u003eMilioni F, De Poli RAB, Saunders B, Gualano B, Da Rocha AL, Da Silva ASR, et al. Effect of \u0026beta;-alanine supplementation during high-intensity interval training on repeated sprint ability performance and neuromuscular fatigue. J Appl Physiol. 2019;127(6):1599\u0026ndash;610. \u003c/li\u003e\n\u003cli\u003eZagatto AM, Bertuzzi R, Miyagi WE, Padulo J, Papoti M. MAOD determined in a single supramaximal test: A study on the reliability and effects of supramaximal intensities. Int J Sports Med. 2016;37(9):700\u0026ndash;7. \u003c/li\u003e\n\u003cli\u003eMiyagi WE, Poli RA de, Papoti M, Bertuzzi R, Zagatto AM. Anaerobic capacity estimated in a single supramaximal test in cycling: Validity and reliability analysis. Sci Rep. 2017;7:42485. \u003c/li\u003e\n\u003cli\u003eZagatto AM, Beck WR, Gobatto CA. Validity of the running anaerobic sprint test for assessing anerobic power and predicting short-distance performances. J Strength Cond Res. 2009;23(6):1820\u0026ndash;927. \u003c/li\u003e\n\u003cli\u003eMilioni F, Vieira LHP, Barbieri RA, Zagatto AM, Nordsborg NB, Barbieri FA, et al. Futsal match-related fatigue affects running performance and neuromuscular parameters but not finishing kick speed or accuracy. Front Physiol. 2016;7:1\u0026ndash;10. \u003c/li\u003e\n\u003cli\u003eCohen J. Statistical power analysis for the behavioral sciences. Vol. 2nd, Statistical Power Analysis for the Behavioral Sciences. Hillsdale: MI:Lawrence Erlbaum; 1988. \u003c/li\u003e\n\u003cli\u003ePerry CGR, Heigenhauser GJF, Bonen A, Spriet LL. High-intensity aerobic interval training increases fat and carbohydrate metabolic capacities in human skeletal muscle. Applied Physiology, Nutrition, and Metabolism. 2008;33(6):1112\u0026ndash;23. \u003c/li\u003e\n\u003cli\u003ePerry CGR, Talanian JL, Heigenhauser GJF, Spriet LL. The effects of training in hyperoxia vs. normoxia on skeletal muscle enzyme activities and exercise performance. J Appl Physiol. 2006;102(3):1022\u0026ndash;7. \u003c/li\u003e\n\u003cli\u003eMillet GP, Candau R, Fattori P, Bignet F, Varray A. Responses to different intermittent runs at velocity associated with. Canadian Journal of Applied Physiology. 2003;28(3):410\u0026ndash;23. \u003c/li\u003e\n\u003cli\u003eLee CL, Hsu WC, Cheng CF. Physiological adaptations to sprint interval training with matched exercise volume. Med Sci Sports Exerc. 2017;49(1):86\u0026ndash;95. \u003c/li\u003e\n\u003cli\u003eCampos F de S, Borszcz FK, Flores LJF, Barazetti LK, Teixeira AS, Hartmann Nunes RF, et al. HIIT Models in Addition to Training Load and Heart Rate Variability Are Related With Physiological and Performance Adaptations After 10-Weeks of Training in Young Futsal Players. Front Psychol. 2021 Jan 22;12. \u003c/li\u003e\n\u003cli\u003eMcGinley C, Bishop DJ. Influence of training intensity on adaptations in acid/base transport proteins, muscle buffer capacity, and repeated-sprint ability in active men. J Appl Physiol. 2016;121(6):1290\u0026ndash;305. \u003c/li\u003e\n\u003cli\u003eMilioni F, Zagatto A, Barbieri R, Andrade V, Santos J, Gobatto C, et al. Energy systems contribution in the running-based anaerobic sprint test. Int J Sports Med. 2017;38(03):226\u0026ndash;32. \u003c/li\u003e\n\u003cli\u003eMcGawley K, Bishop DJ. Oxygen uptake during repeated-sprint exercise. J Sci Med Sport. 2015;18(2):214\u0026ndash;8. \u003c/li\u003e\n\u003cli\u003eBuchheit M. The numbers will love you back in return \u0026mdash; I promise. Int J Sports Physiol Perform. 2016;11(4):551\u0026ndash;4. \u003c/li\u003e\n\u003cli\u003eBishop D, Edge J, Thomas C, Mercier J. Effects of high-intensity training on muscle lactate transporters and postexercise recovery of muscle lactate and hydrogen ions in women. AJP: Regulatory, Integrative and Comparative Physiology. 2008;295(6):R1991\u0026ndash;8. \u003c/li\u003e\n\u003cli\u003eSt\u0026ouml;ggl TL, Bj\u0026ouml;rklund G. High intensity interval training leads to greater improvements in acute heart rate recovery and anaerobic power as high volume low intensity training. Front Physiol. 2017;8(August):1\u0026ndash;8. \u003c/li\u003e\n\u003cli\u003eTabata I, Nishimura K, Kouzaki M, Hirai Y, Ogita F, Miyachi M, et al. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and ??VO2max. Medicine \u0026amp;amp Science in Sports \u0026amp;amp Exercise. 1996;28(10):1327\u0026ndash;30. \u003c/li\u003e\n\u003cli\u003eRavier G, Dugu\u0026eacute; B, Grappe F, Rouillon JD. Impressive anaerobic adaptations in elite karate athletes due to few intensive intermittent sessions added to regular karate training. Scand J Med Sci Sports. 2009;19(5):687\u0026ndash;94. \u003c/li\u003e\n\u003cli\u003eMilioni F, Azevedo RA, Zagatto AM, Millet GY. Time Course of Recovery after Cycling Repeated Sprints. Med Sci Sports Exerc. 2021 Feb 1;53(2):413\u0026ndash;20. \u003c/li\u003e\n\u003cli\u003eKinnunen JV, Piitulainen H, Piirainen JM. Neuromuscular adaptations to short-term high-intensity interval training in female ice hockey players. J Strength Cond Res. 2017;1. \u003c/li\u003e\n\u003cli\u003eVia\u0026ntilde;o-Santasmarinas J, Rey E, Carballeira S, Padr\u0026oacute;n-Cabo A. Effects of high-intensity interval training with different interval durations on physical performance in handball players. J Strength Cond Res. 2018;32(12):3389\u0026ndash;97. \u003c/li\u003e\n\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":"sport-sciences-for-health","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ssfh","sideBox":"Learn more about [Sport Sciences for Health](http://link.springer.com/journal/11332)","snPcode":"11332","submissionUrl":"https://submission.nature.com/new-submission/11332/3","title":"Sport Sciences for Health","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"neuromuscular fatigue, central fatigue, peripheral fatigue, sport performance, repeated sprint ability","lastPublishedDoi":"10.21203/rs.3.rs-3897583/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3897583/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003ePurpose:\u003c/strong\u003e High-intensity long-interval training (long-HIIT; interval≥1 min; intensity 85%-100% of maximal oxygen uptake [V̇O\u003csub\u003e2\u003c/sub\u003emax]) is often applied for cardiorespiratory adaptations, however long-HIIT can also challenge the anaerobic and neuromuscular systems. Therefore, this study aimed to investigate the effects of 4-week long-HIIT (11 sessions) on anaerobic capacity, repeated sprint ability (RSA), and neuromuscular function.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods:\u003c/strong\u003e Twenty active men (V̇O\u003csub\u003e2\u003c/sub\u003emax: 44.8±5.3 mL.kg\u003csup\u003e-1\u003c/sup\u003e.min\u003csup\u003e-1\u003c/sup\u003e) performed an incremental running test (T\u003csub\u003eINC\u003c/sub\u003e), a supramaximal test consisting in running until the task failure at 115% of maximum velocity achieved in T\u003csub\u003eINC\u003c/sub\u003e (V\u003csub\u003eINC\u003c/sub\u003e) for anaerobic capacity determination, and a RSA test (2×6×35-m all-out sprints) Pre- and Post-HIIT. Before and after RSA, the neuromuscular function was assessed with counter movement jumps (CMJ) and knee extensors maximal isometric voluntary contractions (MVC) with femoral nerve electrical stimulation. Long-HIIT consisted of 10×1-min runs at 90% of V\u003csub\u003eINC\u003c/sub\u003e with 1-min recovery.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults:\u003c/strong\u003e Long-HIIT induced significant increase in V̇O\u003csub\u003e2\u003c/sub\u003emax (P=0.0001). Although anaerobic capacity did not change significantly, 60% of the participants improved above the smallest worthwhile change (0.2×standard deviation of Pre-HIIT). The changes in sprint performance over RSA was significantly less post-HIIT than pre (P=0.01). RSA induced significant drop of MVC, high frequency doublet, voluntary activation and CMJ performance at Pre- and Post-HIIT (P\u0026lt;0.01), however, the percentage of reduction from rest to fatigued conditions were not significantly altered at Post-HIIT compared to Pre.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e 11 sessions of long-HIIT over 4-week improve maximal aerobic power but not anaerobic capacity, and neuromuscular function. Yet, neuromuscular fatigue was similar despite greater speeds reached during RSA.\u0026nbsp;\u0026nbsp;\u003c/p\u003e","manuscriptTitle":"Effects of 4-week high intensity interval training on anaerobic capacity, repeated-sprints performance and neuromuscular function","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-31 15:16:31","doi":"10.21203/rs.3.rs-3897583/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-03-09T01:59:04+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-02-28T22:10:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"88f0fb77-98aa-480e-ab18-2f2d8c58c75b","date":"2024-02-07T16:03:00+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-02-07T14:44:09+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-01-27T14:46:31+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-01-27T14:46:31+00:00","index":"","fulltext":""},{"type":"submitted","content":"Sport Sciences for Health","date":"2024-01-25T14:54:09+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"sport-sciences-for-health","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ssfh","sideBox":"Learn more about [Sport Sciences for Health](http://link.springer.com/journal/11332)","snPcode":"11332","submissionUrl":"https://submission.nature.com/new-submission/11332/3","title":"Sport Sciences for Health","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e20027df-aef7-4d3e-b41b-2a2669a0e162","owner":[],"postedDate":"January 31st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-04-25T10:21:04+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-31 15:16:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3897583","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3897583","identity":"rs-3897583","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}