Impact of Spinal Flexion and Extension-based Yoga Postures on Autonomic Nervous System Activity in Moderately Experienced Yoga Practitioners: A Randomized Crossover Trial

Abstract

Background:

The autonomic nervous system (ANS) is a complex neural network responsible for maintaining homeostasis through its sympathetic and parasympathetic components. Yoga, an ancient mind–body practice, has been shown to modulate autonomic function, promoting homeostasis. This study aims to comprehensively evaluate the differential impact of spinal flexion and extension-based yoga postures on autonomic modulation in practitioners with at least 2 years of consistent yoga practice.

Methods:

This randomized crossover trial included 40 participants of both genders who had practiced yoga for at least 2 years, averaging 3–5 sessions per week. Participants were randomly allocated (1:1) into two groups: Group 1 (n = 20) practiced a set of three spinal flexion-based postures (SFP: Halasana, Padahastasana, Shashankasana) on day 1 and three spinal extension-based postures (SEP: Ardhachakrasana, Ushtrasana, Chakrasana) on day 2; Group 2 (N = 20) practiced SEP on day 1 and SFP on day 2. Autonomic function was assessed using heart rate variability (HRV), respiratory rate (RR), galvanic skin resistance (GSR), and electrogastrogram (EGG), which were measured for 5 min at baseline and 5 min postintervention on both days. The data were analyzed based on linear mixed models.

Results:

Both SFP and SEP interventions resulted in a significant increase in the high-frequency (HF) component of HRV (P < 0.001), indicating parasympathetic predominance immediately postintervention. RR showed a significant increase postintervention (P < 0.001), likely due to the higher energy demands of the postures. No significant changes were observed in GSR for either intervention. EGG recordings indicated a nonsignificant decrease in overall gastric motility postintervention, potentially due to vagal nerve stimulation.

Conclusion:

Both spinal flexion and extension-based yoga postures enhance parasympathetic activity in moderately experienced practitioners, as evidenced by increased HF HRV. Future research should focus on long-term impact of different yoga postures and employ advanced measurement techniques for greater methodological rigor.

Introduction

The autonomic nervous system (ANS) is a complex neural network that comprises of sympathetic nervous system, parasympathetic nervous system, and enteric nervous system. It innervates most parts of the human body and is majorly responsible for maintaining homeostasis and orchestrating the allostatic response – the body’s adaptive mechanisms to physiological or psychological stressors.[1] The afferent pathways of the ANS carry sensory information from various parts of the body to the control centers in the hypothalamus and the brainstem. The efferent pathways of ANS are largely mediated by autonomic reflexes and consist of two neurons: a preganglionic neuron that originates in the central nervous system (CNS) and synapses with a postganglionic neuron that terminates at the target organ. The ANS has two anatomically and functionally distinct components which are the sympathetic nerves with short cholinergic preganglionic fibers and long adrenergic postganglionic fibers and the parasympathetic nerves with long cholinergic preganglionic fibers and short cholinergic postganglionic fibers.[2] Each of these distinct systems differentially respond to different situations, with the overall function of the ANS being to maintain homeostasis.[3]

Yoga is a mind–body practice with its origins being traced back to Indian scriptures from over 5000 years ago. One such ancient Indian scripture, the Bhagavad Gita describes yoga as “samatvam yoga ucyate” which translates to yoga is equanimity or in other words homeostasis.[4] This hypothesis is supported by the large body of scientific evidence which has demonstrated the autonomic modulation effect of yoga practice.[5,6,7] One study that compared the differential autonomic response between novice yoga practitioners and advanced yoga practitioners found that yoga leads to autonomic normalization in both groups further solidifying the hypothesis that yoga helps achieve homeostasis.[8]

Spinal flexion and extension-based yoga postures were specifically chosen for this study due to their potential to differentially stimulate autonomic pathways through mechanical, neural, and respiratory mechanisms. Spinal flexion (forward bending) postures stretch the craniosacral region of the spine, affecting the sympathetic nerve fibers located along this axis. Studies suggest that such stretching may decrease the axon diameter of sympathetic fibers, potentially reducing conduction velocity, which has been associated with sympathetic activation.[9] Supporting this, research has observed heightened sympathetic activity in individuals with idiopathic scoliosis, underscoring the link between forward spine bending and sympathetic nervous system activation.[10,11]

In contrast, spinal extension (backward bending) postures involve chest expansion and slow, deep abdominal breathing. These actions are known to enhance vagus nerve activity by improving arterial baroreceptor sensitivity, leading to parasympathetic predominance.[12,13] While sympathetic arousal during spinal flexion may temporarily disturb autonomic balance, spinal extension postures may promote parasympathetic dominance, leading to relaxation and restoring autonomic equilibrium.

Most yoga studies that aimed to assess autonomic function have done so by measuring cardiac autonomic activity through heart rate variability (HRV).[14] However, many other physiological measurements are influenced by the ANS, due to its neural control over most of the human body.[15] To comprehensively understand the autonomic response to spinal flexion versus spinal extension-based yoga postures, in the current study, we included HRV, respiratory rate (RR), galvanic skin resistance, and electrogastrogram as primary outcome variables. Despite the potential of these measures, there is a notable gap in studies enumerating the differential autonomic responses to specific yogic stimuli. For example, while yoga’s general effects on HRV are well-documented, the specific autonomic responses elicited by distinct postures remain underexplored.

The current study aims to address this gap by exploring the differential impact of spinal flexion versus spinal extension-based yoga postures on autonomic modulation in healthy, moderately experienced yoga practitioners (defined as individuals with at least 2 years of regular yoga practice). We hypothesize that spinal flexion-based postures will predominantly activate sympathetic activity, while spinal extension-based postures will enhance parasympathetic activity, providing valuable insights into their potential therapeutic applications.

Methods

Trial design

The current study was a single-center, open label, randomized crossover trial, conducted between November 2022 and December 2023. The trial tested two interventions (spinal flexion-based postures and spinal extension-based postures) over two time periods of 3 h each with a washout period of 24 h between them. Some of the known disadvantages of the crossover design like larger dropout rate and a potential carryover effect were not expected in this intervention, and hence, a crossover design was chosen. It was designed and reported in accordance with CONSORT 2010 statement: extension to randomized crossover trials.[16]

Participants were recruited from a college of naturopathy and yogic sciences in South India, targeting a population of residential yoga students. Recruitment was conducted using visually appealing flyers displayed on campus notice boards, which included details about the study purpose, eligibility criteria, and contact information. The response rate to the advertisements was approximately 43.2%, with interested students contacting the research team to express interest.

Students who responded to adverts were assessed for eligibility using a predesigned form. Those who met the inclusion criteria were randomly assigned to one of two groups labeled Group 1 and Group 2. On the 1^st day, Group 1 practiced Intervention B consisting of three spinal flexion-based postures (SFP), while the other group was asked to practice Intervention A: three spinal extension-based postures (SEP). After a washout period of 24 h, on day 2, the order was reversed, with those who practiced SFP on day 1 moving to SEP intervention and the other group continuing with SFP intervention. The participant flow is described in Figure 1.

Figure 1.

Consort flow diagram. SFP = Spinal flexion-based postures, SEP = Spinal extension-based postures, EGG = Electrogastrogram, HRV = Heart rate variability, GSR = Galvanic skin resistance, RR = Respiratory rate

Eligibility criteria

The inclusion criteria for the study were as follows: participants aged between 20 and 25 years, of both genders, with a minimum of 2 years of experience in practicing postures (averaging 3–5 sessions per week) involving spinal flexion and extension. Only healthy volunteers willing to participate were considered eligible.

The exclusion criteria eliminated individuals with any metabolic diseases, a history of spinal injury within the past 6 months, or <75% efficiency in reaching the final posture. Female participants during their menstrual cycle and those under routine medication were also excluded from the study.

Ethical considerations

The principal investigator obtained a written and signed informed consent form from each participant, expressing their agreement to participate, before recruiting them for the study. In addition, they received verbal and written information regarding the study and plenty of opportunities to ask any questions. Participants were allowed to withdraw their consent at any point of time. The trial was registered under Clinical Trials Registry of India CTRI (CTRI/2022/11/047454), and institutional ethics committee approval was obtained vide letter no (RES/IEC-SVYASA/253/2022) from IEC of S-VYASA University.

Intervention

The intervention A consisted of a set of three backward bending postures which involve spinal extension and Intervention B consisted of three forward bending postures involving spinal flexion. The intervention was administered at the same time, between 7 am and 10 am for every participant to account for diurnal variation in autonomic variables. The participants were informed in prior about the postures to be performed, and during the study, instructions for each posture were given by a trained yoga physician. For each posture, a maximum duration of 15 s was allowed to reach the final posture and was then maintained for 3 min as a static pose. They were then allowed 15 s to release the posture and return to neutral position. The instructor ensured to advice participants to synchronize their breathing with body movements both while reaching the final posture and releasing it. During the 3 min of maintenance as a static pose, participants were asked to keep breathing normally, hold the pose with stability, and comfort without overstraining [Figure 2].

Figure 2.

Intervention. SFP = Spinal flexion-based postures, SEP = Spinal extension-based postures

Adherence to prescribed yoga postures was monitored by real-time observation throughout the study by the instructor. Any deviation from the prescribed posture was recorded and categorized according to severity (minor, moderate, and severe). The adherence rate was calculated by dividing the number of times the posture was correctly executed by the total number of attempts.

Intervention A: Spinal extension-based postures

Ardhachakrasana (half wheel pose)

The participants were asked to stand straight with their legs together and hands by the side of their body. Then, they were asked to place their hands on their waist and bring their elbows as close to each other as possible. As they inhale, they were asked to bend back from the lower back and maintain in this final pose with normal breathing and awareness on the back stretching.

Ushtrasana (camel pose)

The participants were asked to sit on their heels, with their legs folded at the knees, keeping their back and neck erect and place their palms on the knees. They were then asked to come up to kneel down posture, and as they inhale place their right hand on the right heel and left hand on the left heel, pushing their pelvis slightly forward. They were asked to maintain in this final pose with normal breathing and awareness on the back stretching.

Chakrasana (wheel pose)

The participants were asked to lie down on their back, with their legs together and hands by the side of the body. They were asked to bend their legs at the knees, place their palms on the ground beside the ears, with fingers pointing forward. As they inhale, they were asked to push the ground with their palms and feet, and raise their head, chest, and pelvis from the ground, maintain the whole-body weight only on the palms and feet. They were asked to maintain in this final pose with normal breathing and awareness on the back stretching.

Intervention B: Spinal flexion-based postures

Halasana (plough pose)

The participants were asked to lie down on their back, with their legs together and hands by the side of the body. Then, as they inhale, they had to raise their legs up to 90°, press down on the arms and lift the buttocks, rolling the back away from the floor. They had to lower the legs over the head trying to touch the toes to the floor behind the head. They were then asked to turn the palms up, bend the elbows and place the hands behind the ribcage to support the back. Relax and hold the final pose with normal breathing.

Padahastana (hand to foot pose)

The participants were asked to stand with the spine erect, feet together and hands beside the body. Distribute the weight of the body evenly on both feet. Slowly bend forward, first bending the head, taking the chin towards the chest, then bending the upper trunk, the mid-trunk and finally the lower trunk. Place the palms on the floor beside the feet.

Shashankasana (hare pose)

The participants were asked to sit on their heels, with their legs folded at the knees, keeping their back and neck erect and place their palms on the knees. They were then asked to raise their hands above their head, keeping the elbows straight and then bend forward from the lower back until their forehead touches the ground. They were asked to maintain the posture with normal breathing.

Outcomes

All the assessments were performed by the same physician, and at the same time everyday between 7 am and 9 am. Assessments were done in a dimly lit, sound attenuated room. Participants were asked to lie down in supine position, and during recordings, they were instructed to close their eyes and maintain normal breathing.

The baseline assessments were taken for 5 min before the intervention, and postassessments were conducted immediately after the postures were performed for 5 min. An 8 channel fully integrated data acquisition system Power lab 8/35 from AD instruments, Australia, was used for simultaneous recording of electrocardiogram (ECG), RR, galvanic skin resistance (GSR), and electrogastrogram (EGG). Lab Chart 8 software was used to extract the data offline.

Heart rate variability

The ECG was recorded using standard limb lead II configuration by placing disposable AgCl gel electrodes on the right arm (palmar surface of the hand above the wrist joint), left leg (inner surface of the leg above the ankle joint), and the ground electrode on the right leg (inner surface of the leg above the ankle joint). The data were acquired at a sampling rate of 1024 Hz. The HRV was derived from noise-free ECG data excluding ectopic beats, by computing the successive normal-to-normal intervals, and spectral analysis was done by Fast Fourier transformation.

Respiratory rate

The RR was recorded by attaching a respiratory effort transducer approximately 8 cm above the lower costal margin. Care was taken to tighten the transducer in a manner that did not impede full inspiration. The RR was derived as the number of breath cycles per minute after averaging it across the 5 min by computing successive inspiratory and expiratory cycles.

Galvanic skin resistance

The skin resistance was recorded by firmly attaching bipolar metal electrodes with straps to the palmar surface of the middle segments (phalanges) of the index and middle fingers of one hand. The signals were digitized using the Power Lab system at 1 kHz with 12-bit resolution. The GSR data was extracted from the electrodermal response recorded in kilo Ohms, averaged across 5 min with data taken every 30 s.

Electrogastrogram

EGG was used to assess the gastric myoelectric activity, using a configuration for 1-channel EGG by placing one electrode at the midpoint on a line connecting the xiphoid and umbilicus, and the other electrode 5 cm away, up and 45° to the subject’s left. The ground electrode was placed on the right costal margin, horizontal to the first active electrode. The EGG was recorded with a predefined amplitude range of 50–400 μV and a frequency range of 0.5–9.0 cpm (0.008–0.15 Hz). The EGG parameters that were extracted from the spectral analysis included dominant frequency and power, percentage of normal gastric slow waves, and percentage of power distribution.

Sample size

The sample size was estimated using G*Power version 3.1.9.7 (Developed by Erdfelder, Faul, Buchner [1996], Universität Düsseldorf, Germany). Based on prior literature evaluating autonomic responses to yoga interventions, an expected effect size of 0.62 was derived from the study by Bhavanani et al., which compared the immediate effects of different yoga asanas on heart rate (HR) and blood pressure in healthy young volunteers.[17] Using a within-subject standard deviation (σ) of 1, a power of 80% (Z = 0.84), and a significance level of 0.05 (Z = 1.96), the total sample size required was 40. Since this trial assessed the immediate effects of the intervention and required participants to visit the lab for a short duration of only 2 days, minimal dropouts were anticipated. Therefore, 40 participants were recruited.

Randomization

The randomization was done by a technician off-site not involved in participant recruitment and assessments, using a computer-based software that generated the group allocation scheme, thereby concealing the intervention allocation. The stratification factor used in the randomization included gender, with an equal number of male and female participants in each group. Just before data collection, the principal investigator telephoned the technician and obtained the group allocation of the participant.[18]

Safety measures

The study was conducted in a safe environment, ensuring that the participants wore appropriate and comfortable clothing and provided anti-skid yoga mats. It was supervised by a trained yoga physician who counseled the participants on the right way to attain final postures and maintain them with stability, to avoid falls or injuries.

A systematic monitoring process was implemented to ensure participant safety. A specific register was maintained to record any adverse events, defined as any unexpected physical discomfort, pain, or injuries arising during or after the session. The register was regularly reviewed and submitted to the institutional ethics committee to ensure compliance with ethical standards and transparency. The research team ensured the availability of medical staff and a facility equipped to handle emergencies. Participants were encouraged to report any adverse sensations or issues immediately during or after the session. Throughout the trial, no adverse events were reported, affirming the safety of the interventions under the supervised study conditions.

Statistical analysis

The demographic data for categorical variables are expressed as mean and standard deviation and for continuous variables as frequency of observations and percentages.

This study aimed to evaluate the effects of two different interventions SFP and SEP on autonomic function in healthy volunteers, administered over two time periods of 3 h each with a washout period of 24 h in between. A linear mixed effects model was used to analyze the data accounting for the repeated measures and crossover design. The model included fixed effects for intervention, time point and sequence, as well as a random intercept for participants. The analysis for outcomes was done based on intention-to-treat principle. Imputation for missing values was not done as linear mixed model already accounts for missing values. All data were analyzed using the Jamovi project (2022). Jamovi (version 2.3).

Results

A total of 40 participants of mean age 21.92 ± 1.69 completed the trial. They were all moderately experienced yoga practitioners with an average of 4.57 ± 1.67 years of experience and practicing 4.87 ± 0.45 h per week [Table 1].

Table 1.

Demographic characteristics and baseline data of the participants

Variable		Value
Age		21.92±1.69
Gender
Male		50
Female		50
BMI		21.42±1.86
Number of years of yoga experience		4.57±1.67
Number of hours of yoga practice per week		4.87±0.45
Baseline data
Resting heart rate		75.89±10.59
RR		15.24±4.27
Systolic blood pressure		104.31±8.81
Diastolic blood pressure		70.22±5.70

Values are mean±SD or n (%). BMI: Body mass index, SD: Standard deviation, RR: Respiratory rate

The adherence rate to posture execution was 85% across all participants, with minor deviations observed in 12% of sessions and moderate deviations in 3%. No significant differences in adherence rates were observed between the intervention and control groups (P = 0.42).

Among the time domain parameters of HRV, average time interval between normal-to-normal intervals (average NN), standard deviation of NN intervals (SDNN), The root mean square of the mean of the sum of the squares of differences between adjacent NN intervals (RMSSD), and Percentage of the number of pairs of adjacent NN interval difference by >50 ms (pNN50) showed a slight increase following the SFP intervention compared to the SEP intervention. Conversely, the average HR exhibited a decrease after the SFP intervention compared to SEP. However, these changes were not statistically significant.

Intraintervention comparisons of frequency domain parameters revealed a statistically significant increase in high-frequency (HF) (P < 0.05) after both interventions. Nevertheless, comparisons between the two interventions indicated no significant difference.

Similarly, RR significantly increased (P < 0.05) after both interventions in intra-intervention comparisons. However, no significant difference was observed when comparing the two interventions.

GSR decreased after the SFP intervention and increased after the SEP intervention, although these changes were statistically nonsignificant [Table 2].

Table 2.

Changes in heart rate variability, respiratory rate, galvanic skin resistance

Variable		SFP								SEP
		Pre		95% CI		Post		95% CI		Pre		95% CI		Post		95% CI
Average NN		834 (20.9)		793–876		884 (21.1)		842–926		822 (21.3)		779–864		839 (21.3)		797–882
SDNN		56.3 (3.57)		49.3–63.4		63.6 (3.61)		56.4–70.7		60.2 (3.65)		52.9–67.4		62.2 (3.65)		55.0–69.4
Average HR		73.7 (1.69)		70.5–77.2		69.6 (1.71)		66.3–73.0		74.9 (1.73)		71.5–78.3		73.5 (1.73)		70.1–76.9
RMSSD		48.7 (4.44)		39.9–57.5		58.0 (4.49)		49.1–66.9		51.4 (4.54)		42.4–60.4		57.0 (4.54)		48.0–66.0
pNN50		25.7 (3.33)		19.1–32.3		33.4 (3.36)		26.8–40.1		26.7 (3.40)		19.9–33.4		33.4 (3.36)		22.6–36.1
LF (nu)		42.0 (2.80)		36.4–47.5		42.0 (2.80)		36.4–47.5		45.6 (2.83)		40.0–51.2		45.6 (2.83)		40.0–51.2
HF (nu)		50.1 (2.77)		44.6–55.6		54.2 (2.79)*		48.7–59.7		48.2 (2.82)		42.6–53.8		53.0 (2.82)*		47.4–58.6
LF/HF		1.32 (0.17)		0.96–1.67		1.14 (0.18)		0.77–1.49		1.47 (0.18)		1.11–1.83		1.07 (0.18)		0.71–1.43
RR		14.7 (0.66)		13.4–16.0		15.5 (0.65)*		14.2–16.8		15.0 (0.65)		13.7–16.3		16.7 (0.65)*		15.4–18.0
GSR		2.38 (0.69)		1.01–3.75		2.13 (0.71)		0.72–3.54		3.51 (0.69)		2.13–4.88		3.57 (0.69)		2.19–4.94

*P<0.05 - significant. Values are estimated marginal mean and SE with 95% CI. SFP: Spinal flexion-based postures, SEP: Spinal extension-based postures, average NN: Average time interval between normal-to-normal intervals, SDNN: Standard deviation of NN intervals, RMSSD: The root mean square of the mean of the sum of the squares of differences between adjacent NN intervals, pNN50: Percentage of the number of pairs of adjacent NN interval difference by >50 ms, HF (nu): High frequency normalized units, LF (nu): Low frequency normalized units, RR: Respiratory rate, GSR: Galvanic skin resistance, SE: Standard error, CI: Confidence interval

Regarding EGG parameters, the gastric motility, bradygastria power, normogastria power, and percentage of bradygastria decreased after both interventions. In contrast, tachygastria power, percentage of normogastria, and percentage of tachygastria increased following both interventions. Dominant frequency of bradygastria decreased after SFP and increased after SEP, while dominant frequency of tachygastria increased after SFP and decreased after SEP. However, these changes were also not statistically significant [Figure 3].

Figure 3.

Changes in electrogastrogram. SFP = Spinal flexion-based postures, SEP = Spinal extension-based postures

There was no significant effect of the sequence or time period in which interventions were administered suggesting that the order in which participants received the interventions did not substantially influence the outcome. The interaction between intervention and time point was not statistically significant indicating that there was no significant difference between the two interventions in terms of their impact on the primary outcomes [Table 3].

Table 3.

Effect of sequence, time point, and intervention interactions

Fixed effects parameter estimates
Names		Effect		Estimate		SE		95% CI				df		t		P
								Lower		Upper
Intercept		Intercept		0.0527		0.0152		0.0230		0.0824		152		3.477		<0.001
Intervention 1		SFP - SEP		0.0286		0.0303		−0.0308		0.0880		152		0.944		0.346
Sequence 1		2–1		0.0306		0.0303		−0.0288		0.0900		152		1.010		0.314
Time point 1		Pre–post		0.0314		0.0303		−0.0280		0.0908		152		1.035		0.302
Intervention 1 × sequence 1		SFP - SEP × 2–1		0.0607		0.0606		−0.0581		0.1796		152		1.002		0.318
Intervention 1 × time point 1		SFP - SEP × pre–post		0.0602		0.0606		−0.0586		0.1791		152		0.994		0.322
Sequence 1 × time point 1		2–1 × pre–post		0.0622		0.0606		−0.0566		0.1811		152		1.027		0.306
Intervention 1 × sequence 1 × time point 1		SFP - SEP × 2–1 × pre–post		0.1175		0.1212		−0.1201		0.3551		152		0.969		0.334

P<0.05 considered significant. SFP: Spinal flexion-based postures, SEP: Spinal extension-based postures, SE: Standard error, CI: Confidence interval, df: Degree of freedom

Discussion

The study aimed to evaluate the effects of two yoga-based interventions SFP and SEP on the ANS activation in moderately experienced yoga practitioners. The results show that the HF (nu) component of HRV had a significant main effect on the within-subjects factor “time point,” indicating a statistically significant increase in the HF after both the interventions. This shows that both SFP and SEP produced parasympathetic predominance immediately postintervention. Further, between-group comparison revealed no significant difference, indicating that both interventions produced similar effects. These findings are concurrent with previous studies that have used combination of spinal flexion and extension-based yoga postures and assessed cardiac autonomic modulation using HRV.[19,20] In the current study, both SFP and SEP interventions were performed with deep breathing which probably resulted in vagus nerve stimulation explaining the parasympathetic activation.[21]

Both SFP and SEP involve dynamic spinal movements, which activate proprioceptors in the muscles and joints, providing constant feedback to the CNS. This feedback likely contributes to enhanced body awareness, or interoception, which plays a crucial role in autonomic regulation.[22] As participants moved through these asanas, sensory signals from the body may have facilitated an improved understanding of internal states, leading to better autonomic balance. Moreover, spinal flexion and extension engage mechanoreceptors that are involved in the regulation of sympathetic and parasympathetic nervous systems, promoting a shift toward parasympathetic dominance during the postures.[23] These combined factors – proprioceptive feedback, interoception, spinal movements, and controlled breathing – likely worked together to induce parasympathetic activation and balance autonomic modulation following both interventions.

RR also showed a significant main effect on the within-subjects factor “time point,” indicating a statistically significant increase in the RR after both the interventions. Generally, yoga is considered a low-intensity exercise and studies have found decrease in RR postyoga practice.[24] However, the current study employed slightly more advanced postures like halasana and chakrasana requiring higher energy expenditure.[25] This could potentially explain the increase in RR due to effort of practice.

The electrodermal activity, measured using GSR, showed no significant changes in either of the two interventions. Previous studies have reported that yoga practice induces a relaxation response as indicated by significant drop in GSR, however most of them studied interventions based on yogic breathing, meditation, or relaxation.[26] The evidence for change in GSR purely due to yoga posture practice is inconclusive. Potential confounders, such as individual differences in stress response or measurement sensitivity, should be considered in future research. In addition, improvements in electrode placement and data acquisition methods might enhance the reliability of GSR measurements.

To the best of our knowledge, the current study is the first of its kind to explore the effects of yoga postures on gastric myoelectric activity. There was a nonsignificant decrease in overall gastric motility after both SFP and SEP interventions. This could be due to the activation of vagus nerve during the yoga intervention leading to reduced gastric myoelectric frequency via vagal efferents.[27] There was not much significant difference in the dominant power, dominant frequency and percentage distribution of bradygastria, normogastria, and tachygastria for either of the two interventions. The EGG recordings were limited to a brief 5-min duration, which may have been insufficient to detect significant changes. In addition, there was a delay of 1–2 min postintervention to place the electrodes and prepare the participant for recording. This delay could have resulted in the loss of critical data immediately following the intervention. Consequently, the full immediate postintervention effects might not have been captured. Future studies should use continuous EGG monitoring during and after interventions to capture the full range of effects.

The strengths of the current study include the utilization of multiple modalities to measure autonomic activity, specifically HRV, galvanic skin resistance (GSR), and electrogastrogram (EGG). Unlike most previous research, which has focused on either novice or highly experienced yoga practitioners, this study examines participants with moderate yoga experience, offering a more realistic representation of typical practice scenarios. Future research should aim for greater methodological rigor and incorporate more advanced and sensitive autonomic function measurement techniques to accurately assess immediate postintervention effects. In addition, investigating the long-term effects of flexion versus extension-based postures, as opposed to the single-session intervention employed in the current study, could provide more comprehensive insights.

Conclusion

This study explored the effects of spinal flexion and extension-based yoga postures on ANS activity in moderately experienced yoga practitioners using multiple modalities, including HRV, galvanic skin resistance (GSR), and electrogastrogram (EGG). Both interventions, spinal flexion-based postures (SFP) and spinal extension-based postures (SEP), significantly induced parasympathetic dominance in the ANS. The RR showed a significant increase postintervention, potentially due to the higher energy demands of advanced postures. GSR measurements revealed no significant changes, which aligns with previous findings that yoga’s relaxation effects are more pronounced with practices focusing on breathing and meditation rather than postures alone. Although the study did not find significant changes in gastric myoelectric activity, likely due to the short EGG recording duration and postintervention preparation time, it provided valuable insights into the vagal activation effects of yoga postures. These findings suggest that both flexion- and extension-based yoga postures, when performed with deep breathing, can effectively activate parasympathetic pathways, highlighting their potential use in stress management and autonomic modulation in clinical or therapeutic settings. Future research should explore long-term interventions and refine measurement methodologies to further elucidate the physiological mechanisms and broader applications of yoga practices.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.