Yoga vs. Static Stretching: Recovery Impact on Male Athletes’ Post-HIIT Heart Rate, Respiratory Rate, Blood Pressure, and Heart Rate Variability Analysis

Abstract

Heart rate and heart rate variability indicate an athlete’s cardiovascular recovery and autonomic balance after intense exercise. While stretching aids recovery, its effects on autonomic balance are inconsistent. Yoga’s combination of postures, breathing, and relaxation may further activate the parasympathetic system, making it a promising tool for sports recovery. This study employed a crossover design to examine the effects of yoga and stretching on post 30-min session of high-intensity interval training (HIIT) recovery in male athletes. Twenty athletes of Mae Fah Luang University (Age 20.95±0.99 years old, VO2max 42.53±4.79 ml/kg/min) were given recovery methods, 15-min stretching and 15-min yoga following HIIT. Heart rate, blood pressure, respiratory rate, and heart rate variability were evaluated immediately after HIIT, 5-min, 10- min, 15-min of the recovery period, and at 24-hour after recovery. A Two-way repeated-measures analysis of variance (ANOVA) was employed to examine the interaction effects between different methods and time of recovery. A significance level of 0.05 indicated a statistically significant difference. The findings indicated a statistically significant interaction between the group and time of heart rate variability and respiratory rate (p<0.05, effect size [ES] medium). Post-hoc analysis indicated that performing yoga showed a significantly lower respiratory rate at 5-min, 10-min, and 15-min compared to stretching (p<0.05, ES large). Yoga demonstrated a noteworthy enhancement in heart rate variability during the 5-min and 10-min recovery periods in comparison to stretching. In summary, this study provides empirical evidence supporting the efficacy of yoga as a post-exercise recovery strategy following high-intensity interval training. The role of breathing, rhythmic muscle contractions, and deep relaxation in yoga appears to facilitate the recovery phase more effectively than stretching alone. This suggests incorporating yoga as an active recovery regimen.

Introduction

Post-exercise heart rate recovery (HRR) has emerged as a significant and autonomous indicator for assessing the likelihood of cardiovascular morbidity and death.1 Simultaneous and rapid increase in parasympathetic activity and a gradual reduction in sympathetic activity characterize the immediate cardiovascular response following exercise.2 Additionally, adjustments in heart rate in response to exercise-induced stress likely indicate an individual’s stable autonomic condition.3

The modulation of heart rate variability (HRV) is recognized as a physiological indicator reflecting the state of training readiness and the recovery process.4 Assessing post-exercise heart rate variability (HRV) provides insights into the restoration of physiological homeostasis following intense physical activity. The relationship between the extent and duration of parasympathetic disturbance during the recovery process appears to be associated with exercise factors, such as intensity, duration, and type, as well as individual traits including physical fitness, capacity for recovery and mood state.5 Extensive analyses have been conducted on the temporal progression of parasympathetic recovery to evaluate the responsiveness of the autonomic nervous system and indirectly gauge the overall recovery status of athletes.6

Active cooldowns have been found to expedite the recovery of lactate levels in the bloodstream; however, their effects on muscle tissue regeneration are not necessarily conclusive. Engaging in active cool-downs has the potential to mitigate immune system depression to some extent and facilitate expedited recovery of the cardiovascular and respiratory systems.7 Active cool-down is defined as an activity that involves voluntary participation in low to moderate intensity exercise or movement, performed within one hour of training sessions or competitive events 7. People commonly implement active cool-down to restore the normal functioning of physiological systems after exercise.8 Subsequent research validated these results and proposed that the observed response to active cool-down is indicative of a more rapid recovery of vagal and sympathetic activity.9

Stretching, as an active cool down, has been suggested to facilitate post-exercise recovery, primarily by aiding in the clearance of metabolic waste from skeletal muscles.10,11 Furthermore, stretching may increase parasympathetic activity by enhancing vagal modulation and reducing sympathetic tone12, indicating a restoration of cardiovascular homeostasis, which is an important component of post-exercise recovery.4

Likewise, yoga practices traditionally involve physical postures with stretching, along with additional breathing exercises and deep relaxation.13 Studies on yoga and meditation have demonstrated a significant decrease in stress and anxiety.14 Furthermore, the entire 15-minute period following the intervention consistently observed these beneficial effects on HRV.15 Yoga practices, including supine and inverted postures, stimulate baroreceptor activity, shifting the sympathetic/parasympathetic balance toward parasympathetic dominance, which reduces blood pressure and lowers stress hormone levels.13 Additionally, synchronized breathing and rhythmic muscle contractions, as in yoga, may enhance interoception, further activating the parasympathetic response.16

In a sports context, yoga can be incorporated into pre- and post-workout routines to help athletes prevent injuries and promote recovery.17 However, there is limited evidence on whether yoga benefits recovery in a sports setting.

Examining physiological indicators such as heart rate, heart rate variability, blood pressure, and respiratory rate, which indicate the autonomic nervous system and cardiovascular system’s response to the recovery process. Moreover, there is a claim that yoga training can boost the autonomic nervous system (ANS) and may potentially aid in the recovery phase following HIIT. To our knowledge, however, no research has investigated this speculation. It is important to evaluate and compare the beneficial effects of yoga and stretching as recovery techniques for athletes.

Thus, the objective of this study was to investigate and compare the effects of a 15-minute yoga session and a 15-minute static stretching session on heart rate, heart rate variability, blood pressure, and respiratory rate during the recovery phase of training in male athletes. We hypothesized that the 15-minute yoga session would facilitate the recovery phase after HIIT more effectively than a 15-minute stretching session due to the role of breathing, rhythmic muscle contractions, and deep relaxation involved in yoga.

Methods

Participants

This crossover study employed a robust research design to investigate the impact of two distinct post-high-intensity interval training (HIIT) recovery methods, specifically 15-minute sessions of stretching and yoga, on male athletes from Mae Fah Luang University. A two-way repeated-measures ANOVA was used to look at the interaction effects between the recovery method (yoga vs. stretching) and the time points (before training, right after HIIT, 5,10, and 15 minutes during recovery, and 24 hours after recovery). The rationale for selecting the independent variable (recovery method) is to compare the efficacy of the two commonly used post-exercise recovery techniques. We chose dependent variables such as heart rate, heart rate variability, blood pressure, and respiratory rate based on their relevance in assessing physiological recovery after HIIT.

This study adhered to the principles outlined in the Declaration of Helsinki. The participants provided written consent after being informed of the study and its purpose. The Institutional Review Board of Mae Fah Luang University approved all studies. This research was carried out fully in accordance to the ethical standards of the International Journal of Exercise Science.18

The study’s inclusion criteria were male athletes within the age range of 18 to 25 years, with a VO2max ranging from 35 to 45 ml/kg/min, a BMI equal to or less than 25 kg/m², a consistent training regimen of at least 60 minutes per session, three times per week for the previous three months, and meeting the requirements outlined in the Physical Activity Readiness Questionnaire (PAR-Q).

Participants with orthopedic, neurological, or pain-related conditions, or those who had received medical or physical therapy, were excluded from the study. Participants with prior yoga experience were also excluded to reduce bias and ensure that any observed effects could be attributed solely to the yoga intervention rather than familiarity with the practice.

Participants were instructed to refrain from engaging in strenuous physical activity for 24 hours and to avoid consuming alcohol prior to the start of the experiment.

The participants were twenty athletes from the football club at Mae Fah Luang University, Chiang Rai, Thailand, with an average age of 20.95±0.99 years, VO2max of 42.53±4.79 ml/kg/min, and BMI of 23.30±2.14 kg/m².

Protocol

Twenty individuals who met the inclusion criteria were selected to participate in this crossover study. The study participant allocation and analysis are displayed in Figure 1.

Figure 1.

The study participant allocation and analysis.

Participants performed treadmill running according to the prescribed high-intensity interval training (HIIT) protocol. Following this, they underwent a 15-minute session of static stretching for the SS trial and a 15-minute session of yoga for the YG trial. We instructed participants to refrain from engaging in strenuous physical activity during the designated 5-day washout period.

The HIIT session19 consisted of a 2-minute warm-up (walking at 6 km/h, grade 0%), followed by a high-intensity interval session: 12 sets of 1-minute running at 85% of maximum heart rate, interspersed with 1 min of walking at 50% of maximum heart rate. The session concluded with a 3-minute cool-down (walking at 6 km/h, grade 0%). The training load was quantified using the Zephyr Bioharness™ and RPE scales20 and the subsequent recovery phase.

For the yoga session, participants were instructed to perform yoga postures for 15 minutes by a certified yoga instructor. The session began with a 2-min of breathing practice for relaxation. This was followed by a 10-min intervention involving a child pose, downward-facing dog pose, half-reclined hero, lateral arch pose, warrior I pose, and head-to-knee forward, 50 s for each posture × 2 sessions. The session ended with a 3-min corpse pose.

For the stretching session, following the ACSM’s recommendation21, participants were instructed to engage in a fifteen-minute stretching session. The session commenced with a 2- minute resting period, followed by a 10-minute stretching routine, targeted specific muscles group for HIIT, involving the latissimus dorsi stretch, calf stretch, quadriceps stretch, side stretch, hip flexor stretch, and hamstring stretch. Each stretch was held for 50 s and repeated twice. The session was concluded with a 3-minute rest period.

We collected data at multiple time points: before HIIT session (T1), immediately after HIIT (T2), 5 min (T3), 10 min (T4), 15 min (T5) during the recovery period following HIIT session, and one day after recovery (post-24 h, T6). This study used Zephyr Bioharness ™ to monitor the heart rate, heart rate variability, and respiratory rate. Previous findings support the Zephyr Bioharness™ as a reliable tool (correlation coefficients of 0.85–0.98) and a valid one (0.74–0.99 compared to gold standards) for monitoring various physiological parameters across diverse contexts.22

For heart rate variability, we measured the standard deviation of the interbeat intervals (IBI) of normal sinus beats, known as SDNN (ms). The greater impact on SDNN indicates increased parasympathetic activity 23. In addition, we used a blood pressure monitor (Omron HEM7120) to monitor blood pressure.

Statistical Analysis

To test the primary hypothesis of sample size determination 24 this experimental study estimated the sample size based on a previous study25 with an effect size of 0.46, alpha level of 0.05, and beta of 0.02; therefore, there were 20 participants in each group.

We performed all statistical analyses using IBM SPSS statistics version 26 (IBM Corporation, Armonk, NY, USA). We tested the distribution of all data using Shapiro-Wilk tests, and we found it suitable for parametric testing. Two-way Analysis of Variance (Two-way ANOVA) test with post hoc pairwise comparison was performed to assess the interactions effect of group-time. If significant interactions were seen, Repeated Measures Analysis of Variance (RM ANOVA) test was performed to determine if differences exist between the 6 times within each trial. Partial eta squared (ηp²) was used to represent the effect size (<0.06 = small, 0.06–0.14 = medium, ≥0.14 = large).26 Statistical significance was set at p < 0.05, and Bonferroni correction was used for multiple comparisons.

Twenty participants were tested for heart rate, heart rate variability, respiratory rate, and blood pressure. The assessments were conducted by the same evaluator in two separate trials, with a time interval of five days between each trial.

Results

The effects of 15-min yoga (YG) and 15-min static stretching (SS) on post-training heart rate (HR), SDNN, respiratory rate (RR), and blood pressure (BP) recovery in male athletes are shown in Table 1. and Figure 2. Two-way repeated measures were conducted to examine the effects of time and intervention on the HR, SDNN, RR, and BP during post training recovery. There was a statistically significant interaction between the effects of time and intervention on SDNN, F (5, 190) = 3.751, p = .003, ηp² = .090 and RR, F (5, 190) = 8.825, p = .000, ηp² =.188 respectively. Post-hoc Bonferroni analysis revealed that the yoga group (YG) led to a quicker recovery of parasympathetic activity compared to static stretching (SS), with a lower RR at T3, T4, and T5 of recovery (p < 0.05), as well as improved SDNN at T3 and 10-min T4 of recovery compared to SS (p < 0.05).

Table 1.

Mean ± SD of heart rate, SDNN, respiratory rate and blood pressure post HIIT following 15-min yoga and 15-min static stretching in male athletes.

Variables	Trial	Time points						p value
		T1	T2	T3	T4	T5	T6
HR	YG	70.90±199	123.25±4.41	104.10±2.78	114.25±2.77	92.65±3.65	67.20±1.84	>.05
	SS	77.70±1.95	129.50±3.34	110.25±3.20	116.85±3.23	84.25±2.69	72.70±1.90
SDNN	YG	82.25±6.74	25.40±3.63	44.80±4.95	35.40±3.59	60.20±8.28	77.70±7.11	.00*
	SS	76.40±5.85	21.20±2.77	19.45±2.05	19.95±2.07	48.20±5.92	63.20±4.07
RR	YG	16.80±0.63	25.50±1.29	14.00±0.91	15.30±0.95	8.95±0.88	15.30±1.05	.00*
	SS	15.85±0.96	28.55±1.13	20.30±0.93	20.25±1.09	17.50±0.77	16.30±0.61
SBP	YG	127.05±10.99	131.15±15.97	134.60±17.62	119.20±14.24	121.90±11.18	122.50±15.82	>.05
	SS	129.70±11.37	135.30±14.82	134.95±18.04	123.40±20.13	130.05±14.73	122.85±13.43
DBP	YG	74.80±12.75	78.45±11.71	81.80±10.70	76.45±23.95	70.95±10.27	75.10±11.63	>.05
	SS	77.55±10.49	80.50±12.98	89.90±22.07	74.05±16.71	75.95±12.41	72.60±14.54

^*p < 0.050.

p value of main effect of time × group interaction tested by two-way repeated-measures analysis of variance (ANOVA). HR = Heart Rate; SDNN = Standard Deviation of the interbeat intervals of normal sinus beats; RR = Respiratory Rate; SBP = Systolic Blood Pressure; Diastolic Blood Pressure; YG = Yoga Trial; SS = Static Stretching Trial; SD = standard deviation; T1 = before HIIT session; T2 = immediately after HIIT; T3 = 5-min after HIIT; T4 = 10-min after HIIT; T5 = 15-min after HIIT; T6 = 24 h after HIIT.

Figure 2.

Change in SDNN (2a), respiratory rate (2b), heart rate (2c), diastolic blood pressure (2d), and systolic blood pressure (2e) of post HIIT after 15-min yoga compared to15-min stretching session. (mean ± SD). Data were collected at multiple time points: before HIIT session (T1), immediately after HIIT (T2), 5 min after HIIT (T3), 10 min after HIIT (T4), 15 min after HIIT (T5) throughout the recovery period, and one day after recovery (post-24 h, T6). Asterisk (*) indicates significant difference between trials. Number sign (#) indicates significant difference with T1. Alpha (α) significant indicates difference with T2. Statistical significance is set at p < .05.

For within group comparison using RM ANOVA for both YG and SS demonstrated the similar trend of changed for SDNN and RR (see figure 2a and 2b). RM ANOVA determined that mean SDNN (ms) differed statistically significantly between time points for YG trial (F(5, 95) =28.852, p=.000, ηp2=.608), and for SS trial (F(5, 95) =50.239, p=.000, ηp2=.726). In the same way, RM ANOVA determined that mean RR (times/min) differed statistically significantly between time points for YG trial (F(5, 95) =37.859, p=.000, ηp2=.666), and for SS trial (F(5, 95) =35.787, p=.000, ηp2=.653).

Post hoc analysis revealed that SDNN significantly decreased, and RR significantly increased from before HIIT (T1) to the recovery period at various time points (e.g., T2, T3, T4) (see figure 2a and 2b) indicating that HIIT stimulated sympathetic activity in both YG and SS groups. During the recovery period, post hoc analysis also showed that SDNN significantly improved, and RR significantly decreased from post-HIIT (T2) to various recovery time points (e.g., T3, T5) (see figure 2a and 2b) further indicating that both YG and SS groups facilitated parasympathetic activity during recovery.

For YG, post hoc revealed that SDNN (see figure 2a) was statistically significantly decreased from T1 to T2 (95% CI, 32.251 to 69.749, p=.000), T1 to T3 (95% CI, 13.057 to 50.143, p=.000), T1 to T4 (95% CI, 21.257 to 60.743, p=.000), and T3 to T4 (95% CI, .217 to 18.583), p=.042). Besides, SDNN was statistically significantly improved from T2 to T3 (95% CI, 32.523 to −6.268, p=.001), T2 to T5 (95% CI, −59.082 to −10.518, p=.002), T2 to T6 (95% CI, −71.258 to −33.342, p=.000), T3 to T6 (95% CI, −53.658 to −12.142, p=.001), T4 to T5 (95% CI, −48.225 to −1.375, p=.032), and T4 to T6 (95% CI, −66.526 to −18.074, p=.000).

Furthermore, post hoc revealed that RR of YG was statistically significantly increased from T1 to T2 (95% CI, −13.61 to −3.79, p=.000), and T5 to T6 (95% CI, −9.785 to −2.915, p=.000). In addition, RR (see figure 2b) was statistically significantly decreased from T1 to T5 (95% CI, −13.61 to −3.79, p=.000), T2 to T3 (95% CI, 6.133 to 16.867, p=.000), T2 to T4 (95% CI, 5.064 to 15.336, p=.000), T2 to T5 (95% CI, 12.283 to 20.817, p=.000), T2 to T6 (95% CI, 4.207 to 16.193, p=.000), T3 to T5 (95% CI, 1.453 to 8.647), p=.002), and T4 to T5 (95% CI, 3.156 to 9.544, p=.000).

For SS, post hoc revealed that SDNN (see figure 2a) was statistically significantly decreased from T1 to T2 (95% CI, 37.821 to 84.279, p=.000), T1 to T3 (95% CI, 40.384 to 85.216, p=.000), from T1 to T4 (95% CI, 39.006 to 85.594, p=.000), T1 to T5 (95% CI, 10.165 to 57.935, p=.002). Additionally, SDNN was statistically significantly improved from T2 to T5 (95% CI, −44.220 to −9.870, p=.001), T2 to T6 (95% CI, −57.788 to −26.212, p=.000), T3 to T5 (95% CI, −42.694 to −14.806, p=.000), T3 to T6 (95% CI, −58.511 to −28.989, p=.000), T4 to T5 (95% CI, −43.001 to −13.499, p=.000), and T4 to T6 (95% CI, −58.049 to −28.451, p=.000).

Likewise, post hoc revealed that RR of SS (see figure 2b) was statistically significantly increased from T1 to T2 (95% CI, 17.481 to −7.919, p=.000), and T1 to T3 (95% CI, −8.703 to −.197, p=.035). RR was also statistically significantly decreased from T2 to T3 (95% CI, 5.331 to 11.169, p=.000), T2 to T4 (95% CI, 3.994 to 12.606, p=.000), T2 to T5 (95% CI, 7.23 to 14.87, p=.000), T2 to T6 (95% CI, 8.282 to 16.218, p=.000), T3 to T6 (95% CI, .465 to 7.535, p=.018), and T4 to T6 (95% CI, .868 to 7.23, p=.006).

However, there was no statistically significant interaction between the effects of time and intervention on HR recovery, F (5, 190) = .471, p = .797, ηp² = .012, systolic blood pressure (SBP), F (5, 190) = .686, p = .635, ηp² = .018, diastolic blood pressure (DBP), F (5, 190) = 1.119, p = .352, ηp² = .029. The changed in HR, SBP, DBP post HIIT following YG and SS were showed in Table 1 and figure 2c, 2d, 2e respectively.

Discussion

The main result of this study was that both yoga and stretching provided sufficient physiological stimulation to alter autonomic regulation and improve parasympathetic reactivation after exercise. Furthermore, research findings indicated that the practice of yoga for recovery purposes exhibited a notably greater impact on parasympathetic activity than stretching as a recovery method.

Research has shown that there is a decrease in parasympathetic nerve activity following acute activities such as resistance training27, endurance exercise28, and high-intensity interval training. 29 The findings of this study confirm that yoga practice can augment parasympathetic activity during the period following exercise-induced stress. Previous studies have shown that a single yoga session, which includes stretching exercises, breath control, and meditation30, activates the cardiac autonomic nervous system, specifically the parasympathetic nervous system.31 Moreover, after practicing 90-min yoga stretching for 60 and 120 min, the heart rate variability (i.e., RMSSD and Ln HF) increased and potentially augmented the parasympathetic nerve activity 31. Accordingly, the authors proposed that the practice of yoga stretching may potentially augment parasympathetic nerve activity.31

Yoga has the potential to influence cardiac autonomic control.32 Uncertainty surrounds the precise manner in which yoga affects autonomic activity; however, certain yoga practices directly activate the vagus nerve and augment parasympathetic output.33 This leads to a state of parasympathetic control, resulting in improved cardiac function, mood, and energy levels, as well as enhanced neuroendocrine, metabolic, cognitive, and immune responses.34,35 Furthermore, Yoga practices, including supine and inverted postures, stimulate baroreceptor activity, shifting the sympathetic/parasympathetic balance toward parasympathetic dominance, which reduces blood pressure and lowers stress hormone levels 13. In addition, studies have reported that yoga breathing practices significantly influence heart rate variability (HRV) and respiratory sinus arrhythmia (RSA), both of which are highly susceptible to changes in breathing rate. Previous research has indicated that engaging in yoga-style (Kapalabhati) breathing exercises can lead to a decrease in vagal activity, as evaluated in either the frequency or time domain of HRV. These decreases in vagal activity have been observed to persist even after the practice has ended.36 Additionally, synchronized breathing and rhythmic muscle contractions, as practiced in yoga, may enhance interoception, thereby further activating the parasympathetic response.16 This mechanism can be explained by the polyvagal theory proposed by Stephen Porges, which hypothesizes that autonomic regulation is achievable through interoception (i.e., awareness of the internal state of the body’s systems) and self-regulatory skills.37,38

In addition, the present study demonstrated that static stretching during the recovery period resulted in a notable enhancement of parasympathetic activity. Nevertheless, improvements in respiratory rate and SDNN were comparatively lower in yoga recovery. It has been suggested that static stretching could potentially enhance parasympathetic activity12, hence facilitating the prompt recovery of Ln-rMSSD following static stretching.10

According to Wong and Figueroa12, it has been observed that acute static stretching exercise has the potential to enhance parasympathetic nerve activity. According to a prior investigation conducted by Wong and Figueroa12, the impact of stretching exercise on heart rate variability (HRV) can be attributed to three probable processes. These mechanisms include enhanced baroreflex sensitivity, a physiological relaxation response, and an elevation in nitric oxide levels. In the context of acute stretching exercise, it has been hypothesized that the relaxation response, which encompasses both psychological and physical aspects, plays a significant role in augmenting parasympathetic nervous system activity.12,31,39

Thus, while stretching facilitates the recovery process by enhancing baroreflex function and promoting relaxation, we propose that the breathing patterns, rhythmic muscle contractions, and deep relaxation in yoga are the primary mechanisms that lead to greater facilitation of the recovery phase compared to stretching.

In conclusion, this study represents the inaugural investigation into the impact of yoga on post-exercise recovery, as well as the consideration of yoga as a potential method for post-exercise recovery. Yoga practice was associated with a decrease in the respiratory rate during recovery, suggesting a potential augmentation of parasympathetic activity. However, both yoga and stretching have emerged as viable post-exercise recovery methods, with similar trends observed in heart rate reduction during recovery. Additionally, the recovery period after yoga activity was associated with lower blood pressure levels.

The present study has certain limitations. This study did not include active control trials, such as walking or sitting. Moreover, uncontrolled confounding variables, including psychological factors affecting recovery, unfamiliarity with yoga, and familiarity with stretching, present a limitation in this study. Increasing the sample size is critical to enhancing the study’s effect size Nevertheless, this study provides initial evidence of the potential efficacy of yoga in facilitating post-exercise recovery. Therefore, we recommend future research to compare the impact of yoga on recovery with alternative active recovery modalities such as walking and passive recovery modalities like sitting and passive stretching.

The findings suggest that incorporating holistic approaches like yoga into post-exercise recovery regimens may offer significant clinical benefits. The observed physiological effects, including enhanced parasympathetic activity and reduced blood pressure, highlight the potential of yoga in supporting overall recovery, promoting relaxation, and improving cardiovascular health.

This could be particularly valuable for athletes or individuals engaging in intense physical activity, as it provides an alternative or complementary method to traditional recovery practices.

Future research should explore the long-term effects of these interventions on athletic performance, injury prevention, and overall cardiovascular health.