Heart rate variability and blood pressure response to low intensity  endurance exercise training  plus blood flow restriction in individuals with mild hypertension

Heart rate variability and blood pressure response to low intensity endurance exercise training plus blood flow restriction in individuals with mild hypertension | 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 Heart rate variability and blood pressure response to low intensity endurance exercise training plus blood flow restriction in individuals with mild hypertension Maryam Doustaki Zaboli, Siyavash joukar, Masoumeh Nozari, Soheil Aminizadeh, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5347658/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background: Considering the lack of sufficient information, this study examined the effects of low- intensity endurance exercise training alone and with blood flow restriction (BFR) on blood pressure, electrocardiogram (ECG), and heart rate variability (HRV) in individuals with mild hypertension. Methods: 43 participants aged 50 – 65 years with mild hypertension were divided into three groups including; endurance exercise with BFR (Ex+ BFR) endurance exercise only (Ex), and a control group (Con) Exercise training was performed three times a week for ten weeks. Before and after the training program, HRV, blood pressure, resting heart rate, and heart rate recovery time were measured and analyzed. Results: In both Ex and Ex + BFR groups, RMSSD, SDSD, HF (nu), SD1, and the SD1/SD2 ratio significantly increased but, SD2 and the LF/HF ratio decreased vs. control group. Changes in the aforementioned parameters in Ex + BFR group than in Ex group. In comparison to Ex group, Ex + BFR group showed a greater reduction in the QRS interval (15% vs. 12%) and heart rate (7.9% vs. 6.3%) (P < 0.05). Both Ex and Ex+BFR groups experienced a significant decrease in heart rate recovery time and blood pressure (P < 0.001 vs. Con group), with no significant differences between them. Conclusion: Low- intensity endurance training combined with blood flow restriction not only had no negative impact on blood pressure, HRV, heart rate recovery, and ECG parameters, but in long term, it may have more positive impact compared to exercise alone in individuals with mild hypertension. Heart rate variability endurance exercise training blood flow restriction mild hypertension Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Heart rate variability (HRV) refers to the variations in time intervals between consecutive heartbeats. These fluctuations indicate the balance between the sympathetic and parasympathetic branches of the autonomic nervous system (ANS) and are important indicators for assessing ANS function and overall health ( 1 ). Aging significantly impacts the ANS of the heart so in elderly individuals, sympathetic nervous system (SNS) activity increases while parasympathetic nervous system (PNS)activity decreases ( 2 ). With aging, the ability of the ANS to regulate heart rate declines, reducing HRV. HRV reduction increases the long-term risk of cardiovascular diseases such as atrial fibrillation, major adverse cardiac events, stroke, and mortality ( 3 ).In addition, HRV hase been reported to decreases in hypertensive individuals compared to normotensive people, autonomic nervous system plays a role in the development of hypertension( 4 ). Exercise has been usually used as a non-pharmacological intervention to improve cardiovascular function ( 5 ). Endurance exercises are one of the most effective interventions for enhancing cardiovascular performance and reducing risk factors associated with cardiovascular diseases. The benefits of these exercises include increased oxygen delivery due to increased capillary density, improved membrane permeability, higher levels of muscle myoglobin, and greater mitochondrial density( 6 , 7 ). Studies have shown that moderate-intensity endurance exercises can improve time-domain HRV parameters, including RMSSD (root mean square of the successive differences), pRR50 (percentage of successive RR intervals differing by more than 50 ms), and SDNN (standard deviation of NN intervals), and in this way lead to ANS homeostasis ( 5 ). Resistance training can also positively affect HRV, although its impact is less than endurance exercises. A study demonstrated that 24 weeks of intensive resistance training emphasizing vagal control reduced resting heart rate and increased HRV in elderly participants, thereby reducing the risk of cardiovascular diseases ( 8 ). Blood flow restriction (BFR) is a technique that partially restricts arterial blood flow to the muscles while completely blocking venous return. This method involves using bands or cuffs specifically placed on the proximal parts of the upper or lower limbs ( 9 ). BFR is used in conjunction with other training modalities, including aerobic and resistance exercises ( 10 ). The BFR training effects are comparable to or even better than high-intensity exercises, which is particularly beneficial for elderly individuals who cannot perform intense activities ( 11 ). Another study reported that 12 weeks of low-intensity resistance training with blood flow restriction reduced blood pressure in elderly adults but had no effects on HRV ( 12 ). Other studies mentioned that six weeks of walking with blood flow restriction improved the HRV time domain and reduced systolic blood pressure in middle-aged men ( 13 , 14 ). Considering that endurance exercise is more effective in improving cardiovascular function, combining this type of exercise with blood flow restriction may yield beneficial or harmful results due to increased nervous system stimulation and additional metabolic stress. Given the limited studies that have examined the effects of endurance training with blood flow restriction, further research is needed to explore the precise outcomes and mechanisms of this training model on the cardiovascular system across different durations and intensities in various populations. This study investigated the effects of ten weeks of endurance training on a cycle ergometer with blood flow restriction on HRV, ECG parameters, mean arterial pressure, resting heart rate, and the time to return to rest heart rate after exercise in individuals aged 50 to 65 with mild hypertension. 2. Materials and Methods 2.1 Participants Participants in this study were aged between 50 and 65 years and had body mass index (BMI) less than 30. The participants were visited by the cardiologist in the Javad-al-Aeme clinic in Kerman. Individuals were evaluated by 48-hour ambulatory blood pressure monitoring. Based on the Heart Association's guidelines, Systolic pressure of 130–139 mmHg and/or a diastolic pressure of 80–89 mmHg were considered as mild hypertension ( 15 ). The physician also conducted the necessary clinical examinations. Participants who met the study’s entry criteria and could adhere to the prescribed exercise protocol were chosen. These criteria included abstaining from regular exercise for the past six months, not using any medications that lower blood pressure or affect the cardiovascular system (to prevent potential influences on the study results), and not having any joint or bone diseases, liver, kidney, or pulmonary diseases, diabetes, obesity (BMI over 30 kg/m²), or specific conditions such as cancer and cardiovascular diseases. All participants were fully informed about the study’s procedures, objectives, and the potential risks and benefits associated with the exercise routines. They signed an informed consent form, indicating their complete understanding of the study’s scope and nature. The ethics committee of Kerman University of Medical Sciences reviewed and approved the study protocol (Ethics code: IR.KMU.AH.REC.1402.029 and IRCT code: 20230528058311N1). 2.2 Study Groups and Design The sample size was calculated using G*Power software version 3.1.9.2. Based on the information entered into the software [α error probability = 0.05, power (1-β error probability) = 0.95] and considering three groups in the study. Participants were selected and matched based on age and body mass index (BMI) less than 30, ensuring a gender-balanced cohort. They were then randomly divided into three groups: endurance exercise training (Ex, n = 15), endurance exercise training with blood flow restriction (Ex + BFR, n = 15), and a control group (Con, n = 13) (Fig. 1 ). For the group undergoing endurance exercise with blood flow restriction, a cuff was placed proximally on the thigh to apply the blood flow restriction. The complete arterial occlusion pressure for the femoral artery was estimated using the following formula ( 16 ). Lower body arterial occlusion pressure (mmHg) = (5.893 × thigh circumference) + (0.912 × systolic blood pressure) + (0.734 × diastolic blood pressure) − 220.046. The cuff pressure for performing endurance exercise with blood flow restriction was set to 30% of the complete arterial occlusion pressure (AOP) and was maintained constant throughout the exercise program. The exercise duration was increased by five to ten minutes each week. The control group maintained their usual lifestyle and were exposed to an exercise environment; however, they did not participate in any exercise activities. 2.3 Calculation of Mean Arterial Pressure The arterial blood pressure of participants was measured with a suitable cuff from the left arm for two times with an interval of 10 minutes, and the average of these two values ​​was considered as the basis of blood pressure in each session. The following formula is used to calculate Mean Arterial Pressure (MAP): MAP = DBP + 1/3(SBP-DBP) while SBP is systolic blood pressure and DBP is diastolic blood pressure. 2.4 Method of Measuring VO2 Peak Using the Astrand Test To estimate maximal oxygen consumption (VO 2Peak ) and determine aerobic capacity in patients, the Astrand test was used ( 17 ). Participants refrained from consuming alcohol, caffeinated products, smoking, and vigorous activity at least 12 hours before the test. The Astrand test involves participants cycling for six minutes against a constant load. This test is conducted on a cycle ergometer (Monark, Ergomedic 839 E, Sweden) coupled with a gas analyzer (Cortex, Metalyzer 3B, Germany) while participants pedal in a seated position. The test includes a steady-state resting period, two minutes of warm-up without load, followed by a constant protocol where participants must pedal at a rate of 50 ± 5 revolutions per minute for six minutes while maintaining a heart rate (HR) between 120 and 140 beats per minute (bpm) ( 18 ). Measurements included oxygen saturation (SpO2) using a pulse oximeter (Beurer, Germany), HR, oxygen uptake (VO2), and the respiratory exchange ratio (RER). The mean HR and output wattage were utilized to calculate the maximum oxygen consumption, with an age coefficient added to the final values ( 16 ). A test was considered successful if the participant completed the 6-minute test with HRs maintained between 120 and 140 bpm. 2.5 Training protocol The training program lasted for 10 weeks, with three sessions per week on cycle ergometer. Each session included a 10-minute warm-up before exercise and a 10-minute cool-down at the end. The initial exercise duration was 20 minutes, performed at an intensity of 50–60% VO2 peak, which was matched to heart rate. The exercise duration was gradually increased by 5–10 minutes per session, reaching a maximum of 55 minutes by the tenth week. Additionally, exercise intensity was adjusted every two weeks based on heart rate, which was calibrated to 50–60% of VO2 peak, and according to the Rating of Perceived Exertion (RPE) scale, which measures the difficulty and intensity of physical activity. For the group with blood flow restriction, the restriction was adjusted or removed based on the RPE as needed and then reapplied. 2.6 Measurement of Heart Rate Recovery Time During the first training session, the resting heart rate was measured using the Polar Unite smartwatch. After completing the exercise in the initial session, the time taken for the heart rate to return to the resting rate was recorded with a stopwatch. Following a ten-week exercise program, the time to return to the resting heart rate was recorded again during the final training session. This recovery time was documented and compared for both the Ex and Ex + BFR groups at baseline and after the final training session. 2.7 ECG recording and HRV assessment Before the exercise program began and 24 hours after its completion, participants were instructed to refrain from consuming caffeinated beverages for 24 hours before measurements and to avoid non-routine physical activity for 48 hours beforehand. During the HRV recording, all individuals were asked to remain silent and breathe naturally. The recording took place with the participant in a supine position after 5 minutes of rest, at a room temperature of 25°C, for 10 minutes. In our study, Heart Rate Variability (HRV) was measured using a comprehensive approach that included both time-domain and frequency-domain analyses. Participants were monitored using an electrocardiogram (ECG) device, specifically employing the lead II electrode from a Power Lab data acquisition system (ADINSTRUMENTS, New South Wales, Australia). This system automatically detected R-waves and classified heartbeats as either normal or ectopic, which is a crucial step for accurate HRV assessment. For the time-domain analysis, key HRV metrics were calculated, including the Mean RR Interval (the average time between consecutive heartbeats), SDSD (Standard Deviation of Successive Differences, measuring the variation in time intervals between heartbeats), PRR50 (the proportion of RR intervals differing by more than 50 ms from the preceding interval), and RMSSD (the root mean square of successive differences between normal heartbeats). These parameters provide insights into overall heart rate variability and the influence of the autonomic nervous system on the heart, particularly in terms of PNS. This method quantified the distribution of absolute and relative power across various frequency bands. The Low Frequency (LF) band, ranging from 0.04 to 0.15 Hz, is generally associated with both SNS and PNS activity, while the High Frequency (HF) band, extending from 0.15 to 0.4 Hz, predominantly reflects parasympathetic (vagal) activity, which is linked to different components of autonomic regulation. Nonlinear indices, such as SD1 and SD2, were also used in the HRV analysis and assessed through Poincaré plot methods. SD1 reflects short-term variations in HRV, primarily influenced by PNS activity, focusing on immediate heart rate changes. SD2 indicates long-term HRV variability, associated with low-frequency power and baroreceptor sensitivity (BRS), illustrating the balance between SNS and PNS activities. The SD1/SD2 ratio is crucial for evaluating the randomness and balance of changes within the nervous system, providing a detailed analysis of cardiac health and stress levels. After data collection, the values were analyzed to assess the autonomic balance between SNS and PNS activities. This phase included comparing frequency-domain measures, such as the LF/HF ratio, which aids in understanding physiological responses to stress and cardiovascular health. All analyses were performed using HRV analysis software provided by Lab Chart 8, which allowed for a thorough evaluation of autonomic function by analyzing beat-to-beat interval variability. 2.8 ECG Parameters : The QT interval measures the time between the start of the Q wave and the end of the T wave, representing both ventricular depolarization and repolarization. QTc (Corrected QT Interval) is adjusted to account for variations in heart rate, QRS Interval; the duration of the QRS complex, which represents the time taken for ventricular depolarization. This interval is measured from the beginning of the Q wave to the end of the S wave, the Tpeak-Tend Interval; the interval from the peak of the T wave to the end of the T wave. This measures the late repolarization phase of the ventricles and is often used as an indicator of arrhythmogenic risk, JT Interval; The interval between the end of the QRS complex (J point) and the peak of the T wave. It represents the time of ventricular repolarization without including the depolarization period. The PR interval is the time from the start of the P wave to the beginning of the QRS complex on an ECG, reflecting the duration of atrial depolarization and the delay in ventricular depolarization. To calculate the percentage changes in HRV, ECG, and mean arterial pressure variables, the following formula was used: Percentage Change = (Final Value − Initial Value​/ Initial Value) ×100 2.9 Statistical analysis The statistical analyses were performed using Prism version 9 software. Data were presented as mean ± SEM. First, normality of the data was assessed using the Shapiro-Wilk test, and homogeneity of regression slopes was confirmed. Then, one-way ANOVA was used to compare pre-intervention values, as well as post-intervention values between groups. If significant differences were found between groups, Tukey's post-hoc tests were conducted to determine the specific differences between the groups. Paired t-tests were used to analyze intra-group changes in response to the intervention. 3. Results 3.1 Mean arterial pressure : The results of the one-way ANOVA indicated a significant difference in the percentage changes in mean arterial pressure among the groups [F (2, 40) = 27, P < 0.001]. Post hoc analyses revealed that mean arterial pressure was significantly reduced by 11% in the Ex group and by 13% in the Ex + BFR group compared to the Con group (P < 0.001). No significant difference was observed between the Ex and Ex + BFR groups (Fig. 2 -a). According to paired t-tests, mean arterial pressure decreased significantly in both the Ex (P < 0.001, t = 7.3) and Ex + BFR (P < 0.001, t = 9.1) groups after the intervention (Fig. 2 -b). 3.2 Heart rate recovery time Paired t-tests demonstrated a significant decrease in heart rate recovery time (the time required for the heart rate to return to resting levels after exercise) in the Ex-group from the first to the last session (P < 0.001, t = 11). This decrease was also significant in the Ex + BFR group (P < 0.001, t = 15, Fig. 3 ). 3.3 HRV parameters At the beginning of the study, there were no significant differences between different HRV parameters across the groups. The control individuals who did not participate in the exercise program did not show significant changes in any of the variables at the end of the study compared with initial values. The One-way ANOVA analysis indicated significant differences in the percentage changes of RMSSD and SDSD between groups [F (2, 40) = 9.7, P < 0.001]. Post-hoc analyses revealed that RMSSD and SDSD significantly increased by 13% in the Ex-group and 14% in the Ex + BFR group compared to Con group (P < 0.01 and P < 0.001, respectively) (Fig. 4 -a, c), No significant difference was found between the Ex and Ex + BFR groups. Paired t-test analysis showed that RMSSD and SDSD significantly increased after intervention in both the Ex (P < 0.001, t = 11) and Ex + BFR (P < 0.001, t = 4.3) groups (Fig. 4 -b, d). The percentage of successive R–R intervals that differ by more than 50 ms as an indicator for PNS activity was also assessed and reported as pRR50. These parameters did not show significance between groups [F (2, 40) = 0.097, P = 0.907], and did not change after intervention (P > 0.05) (Fig. 4 -e, f) The result of LF (nu) changes analysis showed no significant changes between groups [F (2,40) = 0.13, P = 0.881, Fig. 5 -a]. The paired t-test detected a significant change in LF (nu) in the Ex + BFR group (P > 0.05, t = 2.2) from the pre-test to the post-test, but there is no significant change in the Ex-group (P = 0.77, t = 1.9, Fig. 5 -b). The differences between HF (nu) changes were significant between the groups [F (2, 40) = 7.6, P = 0.002]. Tukey post-hoc analyses showed that HF (nu) significantly increased by 16% in the Ex group (P = 0.011) and by 19% in the Ex + BFR group (P = 0.002) compared to Con group. No significant difference was found between the Ex and Ex + BFR groups (P = 0.788, Fig. 5 -c). HF (nu) increased significantly in both the Ex (P = 0.017, t = 2.7) and Ex + BFR (P < 0.001, t = 4.5) groups from the pre-test to the post-test (Fig. 5 -d). The LF/HF ratio is utilized to appraise the SNS versus PNS activity ratio. The analysis showed significant differences between groups [F (2, 40) = 6.4, P = 0.004], decreasing by 19% in the Ex group (P = 0.013) and by 21% in the Ex + BFR group (P = 0.007) compared to Con. No significant difference was found between the Ex and Ex + BFR groups (P = 0.963, Fig. 5 -e). This parameter decreased significantly in both the Ex (P = 0.003, t = 3.6) and Ex + BFR (P = 0.004, t = 3.5) groups from the pre-test to the post-test (Fig. 5 -f). Significant differences were observed in the percentage changes of SD1(short-term HRV and index of PNS modulation) between groups [F (2, 40) = 15, P < 0.001]. Post-hoc analyses showed that SD1 increased significantly by 23% in the Ex group (P < 0.001) and by 25% in the Ex + BFR group (P < 0.001) compared to Con group. No significant difference was found between the Ex and Ex + BFR groups (P = 0.877, Fig. 6 -a). SD1 significantly increased in both the Ex (P < 0.001, t = 8.7) and Ex + BFR (P < 0.001, t = 7) groups after the intervention (Fig. 6 -b). For SD2 (long-term HRV that represents the autonomous system activity), significant differences were found between groups [F (2, 40) = 6.6, P = 0.003]. SD2 decreased significantly by 14% in the Ex group (P = 0.012) and by 15% in the Ex + BFR group (P = 0.005) compared to Con group. No significant difference was found between the Ex and Ex + BFR groups (P = 0.951, Fig. 6 -c). Paired t-tests also revealed significant decreases in SD2 in both the Ex (P = 0.005, t = 3.3) and Ex + BFR (P = 0.006, t = 3.3) groups after the intervention (Fig. 6 -d). The SD1/SD2 ratio were shown significant differences between groups [F (2, 40) = 9.5, P < 0.001, Fig. 6 -e]. Post-hoc analyses showed that SD1/SD2 increased significantly by 44% in the Ex group (P = 0.005) and by 55% in the Ex + BFR group (P < 0.001) compared to Con group. In addition, pair t-test showed significant increase of SD1/SD2 in both the Ex (P < 0.001, t = 5.9) and Ex + BFR [P < 0.001, t = 7.1] groups after intervention (Fig. 6 -f). 3.4 ECG parameters: The ECG analysis revealed significant differences among the groups in the PR interval [F (2, 40) = 5.5, P = 0.008]. Both the Ex and Ex + BFR groups showed a significant 4% increase compared to the Con group (P < 0.05), with no significant difference between the Ex and Ex + BFR groups (Fig. 7 -a). Additionally, both the Ex and Ex + BFR groups demonstrated a significant increase in the PR interval after intervention compared to pre-intervention (P < 0.05, t = 2.6 and P < 0.01, t = 3.9, respectively, Fig. 7 -b). Significant differences were also observed in the QRS interval [F (2, 40) = 8.1, P = 0.001], in the Ex and Ex + BFR groups compared to the Con group (Ex: 12% reduction, P = 0.010 and Ex + BFR: 15% reduction, P = 0.001). No significant difference was found between the Ex and Ex + BFR groups (Fig. 7 -c). Both groups experienced significant reductions in the QRS interval after the intervention [Ex: P < 0.001, t = 5.3 and Ex + BFR: P < 0.001, t = 5, Fig. 7 -d]. For heart rate, significant differences were observed [F (2,40) = 8.3, P < 0.001], and the Ex and Ex + BFR groups showed significant reductions compared to the Con group (6.3% reduction with P = 0.009 and 7.9% reduction with P = 0.001, respectively). No significant difference was found between the Ex and Ex + BFR groups (Fig. 7 -e). Both groups exhibited significant decreases in heart rate after intervention [Ex: P = 0.018, t = 2.7 and Ex + BFR: P < 0.001, t = 7.8, Fig. 7 -f]. No significant differences were observed for the QTc, JT interval, and the post-intervention changes were not statistically significant (Fig. 7 -g, h). Additionally, the Tpeak-Tend interval did not exhibit any significant changes following the intervention (graph not shown). 4. Discussion Our study aimed to evaluate the effects and comparison of ten weeks of low- intensity endurance exercise training alone and in combination with blood flow restriction (BFR), on heart rate variability (HRV), electrocardiogram (ECG) parameters, blood pressure, and heart rate recovery time following exercise in middle/early old individuals with mild hypertension. The results indicated that both types of exercise led to improvements in HRV and ECG parameters, as well as reductions in blood pressure and heart rate recovery time. However, the group performing exercise with blood flow restriction demonstrated greater improvements in some indices in comparison to corresponding baselines. One notable finding was the increase in time-domain HRV parameters, such as Standard Deviation of Successive Differences (SDSD) and Root Mean Square of Successive Differences (RMSSD), in both endurance exercise groups (with and without BFR) after the training period. An increase in SDSD reflects greater variability in the intervals between heartbeats, indicating improved autonomic control of the heart. The increase in RMSSD signifies enhanced parasympathetic activity, which helps with stress reduction and improvement of heart function and indicates better autonomic-cardiac regulation and a reduced risk of cardiovascular diseases. Studies on participants performing moderate-intensity exercise confirm that these exercises significantly increase RMSSD and SDSD ( 19 ). Consistent with our findings, human studies suggest that walking exercises with blood flow restriction can improve HRV and increase RMSSD, reflecting better heart rate regulation ( 13 , 14 ). However, studies on professional athletes undergoing high-intensity resistance and aerobic training have observed a decrease in RMSSD and SDSD, which may be attributed to the excessive stress of high-intensity exercises ( 20 ). Therefore, these findings indicate that the type and intensity of exercises should be carefully adjusted to optimize positive effects on HRV. Our study revealed that endurance exercise, with or without blood flow restriction, increases High Frequency (HF) and decreases the Low Frequency/High Frequency (LF/HF) ratio, with more pronounced changes observed in the group with blood flow restriction. Similar studies including research on aerobic exercise in animal models ( 21 ) and blood flow restriction exercises in human studies( 13 ), showed increase HF and decrease LF/HF, reflecting improved parasympathetic responses and reduced sympathetic stress. Conversely, an animal study found that high-intensity interval training increased LF/HF ( 22 ), and a human study found that resistance training increased LF/HF and decreased HF ( 8 ), which contrasts with our results. This discrepancy may be due to differences in the type and intensity of interventions. Another result of this study was the increase in SD1, decrease in SD2, and increase in SD1/SD2 in both the Ex and Ex + BFR groups, with more pronounced changes in the Ex + BFR group. An increase in SD1 reflects improved short-term heart rate regulation and reduced sudden fluctuations, likely due to increased parasympathetic activity and stabilizing the autonomic system and heart rate ( 23 ). A decrease in SD2 indicates reduced long-term heart rate fluctuations, reflecting decreased chronic stress on the cardiovascular system ( 23 ). The increase in SD1/SD2 also suggests improved sympathovagal balance and an enhanced ability to respond to short-term heart rate changes ( 24 ). Our results indicate that the increase in SD1 in both groups reflects better parasympathetic activity and improved heart rate regulation, while the decrease in SD2 points to reduced sympathetic activity and long-term cardiac stress. The increase in SD1/SD2 in both groups signifies a better balance between parasympathetic and sympathetic activities and an improved cardiovascular status ( 25 ). The results of present study revealed that combination of low-intensity endurance training with blood flow restriction not only dose not an inhibitory role on the beneficial effects of exercise on HRV, but it can even strengthen it. In contrast to our results, animal studies have shown that high-intensity interval training increases sympathetic activity and reduces HRV( 22 ), and human studies have shown that resistance training increases sympathetic activity and reduces HRV ( 8 ). Additionally, a human study demonstrated that low-intensity exercise had no significant effect on HRV in elderly individuals with hypertension ( 26 ). It seems that the difference in results depends on the type, intensity, and duration of exercise, as well as the initial health status of individuals and animal species studied. Regarding ECG results, the increase in PR interval, and reduction in the time of QRS complex in both exercise groups may indicate improvement in cardiac electrical conduction following improving the balance of the autonomic system of the heart and cardiac responses. The reduction in QRS interval can be related to improvement of the ventricular electrical conductivity and reduction of time for impulse propagation and ventricular depolarization. In the blood flow restriction group, a greater reduction in QRS interval compared to pre-exercise levels may reflect the positive effects of blood flow restriction on ventricular conduction velocity. Several human studies that have previously investigated the effects of endurance exercise on ECG, have reported results consistent with our findings ( 27 , 28 ) Also in agreement with our findings, an animal study demonstrated that regular endurance exercise programs can enhance cardiac electrical function and reduce arrhythmias in rats with myocardial infarction ( 29 ). However, some studies that contradict our results have shown that intense and prolonged endurance exercise may increase the risk of cardiac arrhythmias in certain individuals ( 30 , 31 ). Additionally, it has been shown that intense and prolonged endurance exercise in individuals with underlying heart disease can exacerbate their condition ( 32 ). The discrepancy in these studies' findings appears to be due to differences in exercise intensity and the populations studied. The other finding of our study was a reduction in arterial pressure and improvement of heart rate recovery time in both the endurance exercise group with and without blood flow restriction (BFR) in middle-aged individuals with mild hypertension. These results are consistent with the findings of two meta-analyses on the impact of some exercises combined with BFR on cardiovascular health, which reported reductions in blood pressure and improvements in heart rate recovery time ( 33 , 34 ). Furthermore, according to the results of another meta-analysis that examined various types of exercises with positive effects on blood pressure, endurance exercise was identified as the most effective type for reducing blood pressure, which aligns with our findings ( 35 ). On the other hand, our results differ from some other research that has highlighted the potential negative effects of intense endurance training. For example, one study warned that high-intensity endurance training could lead to long-term cardiac damage and increase the risk of atrial fibrillation (a type of arrhythmia that can lead to serious heart problems and an increased risk of stroke) in individuals with a history of heart disease ( 20 ). Additionally, another study found that combining resistance training with BFR could increase blood pressure in some individuals with hypertension, which contrasts with the positive findings of the present study ( 36 ). The differences in these results may be attributed to variations in exercise intensity and the type of exercise used in combination with BFR. 5. Conclusion This study demonstrated that ten weeks of mild endurance exercise, as well as endurance exercise combined with blood flow restriction (Ex + BFR), significantly improved heart rate variability (HRV) and ECG parameters in individuals with mild hypertension. Both approaches imposed substantial benefits on HRV indices, ECG parameters, and blood pressure. While both methods were effective, the Ex + BFR approach yielded slightly greater improvements in HRV and certain cardiovascular measures compared to exercise alone. Overall, these findings suggest that combination of blood flow restriction with mild endurance training not only is not harmful but could provide additional benefits for cardiovascular health in comparison with endurance training alone. Declarations Ethics approval and consent to participate This study was approved by the ethics committee of Kerman University of Medical Sciences (Ethics code: IR.KMU.AH.REC.1402.029), Clinical trial number: IRCT: 20230528058311N1 Consent for publication Not Applicable Competing Interests The authors declare there is no conflict of interest Funding This research is supported by Kerman University of Medical Sciences and Bam University of Medical Sciences Author Contribution M.D.Z. contributed to writing the first draft of the manuscript, the initial drafting of the figures, and data collection and analysis.M.N. collaborated in writing and revising the results section, creating the figures, and analyzing the dataS.A. played a role in writing and revising the methods section and supervising the proper implementation of the exercise protocol.M.K. and Kh.M. acted as cardiology specialists in examining and selecting eligible participants for the study. Acknowledgement We want to thank the Kerman University of Medical Sciences for its collaboration. Data Availability The data will be available on reasonable request. References Sessa F, Anna V, Messina G, Cibelli G, Monda V, Marsala G, et al. Heart rate variability as predictive factor for sudden cardiac death. Aging. 2018;10(2):166. Fajemiroye JO, Cunha LCd, Saavedra-Rodríguez R, Rodrigues KL, Naves LM, Mourão AA, et al. Aging-induced biological changes and cardiovascular diseases. Biomed Res Int. 2018;2018(1):7156435. Garavaglia L, Gulich D, Defeo MM, Thomas Mailland J, Irurzun IM. The effect of age on the heart rate variability of healthy subjects. PLoS ONE. 2021;16(10):e0255894. Jadhav UM, Kadam SA. Heart Rate Variability, Blood Pressure Variability: What Is Their Significance in Hypertension. Hypertension and Cardiovascular Disease in Asia. Springer; 2022. pp. 139–47. Grässler B, Thielmann B, Böckelmann I, Hökelmann A. 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A longitudinal study of left atrial structure and function. Circulation: Arrhythmia Electrophysiol. 2018;11(5):e005598. Pagan LU, Damatto RL, Gomes MJ, Lima AR, Cezar MD, Damatto FC, et al. Low-intensity aerobic exercise improves cardiac remodelling of adult spontaneously hypertensive rats. J Cell Mol Med. 2019;23(9):6504–7. Engel LE, de Souza FLA, Giometti IC, Okoshi K, Mariano TB, Ferreira NZ, et al. The high-intensity interval training mitigates the cardiac remodeling in spontaneously hypertensive rats. Life Sci. 2022;308:120959. Davidson BL, Byrne KA, Rood BL, Edwards ES, Akers JD, Wenos DL, et al. Impact of Moderate Exercise Training on Heart Rate Variability in Obese Adults. J Clin Exerc Physiol. 2021;10(1):12–9. Castello V, Simões RP, Bassi D, Catai AM, Arena R, Borghi-Silva A. Impact of aerobic exercise training on heart rate variability and functional capacity in obese women after gastric bypass surgery. Obes Surg. 2011;21:1739–49. Yılmaz M, Kayançiçek H, Çekici Y. Heart rate variability: Highlights from hidden signals. J Integr Cardiol. 2018;4:1–8. Deng Y, Zeng X, Tang C, Hou X, Zhang Y, Shi L. The effect of exercise training on heart rate variability in patients with hypertension: A systematic review and meta-analysis. J Sports Sci. 2024:1–16. Dorey TW, O'Brien MW, Kimmerly DS. The influence of aerobic fitness on electrocardiographic and heart rate variability parameters in young and older adults. Auton Neurosci. 2019;217:66–70. de Andrade PE, Zangirolami-Raimundo J, Morais TC, De Abreu LC, Siqueira CE, Sorpreso ICE, et al. Cardiac behavior and heart rate variability in elderly hypertensive individuals during aerobic exercise: a non-randomized controlled study. Int J Environ Res Public Health. 2023;20(2):1292. Dor-Haim H, Lotan C, Horowitz M, Swissa M. Intensive exercise training improves cardiac electrical stability in myocardial‐infarcted rats. J Am Heart Association. 2017;6(7):e005989. Eijsvogels TM, Thompson PD. Exercise is medicine: at any dose? JAMA. 2015;314(18):1915–6. Sharma S, Merghani A, Mont L. Exercise and the heart: the good, the bad, and the ugly. Eur Heart J. 2015;36(23):1445–53. Lavie CJ, Arena R, Swift DL, Johannsen NM, Sui X, Lee D-c, et al. Exercise and the cardiovascular system: clinical science and cardiovascular outcomes. Circul Res. 2015;117(2):207–19. Wong V, Song JS, Bell ZW, Yamada Y, Spitz RW, Abe T, et al. Blood flow restriction training on resting blood pressure and heart rate: a meta-analysis of the available literature. J Hum Hypertens. 2022;36(8):738–43. Zhang T, Tian G, Wang X. Effects of low-load blood flow restriction training on hemodynamic responses and vascular function in older adults: A meta-analysis. Int J Environ Res Public Health. 2022;19(11):6750. Saco-Ledo G, Valenzuela PL, Ruiz‐Hurtado G, Ruilope LM, Lucia A. Exercise reduces ambulatory blood pressure in patients with hypertension: a systematic review and meta‐analysis of randomized controlled trials. J Am Heart Association. 2020;9(24):e018487. Domingos E, Polito MD. Blood pressure response between resistance exercise with and without blood flow restriction: A systematic review and meta-analysis. Life Sci. 2018;209:122–31. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5347658","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":372381894,"identity":"e241a95f-c3ae-4eac-9ec3-485ae73fdf71","order_by":0,"name":"Maryam Doustaki Zaboli","email":"","orcid":"","institution":"Kerman, University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Maryam","middleName":"Doustaki","lastName":"Zaboli","suffix":""},{"id":372381895,"identity":"17024657-8c45-424f-a9cd-b47489802b75","order_by":1,"name":"Siyavash joukar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwUlEQVRIiWNgGAWjYFCCA8xAwgaIGRsPkKIlDaSlgVgtDCAthyG6iVIv33j4sMHPPeft1rYfBtpSYxNNUIvBgWPJiT3PbidvO5MI1HIsLbeBoBaGM8YHeA7cTjY7ANTC2HCYsBb5hjPGB/8cOJdsdv4hkVoYDpwxTuY5cMDO7AaxtoD8YixzIDnB7AbQlgRi/CI/4/BhyTcH7OzNzqc/fPChxoYIh0kcAFOJYJUJBJWDAD/EVHuiFI+CUTAKRsHIBABgJEzlGmuZpwAAAABJRU5ErkJggg==","orcid":"","institution":"Physiology Research Center, Institute of Neuropharmacology","correspondingAuthor":true,"prefix":"","firstName":"Siyavash","middleName":"","lastName":"joukar","suffix":""},{"id":372381897,"identity":"080501df-a17a-4dd6-b4ce-eab06f502b78","order_by":2,"name":"Masoumeh Nozari","email":"","orcid":"","institution":"Kerman, University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Masoumeh","middleName":"","lastName":"Nozari","suffix":""},{"id":372381899,"identity":"870ef4a6-f5a2-4eb7-ac4a-7ae7e61b6aae","order_by":3,"name":"Soheil Aminizadeh","email":"","orcid":"","institution":"Kerman, University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Soheil","middleName":"","lastName":"Aminizadeh","suffix":""},{"id":372381901,"identity":"37ca45d4-a3f2-4a9a-83ee-37f4007daa97","order_by":4,"name":"Masoomeh Kahnooji","email":"","orcid":"","institution":"Kerman, University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Masoomeh","middleName":"","lastName":"Kahnooji","suffix":""},{"id":372381903,"identity":"096a4960-0143-444c-9a53-7c4ffc5d2f4e","order_by":5,"name":"Khadije Mohammadi","email":"","orcid":"","institution":"Kerman, University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Khadije","middleName":"","lastName":"Mohammadi","suffix":""}],"badges":[],"createdAt":"2024-10-28 13:53:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5347658/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5347658/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":69912761,"identity":"5fe02791-44fe-427f-96d8-f4bd3cee7906","added_by":"auto","created_at":"2024-11-26 14:07:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":109090,"visible":true,"origin":"","legend":"\u003cp\u003eStudy flow diagram. BMI; Body mass index, BP; Blood Pressure\u003c/p\u003e","description":"","filename":"Figure1.tif.png","url":"https://assets-eu.researchsquare.com/files/rs-5347658/v1/0320718fbeb86aef89937bfd.png"},{"id":69912762,"identity":"b2295bb6-e39e-460c-b627-b3537d756523","added_by":"auto","created_at":"2024-11-26 14:07:08","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":731501,"visible":true,"origin":"","legend":"\u003cp\u003eChanges the percentage of \u003cstrong\u003eMean arterial pressure (a) and mean arterial pressure \u003c/strong\u003ebefore and after the intervention (b) in the study groups; data are presented as mean ± SEM; * in comparison with Con; # in comparison with pre-intervention ***p\u0026lt;0.001 ###P\u0026lt;0.001. Con; Control group, Ex; Exercise training group, Ex+BFR; Exercise training +Blood flow restriction group.\u003c/p\u003e","description":"","filename":"Figure2.tif.png","url":"https://assets-eu.researchsquare.com/files/rs-5347658/v1/c9b98db4b18080d3ec6ce829.png"},{"id":69911908,"identity":"d5ddfdf7-6579-483f-911f-dfb3c9d9f4c8","added_by":"auto","created_at":"2024-11-26 13:59:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":665686,"visible":true,"origin":"","legend":"\u003cp\u003eChanges of heart rate recovery time (the time required for the heart rate to return to resting levels after exercise) (a) and Heart Rate recovery time after ten-week exercise program (b). Data are presented as mean ± SEM (n=20 for each group); ### p\u0026lt;0.001in comparison with Baseline. Con; Control group, Ex; Exercise training group, Ex+BFR; Exercise training +Blood flow restriction group.\u003c/p\u003e","description":"","filename":"Figure3.tif.png","url":"https://assets-eu.researchsquare.com/files/rs-5347658/v1/b64cf52b3a2a8b33c1fd7e78.png"},{"id":69911911,"identity":"8169e339-462a-44e5-8528-883f32e0314e","added_by":"auto","created_at":"2024-11-26 13:59:08","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1187537,"visible":true,"origin":"","legend":"\u003cp\u003eRMSSD (a) and SDSD (c) and PRR50 (e) before and after the intervention and changes in percentage of RMSSD (b) and SDSD (d) and PRR50 (f) in the study groups. Data are presented as mean ± SEM, *in comparison with Con, # in comparison with pre-intervention; **p\u0026lt;0.01, ###p\u0026lt;0.001. SDSD; The Standard Deviation of Successive Differences, RMSSD; The root mean square of successive differences between normal heart beats, pRR50; The percentage of successive R–R intervals that differ by more than 50 ms. Con; Control group, Ex; Exercise training group, Ex+BFR; Exercise training +Blood flow restriction group\u003c/p\u003e","description":"","filename":"Figure4.tif.png","url":"https://assets-eu.researchsquare.com/files/rs-5347658/v1/4c30c7ab1d397c7d5a4ec91b.png"},{"id":69911913,"identity":"c82f374f-1efc-4558-a0f0-00b976d5b1a9","added_by":"auto","created_at":"2024-11-26 13:59:08","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1113927,"visible":true,"origin":"","legend":"\u003cp\u003eLF, HF, and LF/HF before and after the intervention and changes in percentage of them in the study groups. Data are presented as mean ± SEM; * in comparison with Con; # in comparison with pre-intervention; *p\u0026lt;0.05 **p\u0026lt;0.01 #p\u0026lt;0.05, # #p\u0026lt;0.01, ### p\u0026lt;0.001, Low-frequency power (LF) and high-frequency power (HF) in normalized units (nu.) were displayed. Normalized units (nu.) Con; Control group, Ex; Exercise training group, Ex + BFR; Exercise training +Blood flow restriction group.\u003c/p\u003e","description":"","filename":"Figure5.tif.png","url":"https://assets-eu.researchsquare.com/files/rs-5347658/v1/5a54a5de66196da37dfe34cc.png"},{"id":69911914,"identity":"90790a77-a230-4894-9a7e-74abe3db0bf3","added_by":"auto","created_at":"2024-11-26 13:59:08","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1188698,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in percentage of SD1 (a), SD2 (c), and SD1/SD2 (e) and SD1 (b), SD2 (d), and SD1/SD2 (f) before and after the exercise intervention in the study groups. Data are presented as mean ± SEM); * in comparison with Con; # in comparison with pre *p\u0026lt;0.05 **p\u0026lt;0.01 ***p\u0026lt;0.001 ##P\u0026lt;0.05 ###P\u0026lt;0.001. SD1, SD2, the standard deviation of the Poincar′e plot perpendicular to (SD1) and along (SD2) the line of identity; SD1 is an index of short-term variability, and SD2 is an index of long-term variability, The SD1/SD2 ratio is instrumental in evaluating the randomness and balance of changes within the nervous system. Con; Control group, Ex; Exercise training group, Ex+BFR; Exercise training +Blood flow restriction group.\u003c/p\u003e","description":"","filename":"Figure6.tif.png","url":"https://assets-eu.researchsquare.com/files/rs-5347658/v1/9cba29131de2c3df7d373afc.png"},{"id":69911910,"identity":"890383c8-8c5d-4a7c-a51c-4d334e6ef8a7","added_by":"auto","created_at":"2024-11-26 13:59:08","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":1338407,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePR, QRS and JT intervals, QTC and heart rate\u003c/strong\u003e before and after the intervention and their percentage changes in the study groups. Data are presented as mean ± SEM; * in comparison with Con; # in comparison with pre-intervention *p\u0026lt;0.05 **p\u0026lt;0.01 #P\u0026lt;0.05 ##P\u0026lt;0.01 ### P\u0026lt;0.001 .PR interval: The time from the onset of the P wave to the start of the QRS complex, representing atrial depolarization and AV node conduction. QRS interval: The duration of ventricular depolarization, measured from the beginning of the Q wave to the end of the S wave. JT interval: The time from the end of the QRS complex to the end of the T wave, reflecting ventricular repolarization. QTc: The corrected QT interval for heart rate, representing the total time for ventricular depolarization and repolarization. Heart Rate: The number of heart beats per minute, typically measured via the R-R interval on the ECG Con; Control group, Ex; Exercise training group, Ex+BFR; Exercise training +Blood flow restriction group.\u003c/p\u003e","description":"","filename":"Figure7.tif.png","url":"https://assets-eu.researchsquare.com/files/rs-5347658/v1/fa45b5fbe6e26f89409572ee.png"},{"id":71351184,"identity":"811b960e-8d31-456e-9b3e-d854fe63c189","added_by":"auto","created_at":"2024-12-13 14:47:06","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6538139,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5347658/v1/c88efcb6-4890-4e88-baef-f1b885d1768c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Heart rate variability and blood pressure response to low intensity endurance exercise training plus blood flow restriction in individuals with mild hypertension","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eHeart rate variability (HRV) refers to the variations in time intervals between consecutive heartbeats. These fluctuations indicate the balance between the sympathetic and parasympathetic branches of the autonomic nervous system (ANS) and are important indicators for assessing ANS function and overall health (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e). Aging significantly impacts the ANS of the heart so in elderly individuals, sympathetic nervous system (SNS) activity increases while parasympathetic nervous system (PNS)activity decreases (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). With aging, the ability of the ANS to regulate heart rate declines, reducing HRV. HRV reduction increases the long-term risk of cardiovascular diseases such as atrial fibrillation, major adverse cardiac events, stroke, and mortality (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e).In addition, HRV hase been reported to decreases in hypertensive individuals compared to normotensive people, autonomic nervous system plays a role in the development of hypertension(\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e). Exercise has been usually used as a non-pharmacological intervention to improve cardiovascular function (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). Endurance exercises are one of the most effective interventions for enhancing cardiovascular performance and reducing risk factors associated with cardiovascular diseases. The benefits of these exercises include increased oxygen delivery due to increased capillary density, improved membrane permeability, higher levels of muscle myoglobin, and greater mitochondrial density(\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e). Studies have shown that moderate-intensity endurance exercises can improve time-domain HRV parameters, including RMSSD (root mean square of the successive differences), pRR50 (percentage of successive RR intervals differing by more than 50 ms), and SDNN (standard deviation of NN intervals), and in this way lead to ANS homeostasis (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). Resistance training can also positively affect HRV, although its impact is less than endurance exercises. A study demonstrated that 24 weeks of intensive resistance training emphasizing vagal control reduced resting heart rate and increased HRV in elderly participants, thereby reducing the risk of cardiovascular diseases (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e). Blood flow restriction (BFR) is a technique that partially restricts arterial blood flow to the muscles while completely blocking venous return. This method involves using bands or cuffs specifically placed on the proximal parts of the upper or lower limbs (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e). BFR is used in conjunction with other training modalities, including aerobic and resistance exercises (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). The BFR training effects are comparable to or even better than high-intensity exercises, which is particularly beneficial for elderly individuals who cannot perform intense activities (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). Another study reported that 12 weeks of low-intensity resistance training with blood flow restriction reduced blood pressure in elderly adults but had no effects on HRV (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e). Other studies mentioned that six weeks of walking with blood flow restriction improved the HRV time domain and reduced systolic blood pressure in middle-aged men (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e). Considering that endurance exercise is more effective in improving cardiovascular function, combining this type of exercise with blood flow restriction may yield beneficial or harmful results due to increased nervous system stimulation and additional metabolic stress. Given the limited studies that have examined the effects of endurance training with blood flow restriction, further research is needed to explore the precise outcomes and mechanisms of this training model on the cardiovascular system across different durations and intensities in various populations. This study investigated the effects of ten weeks of endurance training on a cycle ergometer with blood flow restriction on HRV, ECG parameters, mean arterial pressure, resting heart rate, and the time to return to rest heart rate after exercise in individuals aged 50 to 65 with mild hypertension.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Participants\u003c/h2\u003e \u003cp\u003eParticipants in this study were aged between 50 and 65 years and had body mass index (BMI) less than 30. The participants were visited by the cardiologist in the Javad-al-Aeme clinic in Kerman. Individuals were evaluated by 48-hour ambulatory blood pressure monitoring. Based on the Heart Association's guidelines, Systolic pressure of 130\u0026ndash;139 mmHg and/or a diastolic pressure of 80\u0026ndash;89 mmHg were considered as mild hypertension (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). The physician also conducted the necessary clinical examinations. Participants who met the study\u0026rsquo;s entry criteria and could adhere to the prescribed exercise protocol were chosen. These criteria included abstaining from regular exercise for the past six months, not using any medications that lower blood pressure or affect the cardiovascular system (to prevent potential influences on the study results), and not having any joint or bone diseases, liver, kidney, or pulmonary diseases, diabetes, obesity (BMI over 30 kg/m\u0026sup2;), or specific conditions such as cancer and cardiovascular diseases. All participants were fully informed about the study\u0026rsquo;s procedures, objectives, and the potential risks and benefits associated with the exercise routines. They signed an informed consent form, indicating their complete understanding of the study\u0026rsquo;s scope and nature. The ethics committee of Kerman University of Medical Sciences reviewed and approved the study protocol (Ethics code: IR.KMU.AH.REC.1402.029 and IRCT code: 20230528058311N1).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Study Groups and Design\u003c/h2\u003e \u003cp\u003eThe sample size was calculated using G*Power software version 3.1.9.2. Based on the information entered into the software [α error probability\u0026thinsp;=\u0026thinsp;0.05, power (1-β error probability)\u0026thinsp;=\u0026thinsp;0.95] and considering three groups in the study. Participants were selected and matched based on age and body mass index (BMI) less than 30, ensuring a gender-balanced cohort. They were then randomly divided into three groups: endurance exercise training (Ex, n\u0026thinsp;=\u0026thinsp;15), endurance exercise training with blood flow restriction (Ex\u0026thinsp;+\u0026thinsp;BFR, n\u0026thinsp;=\u0026thinsp;15), and a control group (Con, n\u0026thinsp;=\u0026thinsp;13) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). For the group undergoing endurance exercise with blood flow restriction, a cuff was placed proximally on the thigh to apply the blood flow restriction. The complete arterial occlusion pressure for the femoral artery was estimated using the following formula (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eLower body arterial occlusion pressure (mmHg) = (5.893 \u0026times; thigh circumference) + (0.912 \u0026times; systolic blood pressure) + (0.734 \u0026times; diastolic blood pressure) \u0026minus;\u0026thinsp;220.046.\u003c/p\u003e \u003cp\u003eThe cuff pressure for performing endurance exercise with blood flow restriction was set to 30% of the complete arterial occlusion pressure (AOP) and was maintained constant throughout the exercise program. The exercise duration was increased by five to ten minutes each week. The control group maintained their usual lifestyle and were exposed to an exercise environment; however, they did not participate in any exercise activities.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Calculation of Mean Arterial Pressure\u003c/h2\u003e \u003cp\u003eThe arterial blood pressure of participants was measured with a suitable cuff from the left arm for two times with an interval of 10 minutes, and the average of these two values ​​was considered as the basis of blood pressure in each session. The following formula is used to calculate Mean Arterial Pressure (MAP): MAP\u0026thinsp;=\u0026thinsp;DBP\u0026thinsp;+\u0026thinsp;1/3(SBP-DBP) while SBP is systolic blood pressure and DBP is diastolic blood pressure.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Method of Measuring VO2 Peak Using the Astrand Test\u003c/h2\u003e \u003cp\u003eTo estimate maximal oxygen consumption (VO\u003csub\u003e2Peak\u003c/sub\u003e) and determine aerobic capacity in patients, the Astrand test was used (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). Participants refrained from consuming alcohol, caffeinated products, smoking, and vigorous activity at least 12 hours before the test. The Astrand test involves participants cycling for six minutes against a constant load. This test is conducted on a cycle ergometer (Monark, Ergomedic 839 E, Sweden) coupled with a gas analyzer (Cortex, Metalyzer 3B, Germany) while participants pedal in a seated position. The test includes a steady-state resting period, two minutes of warm-up without load, followed by a constant protocol where participants must pedal at a rate of 50\u0026thinsp;\u0026plusmn;\u0026thinsp;5 revolutions per minute for six minutes while maintaining a heart rate (HR) between 120 and 140 beats per minute (bpm) (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). Measurements included oxygen saturation (SpO2) using a pulse oximeter (Beurer, Germany), HR, oxygen uptake (VO2), and the respiratory exchange ratio (RER). The mean HR and output wattage were utilized to calculate the maximum oxygen consumption, with an age coefficient added to the final values (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e). A test was considered successful if the participant completed the 6-minute test with HRs maintained between 120 and 140 bpm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Training protocol\u003c/h2\u003e \u003cp\u003eThe training program lasted for 10 weeks, with three sessions per week on cycle ergometer. Each session included a 10-minute warm-up before exercise and a 10-minute cool-down at the end. The initial exercise duration was 20 minutes, performed at an intensity of 50\u0026ndash;60% VO2 peak, which was matched to heart rate. The exercise duration was gradually increased by 5\u0026ndash;10 minutes per session, reaching a maximum of 55 minutes by the tenth week. Additionally, exercise intensity was adjusted every two weeks based on heart rate, which was calibrated to 50\u0026ndash;60% of VO2 peak, and according to the Rating of Perceived Exertion (RPE) scale, which measures the difficulty and intensity of physical activity. For the group with blood flow restriction, the restriction was adjusted or removed based on the RPE as needed and then reapplied.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Measurement of Heart Rate Recovery Time\u003c/h2\u003e \u003cp\u003eDuring the first training session, the resting heart rate was measured using the Polar Unite smartwatch. After completing the exercise in the initial session, the time taken for the heart rate to return to the resting rate was recorded with a stopwatch. Following a ten-week exercise program, the time to return to the resting heart rate was recorded again during the final training session. This recovery time was documented and compared for both the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups at baseline and after the final training session.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7 ECG recording and HRV assessment\u003c/h2\u003e \u003cp\u003eBefore the exercise program began and 24 hours after its completion, participants were instructed to refrain from consuming caffeinated beverages for 24 hours before measurements and to avoid non-routine physical activity for 48 hours beforehand. During the HRV recording, all individuals were asked to remain silent and breathe naturally. The recording took place with the participant in a supine position after 5 minutes of rest, at a room temperature of 25\u0026deg;C, for 10 minutes. In our study, Heart Rate Variability (HRV) was measured using a comprehensive approach that included both time-domain and frequency-domain analyses. Participants were monitored using an electrocardiogram (ECG) device, specifically employing the lead II electrode from a Power Lab data acquisition system (ADINSTRUMENTS, New South Wales, Australia). This system automatically detected R-waves and classified heartbeats as either normal or ectopic, which is a crucial step for accurate HRV assessment. For the time-domain analysis, key HRV metrics were calculated, including the Mean RR Interval (the average time between consecutive heartbeats), SDSD (Standard Deviation of Successive Differences, measuring the variation in time intervals between heartbeats), PRR50 (the proportion of RR intervals differing by more than 50 ms from the preceding interval), and RMSSD (the root mean square of successive differences between normal heartbeats). These parameters provide insights into overall heart rate variability and the influence of the autonomic nervous system on the heart, particularly in terms of PNS. This method quantified the distribution of absolute and relative power across various frequency bands. The Low Frequency (LF) band, ranging from 0.04 to 0.15 Hz, is generally associated with both SNS and PNS activity, while the High Frequency (HF) band, extending from 0.15 to 0.4 Hz, predominantly reflects parasympathetic (vagal) activity, which is linked to different components of autonomic regulation. Nonlinear indices, such as SD1 and SD2, were also used in the HRV analysis and assessed through Poincar\u0026eacute; plot methods. SD1 reflects short-term variations in HRV, primarily influenced by PNS activity, focusing on immediate heart rate changes. SD2 indicates long-term HRV variability, associated with low-frequency power and baroreceptor sensitivity (BRS), illustrating the balance between SNS and PNS activities. The SD1/SD2 ratio is crucial for evaluating the randomness and balance of changes within the nervous system, providing a detailed analysis of cardiac health and stress levels. After data collection, the values were analyzed to assess the autonomic balance between SNS and PNS activities. This phase included comparing frequency-domain measures, such as the LF/HF ratio, which aids in understanding physiological responses to stress and cardiovascular health. All analyses were performed using HRV analysis software provided by Lab Chart 8, which allowed for a thorough evaluation of autonomic function by analyzing beat-to-beat interval variability.\u003c/p\u003e \u003cp\u003e \u003cb\u003e2.8 ECG Parameters\u003c/b\u003e: The QT interval measures the time between the start of the Q wave and the end of the T wave, representing both ventricular depolarization and repolarization. QTc (Corrected QT Interval) is adjusted to account for variations in heart rate, QRS Interval; the duration of the QRS complex, which represents the time taken for ventricular depolarization. This interval is measured from the beginning of the Q wave to the end of the S wave, the Tpeak-Tend Interval; the interval from the peak of the T wave to the end of the T wave. This measures the late repolarization phase of the ventricles and is often used as an indicator of arrhythmogenic risk, JT Interval; The interval between the end of the QRS complex (J point) and the peak of the T wave. It represents the time of ventricular repolarization without including the depolarization period. The PR interval is the time from the start of the P wave to the beginning of the QRS complex on an ECG, reflecting the duration of atrial depolarization and the delay in ventricular depolarization. To calculate the percentage changes in HRV, ECG, and mean arterial pressure variables, the following formula was used: Percentage Change = (Final Value\u0026thinsp;\u0026minus;\u0026thinsp;Initial Value​/ Initial Value) \u0026times;100\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e2.9 Statistical analysis\u003c/h2\u003e \u003cp\u003eThe statistical analyses were performed using Prism version 9 software. Data were presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SEM. First, normality of the data was assessed using the Shapiro-Wilk test, and homogeneity of regression slopes was confirmed. Then, one-way ANOVA was used to compare pre-intervention values, as well as post-intervention values between groups. If significant differences were found between groups, Tukey's post-hoc tests were conducted to determine the specific differences between the groups. Paired t-tests were used to analyze intra-group changes in response to the intervention.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e3.1 Mean arterial pressure\u003c/b\u003e:\u003c/h2\u003e \u003cp\u003eThe results of the one-way ANOVA indicated a significant difference in the percentage changes in mean arterial pressure among the groups [F (2, 40)\u0026thinsp;=\u0026thinsp;27, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001]. Post hoc analyses revealed that mean arterial pressure was significantly reduced by 11% in the Ex group and by 13% in the Ex\u0026thinsp;+\u0026thinsp;BFR group compared to the Con group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001). No significant difference was observed between the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e-a). According to paired t-tests, mean arterial pressure decreased significantly in both the Ex (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;7.3) and Ex\u0026thinsp;+\u0026thinsp;BFR (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;9.1) groups after the intervention (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e-b).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Heart rate recovery time\u003c/h2\u003e \u003cp\u003ePaired t-tests demonstrated a significant decrease in heart rate recovery time (the time required for the heart rate to return to resting levels after exercise) in the Ex-group from the first to the last session (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;11). This decrease was also significant in the Ex\u0026thinsp;+\u0026thinsp;BFR group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;15, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.3 HRV parameters\u003c/h2\u003e \u003cp\u003eAt the beginning of the study, there were no significant differences between different HRV parameters across the groups. The control individuals who did not participate in the exercise program did not show significant changes in any of the variables at the end of the study compared with initial values.\u003c/p\u003e \u003cp\u003eThe One-way ANOVA analysis indicated significant differences in the percentage changes of RMSSD and SDSD between groups [F (2, 40)\u0026thinsp;=\u0026thinsp;9.7, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001]. Post-hoc analyses revealed that RMSSD and SDSD significantly increased by 13% in the Ex-group and 14% in the Ex\u0026thinsp;+\u0026thinsp;BFR group compared to Con group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01 and P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, respectively) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e-a, c), No significant difference was found between the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePaired t-test analysis showed that RMSSD and SDSD significantly increased after intervention in both the Ex (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;11) and Ex\u0026thinsp;+\u0026thinsp;BFR (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;4.3) groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e-b, d).\u003c/p\u003e \u003cp\u003eThe percentage of successive R\u0026ndash;R intervals that differ by more than 50 ms as an indicator for PNS activity was also assessed and reported as pRR50. These parameters did not show significance between groups [F (2, 40)\u0026thinsp;=\u0026thinsp;0.097, P\u0026thinsp;=\u0026thinsp;0.907], and did not change after intervention (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e-e, f)\u003c/p\u003e \u003cp\u003eThe result of LF (nu) changes analysis showed no significant changes between groups [F (2,40)\u0026thinsp;=\u0026thinsp;0.13, P\u0026thinsp;=\u0026thinsp;0.881, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e-a]. The paired t-test detected a significant change in LF (nu) in the Ex\u0026thinsp;+\u0026thinsp;BFR group (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05, t\u0026thinsp;=\u0026thinsp;2.2) from the pre-test to the post-test, but there is no significant change in the Ex-group (P\u0026thinsp;=\u0026thinsp;0.77, t\u0026thinsp;=\u0026thinsp;1.9, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e-b).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe differences between HF (nu) changes were significant between the groups [F (2, 40)\u0026thinsp;=\u0026thinsp;7.6, P\u0026thinsp;=\u0026thinsp;0.002]. Tukey post-hoc analyses showed that HF (nu) significantly increased by 16% in the Ex group (P\u0026thinsp;=\u0026thinsp;0.011) and by 19% in the Ex\u0026thinsp;+\u0026thinsp;BFR group (P\u0026thinsp;=\u0026thinsp;0.002) compared to Con group. No significant difference was found between the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups (P\u0026thinsp;=\u0026thinsp;0.788, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e-c). HF (nu) increased significantly in both the Ex (P\u0026thinsp;=\u0026thinsp;0.017, t\u0026thinsp;=\u0026thinsp;2.7) and Ex\u0026thinsp;+\u0026thinsp;BFR (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;4.5) groups from the pre-test to the post-test (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e-d).\u003c/p\u003e \u003cp\u003eThe LF/HF ratio is utilized to appraise the SNS versus PNS activity ratio. The analysis showed significant differences between groups [F (2, 40)\u0026thinsp;=\u0026thinsp;6.4, P\u0026thinsp;=\u0026thinsp;0.004], decreasing by 19% in the Ex group (P\u0026thinsp;=\u0026thinsp;0.013) and by 21% in the Ex\u0026thinsp;+\u0026thinsp;BFR group (P\u0026thinsp;=\u0026thinsp;0.007) compared to Con. No significant difference was found between the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups (P\u0026thinsp;=\u0026thinsp;0.963, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e-e). This parameter decreased significantly in both the Ex (P\u0026thinsp;=\u0026thinsp;0.003, t\u0026thinsp;=\u0026thinsp;3.6) and Ex\u0026thinsp;+\u0026thinsp;BFR (P\u0026thinsp;=\u0026thinsp;0.004, t\u0026thinsp;=\u0026thinsp;3.5) groups from the pre-test to the post-test (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e-f).\u003c/p\u003e \u003cp\u003eSignificant differences were observed in the percentage changes of SD1(short-term HRV and index of PNS modulation) between groups [F (2, 40)\u0026thinsp;=\u0026thinsp;15, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001]. Post-hoc analyses showed that SD1 increased significantly by 23% in the Ex group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and by 25% in the Ex\u0026thinsp;+\u0026thinsp;BFR group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) compared to Con group. No significant difference was found between the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups (P\u0026thinsp;=\u0026thinsp;0.877, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e-a). SD1 significantly increased in both the Ex (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;8.7) and Ex\u0026thinsp;+\u0026thinsp;BFR (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;7) groups after the intervention (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e-b).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor SD2 (long-term HRV that represents the autonomous system activity), significant differences were found between groups [F (2, 40)\u0026thinsp;=\u0026thinsp;6.6, P\u0026thinsp;=\u0026thinsp;0.003]. SD2 decreased significantly by 14% in the Ex group (P\u0026thinsp;=\u0026thinsp;0.012) and by 15% in the Ex\u0026thinsp;+\u0026thinsp;BFR group (P\u0026thinsp;=\u0026thinsp;0.005) compared to Con group. No significant difference was found between the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups (P\u0026thinsp;=\u0026thinsp;0.951, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e-c). Paired t-tests also revealed significant decreases in SD2 in both the Ex (P\u0026thinsp;=\u0026thinsp;0.005, t\u0026thinsp;=\u0026thinsp;3.3) and Ex\u0026thinsp;+\u0026thinsp;BFR (P\u0026thinsp;=\u0026thinsp;0.006, t\u0026thinsp;=\u0026thinsp;3.3) groups after the intervention (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e-d).\u003c/p\u003e \u003cp\u003eThe SD1/SD2 ratio were shown significant differences between groups [F (2, 40)\u0026thinsp;=\u0026thinsp;9.5, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e-e]. Post-hoc analyses showed that SD1/SD2 increased significantly by 44% in the Ex group (P\u0026thinsp;=\u0026thinsp;0.005) and by 55% in the Ex\u0026thinsp;+\u0026thinsp;BFR group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) compared to Con group. In addition, pair t-test showed significant increase of SD1/SD2 in both the Ex (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;5.9) and Ex\u0026thinsp;+\u0026thinsp;BFR [P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;7.1] groups after intervention (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e-f).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.4 ECG parameters:\u003c/h2\u003e \u003cp\u003eThe ECG analysis revealed significant differences among the groups in the PR interval [F (2, 40)\u0026thinsp;=\u0026thinsp;5.5, P\u0026thinsp;=\u0026thinsp;0.008]. Both the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups showed a significant 4% increase compared to the Con group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05), with no significant difference between the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e-a). Additionally, both the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups demonstrated a significant increase in the PR interval after intervention compared to pre-intervention (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05, t\u0026thinsp;=\u0026thinsp;2.6 and P\u0026thinsp;\u0026lt;\u0026thinsp;0.01, t\u0026thinsp;=\u0026thinsp;3.9, respectively, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e-b).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSignificant differences were also observed in the QRS interval [F (2, 40)\u0026thinsp;=\u0026thinsp;8.1, P\u0026thinsp;=\u0026thinsp;0.001], in the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups compared to the Con group (Ex: 12% reduction, P\u0026thinsp;=\u0026thinsp;0.010 and Ex\u0026thinsp;+\u0026thinsp;BFR: 15% reduction, P\u0026thinsp;=\u0026thinsp;0.001). No significant difference was found between the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e-c). Both groups experienced significant reductions in the QRS interval after the intervention [Ex: P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;5.3 and Ex\u0026thinsp;+\u0026thinsp;BFR: P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;5, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e-d].\u003c/p\u003e \u003cp\u003eFor heart rate, significant differences were observed [F (2,40)\u0026thinsp;=\u0026thinsp;8.3, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001], and the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups showed significant reductions compared to the Con group (6.3% reduction with P\u0026thinsp;=\u0026thinsp;0.009 and 7.9% reduction with P\u0026thinsp;=\u0026thinsp;0.001, respectively). No significant difference was found between the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e-e). Both groups exhibited significant decreases in heart rate after intervention [Ex: P\u0026thinsp;=\u0026thinsp;0.018, t\u0026thinsp;=\u0026thinsp;2.7 and Ex\u0026thinsp;+\u0026thinsp;BFR: P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, t\u0026thinsp;=\u0026thinsp;7.8, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e-f].\u003c/p\u003e \u003cp\u003eNo significant differences were observed for the QTc, JT interval, and the post-intervention changes were not statistically significant (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e-g, h). Additionally, the Tpeak-Tend interval did not exhibit any significant changes following the intervention (graph not shown).\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eOur study aimed to evaluate the effects and comparison of ten weeks of low- intensity endurance exercise training alone and in combination with blood flow restriction (BFR), on heart rate variability (HRV), electrocardiogram (ECG) parameters, blood pressure, and heart rate recovery time following exercise in middle/early old individuals with mild hypertension. The results indicated that both types of exercise led to improvements in HRV and ECG parameters, as well as reductions in blood pressure and heart rate recovery time. However, the group performing exercise with blood flow restriction demonstrated greater improvements in some indices in comparison to corresponding baselines.\u003c/p\u003e \u003cp\u003eOne notable finding was the increase in time-domain HRV parameters, such as Standard Deviation of Successive Differences (SDSD) and Root Mean Square of Successive Differences (RMSSD), in both endurance exercise groups (with and without BFR) after the training period. An increase in SDSD reflects greater variability in the intervals between heartbeats, indicating improved autonomic control of the heart. The increase in RMSSD signifies enhanced parasympathetic activity, which helps with stress reduction and improvement of heart function and indicates better autonomic-cardiac regulation and a reduced risk of cardiovascular diseases. Studies on participants performing moderate-intensity exercise confirm that these exercises significantly increase RMSSD and SDSD (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). Consistent with our findings, human studies suggest that walking exercises with blood flow restriction can improve HRV and increase RMSSD, reflecting better heart rate regulation (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHowever, studies on professional athletes undergoing high-intensity resistance and aerobic training have observed a decrease in RMSSD and SDSD, which may be attributed to the excessive stress of high-intensity exercises (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e). Therefore, these findings indicate that the type and intensity of exercises should be carefully adjusted to optimize positive effects on HRV.\u003c/p\u003e \u003cp\u003eOur study revealed that endurance exercise, with or without blood flow restriction, increases High Frequency (HF) and decreases the Low Frequency/High Frequency (LF/HF) ratio, with more pronounced changes observed in the group with blood flow restriction. Similar studies including research on aerobic exercise in animal models (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e) and blood flow restriction exercises in human studies(\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e), showed increase HF and decrease LF/HF, reflecting improved parasympathetic responses and reduced sympathetic stress. Conversely, an animal study found that high-intensity interval training increased LF/HF (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e), and a human study found that resistance training increased LF/HF and decreased HF (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e), which contrasts with our results. This discrepancy may be due to differences in the type and intensity of interventions.\u003c/p\u003e \u003cp\u003eAnother result of this study was the increase in SD1, decrease in SD2, and increase in SD1/SD2 in both the Ex and Ex\u0026thinsp;+\u0026thinsp;BFR groups, with more pronounced changes in the Ex\u0026thinsp;+\u0026thinsp;BFR group. An increase in SD1 reflects improved short-term heart rate regulation and reduced sudden fluctuations, likely due to increased parasympathetic activity and stabilizing the autonomic system and heart rate (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). A decrease in SD2 indicates reduced long-term heart rate fluctuations, reflecting decreased chronic stress on the cardiovascular system (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). The increase in SD1/SD2 also suggests improved sympathovagal balance and an enhanced ability to respond to short-term heart rate changes (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e). Our results indicate that the increase in SD1 in both groups reflects better parasympathetic activity and improved heart rate regulation, while the decrease in SD2 points to reduced sympathetic activity and long-term cardiac stress. The increase in SD1/SD2 in both groups signifies a better balance between parasympathetic and sympathetic activities and an improved cardiovascular status (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e). The results of present study revealed that combination of low-intensity endurance training with blood flow restriction not only dose not an inhibitory role on the beneficial effects of exercise on HRV, but it can even strengthen it. In contrast to our results, animal studies have shown that high-intensity interval training increases sympathetic activity and reduces HRV(\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e), and human studies have shown that resistance training increases sympathetic activity and reduces HRV (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e). Additionally, a human study demonstrated that low-intensity exercise had no significant effect on HRV in elderly individuals with hypertension (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e). It seems that the difference in results depends on the type, intensity, and duration of exercise, as well as the initial health status of individuals and animal species studied.\u003c/p\u003e \u003cp\u003eRegarding ECG results, the increase in PR interval, and reduction in the time of QRS complex in both exercise groups may indicate improvement in cardiac electrical conduction following improving the balance of the autonomic system of the heart and cardiac responses. The reduction in QRS interval can be related to improvement of the ventricular electrical conductivity and reduction of time for impulse propagation and ventricular depolarization. In the blood flow restriction group, a greater reduction in QRS interval compared to pre-exercise levels may reflect the positive effects of blood flow restriction on ventricular conduction velocity. Several human studies that have previously investigated the effects of endurance exercise on ECG, have reported results consistent with our findings (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e) Also in agreement with our findings, an animal study demonstrated that regular endurance exercise programs can enhance cardiac electrical function and reduce arrhythmias in rats with myocardial infarction (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e). However, some studies that contradict our results have shown that intense and prolonged endurance exercise may increase the risk of cardiac arrhythmias in certain individuals (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e). Additionally, it has been shown that intense and prolonged endurance exercise in individuals with underlying heart disease can exacerbate their condition (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e). The discrepancy in these studies' findings appears to be due to differences in exercise intensity and the populations studied.\u003c/p\u003e \u003cp\u003eThe other finding of our study was a reduction in arterial pressure and improvement of heart rate recovery time in both the endurance exercise group with and without blood flow restriction (BFR) in middle-aged individuals with mild hypertension. These results are consistent with the findings of two meta-analyses on the impact of some exercises combined with BFR on cardiovascular health, which reported reductions in blood pressure and improvements in heart rate recovery time (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e). Furthermore, according to the results of another meta-analysis that examined various types of exercises with positive effects on blood pressure, endurance exercise was identified as the most effective type for reducing blood pressure, which aligns with our findings (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e). On the other hand, our results differ from some other research that has highlighted the potential negative effects of intense endurance training. For example, one study warned that high-intensity endurance training could lead to long-term cardiac damage and increase the risk of atrial fibrillation (a type of arrhythmia that can lead to serious heart problems and an increased risk of stroke) in individuals with a history of heart disease (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e). Additionally, another study found that combining resistance training with BFR could increase blood pressure in some individuals with hypertension, which contrasts with the positive findings of the present study (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e). The differences in these results may be attributed to variations in exercise intensity and the type of exercise used in combination with BFR.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThis study demonstrated that ten weeks of mild endurance exercise, as well as endurance exercise combined with blood flow restriction (Ex\u0026thinsp;+\u0026thinsp;BFR), significantly improved heart rate variability (HRV) and ECG parameters in individuals with mild hypertension. Both approaches imposed substantial benefits on HRV indices, ECG parameters, and blood pressure. While both methods were effective, the Ex\u0026thinsp;+\u0026thinsp;BFR approach yielded slightly greater improvements in HRV and certain cardiovascular measures compared to exercise alone. Overall, these findings suggest that combination of blood flow restriction with mild endurance training not only is not harmful but could provide additional benefits for cardiovascular health in comparison with endurance training alone.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"Declarations","content":" \u003cp\u003e \u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e \u003cp\u003e This study was approved by the ethics committee of Kerman University of Medical Sciences (Ethics code: IR.KMU.AH.REC.1402.029), Clinical trial number: IRCT: 20230528058311N1\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent for publication\u003c/strong\u003e \u003cp\u003eNot Applicable\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCompeting Interests\u003c/strong\u003e \u003cp\u003eThe authors declare there is no conflict of interest\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis research is supported by Kerman University of Medical Sciences and Bam University of Medical Sciences\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM.D.Z. contributed to writing the first draft of the manuscript, the initial drafting of the figures, and data collection and analysis.M.N. collaborated in writing and revising the results section, creating the figures, and analyzing the dataS.A. played a role in writing and revising the methods section and supervising the proper implementation of the exercise protocol.M.K. and Kh.M. acted as cardiology specialists in examining and selecting eligible participants for the study.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe want to thank the Kerman University of Medical Sciences for its collaboration.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data will be available on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSessa F, Anna V, Messina G, Cibelli G, Monda V, Marsala G, et al. 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J Cell Mol Med. 2019;23(9):6504\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEngel LE, de Souza FLA, Giometti IC, Okoshi K, Mariano TB, Ferreira NZ, et al. The high-intensity interval training mitigates the cardiac remodeling in spontaneously hypertensive rats. Life Sci. 2022;308:120959.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDavidson BL, Byrne KA, Rood BL, Edwards ES, Akers JD, Wenos DL, et al. Impact of Moderate Exercise Training on Heart Rate Variability in Obese Adults. J Clin Exerc Physiol. 2021;10(1):12\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCastello V, Sim\u0026otilde;es RP, Bassi D, Catai AM, Arena R, Borghi-Silva A. Impact of aerobic exercise training on heart rate variability and functional capacity in obese women after gastric bypass surgery. 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Cardiac behavior and heart rate variability in elderly hypertensive individuals during aerobic exercise: a non-randomized controlled study. Int J Environ Res Public Health. 2023;20(2):1292.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDor-Haim H, Lotan C, Horowitz M, Swissa M. Intensive exercise training improves cardiac electrical stability in myocardial‐infarcted rats. J Am Heart Association. 2017;6(7):e005989.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEijsvogels TM, Thompson PD. Exercise is medicine: at any dose? JAMA. 2015;314(18):1915\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSharma S, Merghani A, Mont L. Exercise and the heart: the good, the bad, and the ugly. Eur Heart J. 2015;36(23):1445\u0026ndash;53.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLavie CJ, Arena R, Swift DL, Johannsen NM, Sui X, Lee D-c, et al. Exercise and the cardiovascular system: clinical science and cardiovascular outcomes. Circul Res. 2015;117(2):207\u0026ndash;19.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWong V, Song JS, Bell ZW, Yamada Y, Spitz RW, Abe T, et al. Blood flow restriction training on resting blood pressure and heart rate: a meta-analysis of the available literature. J Hum Hypertens. 2022;36(8):738\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang T, Tian G, Wang X. Effects of low-load blood flow restriction training on hemodynamic responses and vascular function in older adults: A meta-analysis. Int J Environ Res Public Health. 2022;19(11):6750.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSaco-Ledo G, Valenzuela PL, Ruiz‐Hurtado G, Ruilope LM, Lucia A. Exercise reduces ambulatory blood pressure in patients with hypertension: a systematic review and meta‐analysis of randomized controlled trials. J Am Heart Association. 2020;9(24):e018487.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDomingos E, Polito MD. Blood pressure response between resistance exercise with and without blood flow restriction: A systematic review and meta-analysis. Life Sci. 2018;209:122\u0026ndash;31.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Heart rate variability, endurance exercise training, blood flow restriction, mild hypertension","lastPublishedDoi":"10.21203/rs.3.rs-5347658/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5347658/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground:\u003c/strong\u003e Considering the lack of sufficient information, this study examined the effects of low- intensity endurance exercise training alone and with blood flow restriction (BFR) on blood pressure, electrocardiogram (ECG), and heart rate variability (HRV) in individuals with mild hypertension.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods:\u003c/strong\u003e 43 participants aged 50 – 65 years with mild hypertension were divided into three groups including; endurance exercise with BFR (Ex+ BFR) endurance exercise only (Ex), and a control group (Con) Exercise training was performed three times a week for ten weeks. Before and after the training program, HRV, blood pressure, resting heart rate, and heart rate recovery time were measured and analyzed.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults: \u003c/strong\u003e\u0026nbsp;In both Ex and Ex + BFR groups, RMSSD, SDSD, HF (nu), SD1, and the SD1/SD2 ratio significantly increased but, SD2 and the LF/HF ratio decreased vs. control group. Changes in the aforementioned parameters\u003cstrong\u003e in\u003c/strong\u003e Ex + BFR group than \u003cstrong\u003ein \u003c/strong\u003eEx group.\u003c/p\u003e\n\u003cp\u003eIn comparison to Ex group, Ex + BFR group showed a greater reduction in the QRS interval (15% vs. 12%) and heart rate (7.9% vs. 6.3%) (P \u0026lt; 0.05). Both Ex and Ex+BFR groups experienced a significant decrease in heart rate recovery time and blood pressure (P \u0026lt; 0.001 vs. Con group), with no significant differences between them.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e Low- intensity endurance training combined with blood flow restriction not only had no negative impact on blood pressure, HRV, heart rate recovery, and ECG parameters, but in long term, it may have more positive impact compared to exercise alone in individuals with mild hypertension.\u003c/p\u003e","manuscriptTitle":"Heart rate variability and blood pressure response to low intensity endurance exercise training plus blood flow restriction in individuals with mild hypertension","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-26 13:59:03","doi":"10.21203/rs.3.rs-5347658/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"13f7320e-cc0b-4c04-89ba-8ee0b7bd2a22","owner":[],"postedDate":"November 26th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-12-13T14:38:48+00:00","versionOfRecord":[],"versionCreatedAt":"2024-11-26 13:59:03","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5347658","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5347658","identity":"rs-5347658","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}