Effects of Surya Namaskar yoga on perceived stress, anthropometric parameters, and physical fitness in overweight and obese female university students: A randomized controlled trial

Abstract

Background:

Stress and sedentary lifestyles negatively impact the physical fitness of overweight and obese female university students. Physical activity has been shown to promote psychological as well as physical wellness. However, the effects of Surya Namaskar (SN) yoga on stress and physical fitness remain unclear.

Objective:

This study aimed to compare the physical fitness, anthropometric measures, and perceived stress between the SN yoga training program group and the control group.

Methods:

In a randomized controlled study, 44 overweight and obese female university students participated. For 8 weeks, the exercise group received training in SN yoga, whereas the control group was not permitted to participate in any form of exercise. At baseline and after 8 weeks of training, all participants completed the Thai Perceived Stress Scale-10 (T-PSS-10), and assessed the body mass index (BMI), waist–hip ratio, body fat percentage, maximum oxygen consumption (VO₂max), and muscle strength and flexibility. We used the dependent t-test or Wilcoxon sign rank test to examine the differences between the T-PSS-10 and physical fitness within each group. The statistical differences of all parameters between the two groups were compared using an independent t-test or a Mann–Whitney U test. A p-$\mathrm{\text{value}}<0.05$ was considered statistically significant.

Results:

Compared to the baseline, the SN yoga group’s post-training period had a significant increase ($p<0.05$) in forward back flexibility, hand grip strength, leg strength, and VO₂max, while a significant decrease ($p<0.05$) in T-PSS-10 scores and BMI. In addition, we found a significant difference between the both groups in forward back flexibility and T-PSS-10 scores in the post-training period ($p=0.015$ and $p=0.009$, respectively).

Conclusion:

This study’s findings demonstrated that SN yoga is a useful exercise for enhancing overweight and obese female university students’ perceived stress scales and physical fitness.

Introduction

The modern lifestyle is leading to a drop-in physical activity (PA) and exercise as well as a substantial change in human nutrition, including an energy-rich diet and fast food. Non-communicable diseases include obesity, diabetes mellitus, hypertension, and cardiovascular disease are mostly caused by a poor diet and insufficient PA.¹ Overweight and obesity are becoming more prevalent worldwide. In 2013, the estimated prevalence of adults with a body mass index (BMI) $\ge 25$ kg/m² was 36.9% in males and 38.0% in female. Overweight and obesity are more common in children and adolescents in developed countries, with 23.8% of boys and 22.6% of girls diagnosed.² Excess energy uptake causes adipocyte hypertrophy, hyperplasia, and the production of visceral fat in non-adipose tissues, which can lead to cardiovascular illness and liver disease. Adipose tissue can also secrete adipokines and inflammatory cytokines, which can alter the local microenvironment, induce insulin resistance, hyperglycemia, and activate inflammatory signalling pathways. This aggravates the onset and progression of obesity-related illnesses.³ According to previous studies, many university students studying healthcare sciences have improper behaviours regarding PA and a nutritious diet.^4,5 Additionally, a high prevalence of obesity and overweight was observed among college students studying health sciences.^6,7,8 Obesity negatively impacts the individual’s physical and mental well-being. Regarding the impact on physical health, co-morbidities related to being overweight or obese include respiratory disorders, sleep apnea, osteoarthritis, dyslipidemia, type 2 diabetes, hypertension, coronary heart disease, stroke, gallbladder disease, and some malignancies.⁹ Obesity is strongly linked to anxiety and depression in terms of its effects on mental health.¹⁰ An imbalance between a person’s expectations and their capacity for coping is termed as stress.¹¹ Obesity and stress are also strongly associated.¹² Weight stigma is highly prevalent, which makes being obese a stressful situation.¹³ On the other hand, stress can promote excessive consumption of high-calorie foods and beverages, reduce PA, and shorten sleep, all of which can contribute to behaviour-induced obesity.¹² University students studying healthcare sciences have shown evidence of negative relationships between stress and anthropometric parameters [waist–hip ratio (WHR), body fat percentage, and BMI] as well as physical fitness parameters (cardiorespiratory fitness, muscular strength, and flexibility).^14,15,16,17

PA is any activity, such as exercise or housework, which triggers the body to contract various skeletal muscles and requires a greater amount of energy.¹ Numerous research works have shown that PA promotes positive effects on both mental and physical health.^18,19,20,21 Yoga is a simple PA that has been gaining popularity as a holistic physical–spiritual therapy. Sun salutation yoga, also known as Surya Namaskar (SN), is a sequence of 12 dynamic steps that combines asana (posture), pranayama (yogic breathing), and dharana (deep concentration).²² SN yoga incorporates focused breathing exercises and meditation. It is a body–mind practice that assists in minimizing stress and anxiety while promoting mental calmness.²³ Slow breathing exercises could lower the sympathetic nervous system, heart rate, blood pressure at both systolic and diastolic levels, cortisol, or stress hormone, and the perception of stress.²⁴ Previous research indicated that SN yoga improved physical relaxation and mental calm, as well as stress dispositions such as somatic stress concern and negative emotions in students and university students.^25,26,27 In addition, SN yoga could contribute to decreasing body fat percentage in overweight and obese people as well as the waist–hip circumference, BMI, and waist circumference.^28,29 It was previously revealed that practicing this yoga could enhance muscular strength, flexibility, and cardiorespiratory fitness.^30,31,32 Furthermore, previous studies found that yoga improves stress in the obese population.^33,34,35

Students studying healthcare sciences at universities were the study’s special target group because they will eventually work in the medical field and will be directly in charge of health promotion. They will give the wrong impression to the public if they are obese. Furthermore, because they were health science students, they were particularly susceptible to stress from several factors such as difficult academic assignments, demanding responsibilities, and a competitive academic environment.^36,37,38 Additionally, female university students reported greater stress-related issues, such as low self-esteem, academic stress, and social relationship, than males.^39,40 These factors could have a negative impact on both mental and physical health. SN yoga is a holistic physical–spiritual therapy which could improve stress and physical fitness. In addition, SN yoga was found to be statistically more significant in reducing stress levels than aerobic exercise.⁴¹ However, it appears to provide limited and insufficiently understood effects on stress levels and physical fitness in overweight and obese university students. Accordingly, the purpose of this study was to compare the physical fitness, anthropometric parameters, and stress levels of obese and overweight female physical therapy students who participated in the SN yoga training program with a control group.

Materials and Methods

Study design

This single-blinded, randomized controlled trial was performed to compare the effects of SN yoga on perceived stress, anthropometric parameters, and physical fitness in overweight and obese female physical therapy students. The outcome evaluations were carried out both before and after the 8-week exercise program. The outcome assessor was blinded by the allocation of participants to the experimental and control groups. The trial was registered through the Thai clinical trials registry with the following registration number: TCTR20230907005.

Participants

Forty-four participants were purposive sampling in this study. They were recruited via poster and personal contact. The following criteria were required for inclusion: (1) female university students in the School of Allied Health Sciences, Department of Physical Therapy, University of Phayao; (2) age range of 19 to 22 years; (3) BMI $\ge 23$ kg/m² was considered overweight or BMI $\ge 25$ kg/m² were classified as obese⁴²; and (4) no major adverse health conditions, such as hypothyroidism, heart disease, asthma, hypertension, myopathy, or serious mental health diagnoses. Participants who engaged in another exercise during participating in this study were excluded. Randomization of participants to the exercise group or sedentary lifestyle (control) group was performed by blocked randomization using a computer-generated randomization list that assigned 22 participants to each group.⁴³ All the participants provided written informed consent to participate, and the study was approved by the Human Ethical Committee at the University of Phayao (protocol code UP-HEC 1.2/071/66 and date of approval, 2 May 2023).

Sample size calculation

The sample size of each group was calculated using n4Studies.^44,45 We used the two independent means based on our pilot study with the minimal detectable difference of the mean of two groups was 4.28 scores of the Thai version of the Perceived Stress Scale-10 (T-PSS-10), with a standard deviation of 5.32 and 4.13 scores of two groups. An alpha level of 0.05 and a power factor of 80% were considered in the determination. Therefore, the minimum sample size for each group was 20. Considering the 10% drop-out, 22 persons/groups were required for the study.

Outcome measurements

Demographic information was collected at baseline. The participants completed the TPSS-10 questionnaire at baseline and after 8 weeks of the exercise program. All outcomes were assessed by the assessors blinded to the randomization before and after exercise program. The assessors were two physical therapy students who had received administration training from an experienced physical therapist. The first assessor evaluated BMI, WHR, body fat percentage, and forward trunk flexibility. The second assessor evaluated grip and leg muscle strength and VO₂max.

Perceived stress

The Perceived Stress Scale (PSS) is a well-known self-assessment instrument that measures as stressful life events are perceived that have occurred over the previous month. There are 10 items on this five-point Likert scale, which goes from 0 (never) to 4 (very often). Higher composite scores correspond to higher levels of perceived stress along a scale of 0 to 40. With a Cronbach’s alpha of 0.84 and an interclass correlation value of 0.83 (95% confidence range, 0.722–0.881), the T-PSS-10 has shown strong validity and reliability for evaluating the level of stress perception in a Thai population.⁴⁶

BMI, WHR, and body fat percentage

Each participant was measured in weight and height to calculate their BMI. WHR was calculated by dividing waist circumference by hip circumference (in centimetres).⁴⁷ The optimal points to measure for waist and hip circumferences were midway between the costal margin and the iliac crest and at the largest part above the buttocks, respectively. Body fat percentage was measured at four sites, including the triceps, biceps, subscapular, and suprailiac crest, via the skinfold thickness technique (Lange skinfold caliper, Beta Technology, Santa Cruz, CA, USA).⁴⁸

Grip and leg strength

To evaluate grip strength, each participant performed the hand grip dynamometer (T.K.K 5001 Grip-A, Takei Scientific Instruments, Niigata, Japan) three times with a 1-min rest interval in between. The best grip strength (in kilograms) was divided by the participant’s body weight (kilograms) for relative grip strength.⁴⁹ Participant’s leg strength was determined via a back and leg dynamometer (T.K.K 5402 Back-D, Takei Scientific Instruments, Niigata, Japan) for two trials with a 1-min rest interval. Similarly, the relative leg strength was calculated from the best score of the leg muscle strength test (in kilograms) divided by the participant’s body weight (kilograms).

Forward trunk flexibility

A modified sit-and-reach with a standing trunk flexion meter (T.K.K. 5403 Flexion-D, Takei Scientific Instruments, Niigata, Japan) was used to evaluate forward trunk flexibility. The participants tried to push a yard stick placed on top of a 12-inch sit-and-reach box as far as possible. The most distant point of the fingertips on the yardstick was recorded in inches.⁵⁰

VO₂max

The participants applied for the Queens College step test at a rate of 22 steps per minute, for 3 min. After the test, heart rates (beats per minute; bpm) were recorded. Then, the predicted VO₂max (millilitres/kilogram/minute; ml/kg/min) can be calculated.⁵¹

Exercise program

A physical therapist gave all the participants in both groups an hour-long session about the advantages of PA and appropriate diets. SN yoga was provided as an exercise program for the experimental group’s participants. After three sessions a week for 8 weeks, the program was finished. A skilled yoga instructor trained each participant and gave them three sessions of practice correction during the first week. After that, participants were instructed to complete these activities as part of a 7-week home program using a video recording as the teaching media. The 10-min warm-up begins the 50-min SN yoga training program. Then, the participants did 12 SN yoga positions for 30 min. There will be a 10-min cool-down period after this. The sequences of 12 poses of the SN yoga cycle are as follows: the prayer pose, raised arm pose, arm to leg posture, equestrian pose, stick pose, eight-limbed pose, cobra style, face down dog, high lunge, standing forward bend, raised arm pose, and the prayer pose.⁵² The participants in the experimental group were required to begin and continue practicing following video recording of SN yoga practice until it ended. They had to give the researchers access to the checklist of SN yoga practice completed for each session of the 7-week home program. Throughout the 8 weeks, participants in the control group did not engage in any exercise.

Statistical analysis

Descriptive statistics were used to explain demographic data and the findings of the study. All data were tested for normally distributed patterns by the Kolmogorov–Smirnov test. The chi-square test was used to examine the differences between categorical variables between the two groups. The independent t-test for parametric data or Mann–Whitney U test for non-parametric data was used to compare the differences in the age, weight, height, BMI, T-PSS-10 scores, anthropometric parameters, and physical fitness between both groups. To analyse the differences in the parameters within each group, the dependent t-test for parametric data, or Wilcoxon sign rank test for non-parametric data was used. A p-$\mathrm{\text{value}}<0.05$ was considered statistically significant.

Results

Figure 1 shows the study’s participant flow diagram in accordance with the Consolidated Standards of Report Trials (CONSORT) declaration. Out of 180 female university students screened for eligibility, 44 persons were included. One participant from the SN yoga group was excluded due to a loss in follow-up. The study was completed by 43 participants, whose mean age was $20.18\pm 1.17$ years. Table 1 presents the participants’ demographic characteristics. Between the SN yoga group and the control group, there was a non-statistically significant difference at baseline.

Fig. 1.

Flow diagram for recruitment of participants.

Table 1.

Demographic characteristics of participants in the SN yoga group and a control group.

Parameters	Control ($n=22$)	SN yoga ($n=21$)	p-Value
Agea (years), $\mathrm{\text{mean}}\pm \mathrm{\text{SD}}$	$20.36\pm 1.05$	$20.29\pm 0.96$	0.801
Weightb (kilograms), $\mathrm{\text{mean}}\pm \mathrm{\text{SD}}$	$78.98\pm 10.10$	$80.08\pm 15.53$	0.784
Highb (centimetres), $\mathrm{\text{mean}}\pm \mathrm{\text{SD}}$	$159.64\pm 7.40$	$161.14\pm 6.24$	0.472
BMIb (kg/m2), $\mathrm{\text{mean}}\pm \mathrm{\text{SD}}$	$31.05\pm 3.93$	$30.71\pm 4.82$	0.798
Overweightc (23–24.49 kg/m2)	10 (45.5)	10 (47.6)	0.887
Obesec ($\ge 25$ kg/m2)	12 (54.5)	11 (52.4)	0.887
Underlying disease,cn (%)	0 (0)	0 (0)	—
Regular exercise,cn (%)	6 (27.3)	8 (38.1)	0.449
Cigarette smoking,cn (%)	0 (0)	1 (4.8)	0.300
Alcohol use,cn (%)	4 (18.2)	5 (23.8)	0.650
Insufficient family income,cn (%)	5 (22.7)	5 (23.8)	0.650
Skipping breakfast,cn (%)	6 (29.1)	10 (47.6)	0.092
Skipping meals,cn (%)	14 (63.6)	9 (42.9)	0.172
Snack between meals,cn (%)	18 (81.8)	14 (66.7)	0.225
Sleep $<6$ h/day,cn (%)	6 (27.3)	8 (38.1)	0.449

Notes: BMI, body mass index; kg/m², kilograms per square meter; n, number; kg/m², kilograms per square meter; SD, standard deviation. ^aAnalysed via the Mann–Whitney U test, ^banalysed via the independent samples ttest, ^canalysed via the chi-square test.

Tables 2 and 3 present the comparisons between the anthropometric parameters, physical fitness, and T-PSS-10 scores within the SN yoga group and the control group at baseline and after 8 weeks of the trial period. The findings demonstrated that the T-PSS-10 scores and BMI were significantly decreased while forward back flexibility, hand grip strength, leg strength, and VO₂max were significantly increased at the post-training compared to the baseline in the SN yoga group. For the control group, however, there was no statistically significant difference in any of the parameters. Furthermore, after training, the independent sample t-test revealed a significant difference in the T-PSS-10 scores and forward back flexibility between the two groups ($p=0.015$ and $p=0.009$, respectively) (Fig. 2).

Table 2.

Comparisons of the T-PSS-10 scores, anthropometric parameters, and physical fitness within the SN yoga group (n = 21) at the baseline and after 8 weeks of experimental period.

Parameters	Baseline ($\mathrm{\text{Mean}}\pm \mathrm{\text{SD}}$)	Week 8 ($\mathrm{\text{Mean}}\pm \mathrm{\text{SD}}$)	p-Value
T-PSS-10 scoresa	$18.86\pm 6.73$	$14.38\pm 5.59$	0.009*
BMIa (kg/m2)	$30.71\pm 4.82$	$30.41\pm 4.54$	0.021*
WHRb	$0.85\pm 0.06$	$0.83\pm 0.05$	0.215
Body fatb (%)	$44.27\pm 1.20$	$44.41\pm 0.64$	0.601
Forward back flexibilityb (inch)	$4.62\pm 3.47$	$10.35\pm 6.40$	$<0.001$*
Relative hand grip strengthb	$0.31\pm 0.07$	$0.33\pm 0.06$	0.014*
Relative leg strengthb	$0.74\pm 0.25$	$0.95\pm 0.23$	$<0.001$*
VO2maxb (ml/kg/min)	$38.61\pm 2.86$	$40.72\pm 2.99$	$<0.001$*

Notes: BMI, body mass index; kg/m², kilograms per square meter; ml/kg/min, millilitres per kilogram per minute; SD, standard deviation; T-PSS-10, the Thai version of the Perceived Stress Scale-10; VO₂max, maximum oxygen consumption; WHR, waist–hip ratio. ^aAnalysed via the Wilcoxon signed rank test, ^banalysed via the paired samples t test, *p-$\mathrm{\text{value}}<0.05$.

Table 3.

Comparisons of the T-PSS-10 scores, anthropometric parameters, and physical fitness within a control group ($n=22$) at the baseline and after 8 weeks of experimental period.

Parameters	Baseline ($\mathrm{\text{Mean}}\pm \mathrm{\text{SD}}$)	Week 8 ($\mathrm{\text{Mean}}\pm \mathrm{\text{SD}}$)	p-Value
T-PSS-10 scoresa	$16.95\pm 5.77$	$18.45\pm 4.88$	0.130
BMIb (kg/m2)	$31.10\pm 3.85$	$31.02\pm 3.93$	0.424
WHRb	$0.85\pm 0.09$	$0.84\pm 0.08$	0.269
Body fatb (%)	$43.60\pm 1.97$	$44.02\pm 0.99$	0.257
Forward back flexibilityb (inch)	$5.74\pm 5.36$	$6.29\pm 6.09$	0.105
Relative hand grip strengthb	$0.32\pm 0.19$	$0.33\pm 0.23$	0.602
Relative leg strengthb	$0.72\pm 0.27$	$0.80\pm 0.24$	0.527
VO2maxa (ml/kg/min)	$39.63\pm 2.47$	$40.08\pm 2.07$	0.331

Notes: BMI, body mass index; kg/m², kilograms per square meter; ml/kg/min, millilitres per kilogram per minute; SD, standard deviation; T-PSS-10, the Thai version of the Perceived Stress Scale-10; VO₂max, maximum oxygen consumption; WHR, waist–hip ratio. ^aAnalysed via the paired samples t test, ^banalysed via the Wilcoxon signed rank test, *p-$\mathrm{\text{value}}<0.05$.

Fig. 2.

Comparisons of the T-PSS-10 scores, anthropometric parameters, and physical fitness between the SN yoga group ($n=21$) and a control group ($n=22$) at baseline and after 8 weeks of experimental period. Notes: BMI, body mass index; kg/m², kilograms per square meter; ml/kg/min, millilitres per kilogram per minute; T-PSS-10, the Thai version of the Perceived Stress Scale-10; VO₂max, maximum oxygen consumption. *Significant difference between groups, p-$\mathrm{\text{value}}<0.05$.

Discussion

This study assessed the perceived stress, physical fitness, and anthropometric parameters among female university students who were classified as overweight or obese and participated in the SN yoga training program, in comparison to a control group. Following an 8-week experiment period, the SN yoga group shown a significant increase in VO₂max, grip and leg strength, trunk flexibility, and a significant decrease in perceived stress and BMI as compared to baseline ($p<0.05$). We found that the control group had not significantly improved. Additionally, after 8 weeks of the study, there were significant differences between the SN yoga group and a control group in terms of perceived stress and trunk flexibility.

The results of this study showed that after completing the training program, the SN yoga group had a significantly lower perceived stress than a control group. Our findings were consistent with a study by Stec et al.²⁵ who found a significant decrease in stress levels among the students trained in dynamic SN yoga for 12 weeks. A previous study also found a significant reduction in PSSs in medical professionals who performed the SN yoga for 4 weeks.⁴¹ In addition, a study by Godse et al.²⁷ found that the college students who received SN yoga program had lower stress dispositions–somatic stress, worry, and negative emotions compared with the control group.²⁷ SN yoga consists of 12 body postures, focused breathing techniques and meditation. It is a body–mind technique that helps to reduce stress and anxiety while also increasing mental calmness. The purposeful guidance of breath promotes physical purification, immunity enhancement, and greater energy. It also helps improve mental clarity, inner serenity, and relaxation.²³ Slow breathing exercises may reduce the sympathetic nervous system, heart rate, blood pressure at both systolic and diastolic levels, cortisol, or stress hormone, and the perception of stress.²⁴

Our findings showed that following the training program, the SN yoga group’s flexibility, measured using a modified sit-and-reach test, was significantly higher than that of the control group. Our findings agreed with previous studies that showed the beneficial impacts of SN yoga on flexibility.^{52,53,54,55,56} According to Yuvaraja et al.,⁵⁵ 40 obese girls in the 15–17 age range performed better when they had SN yoga instruction 5 days a week for 12 weeks. This improved performance included increases in flexibility, cardio-respiratory endurance, and body weight decrease.⁵⁵ According to the other study, 25 obese college men’s flexibility and BMI might be improved by SN yoga combined with pranayama or meditation practice.⁵⁶ The SN yoga consists of 12 poses that combine stretching, holding, and relaxation. The sequence of motions permits the body to flex and extend the spine column and the upper and lower limbs through their complete range of motion. Extended stretches in many parts of the body are required for the SN yoga practice, which causes muscle and connective tissue to extend through elastic elongation, improving flexibility.⁵⁷

In this study, the SN yoga group showed significant improvements in VO₂max, grip and leg strength, and BMI after 8 weeks of the exercise program ($p<0.05$). Nonetheless, there were no significant differences in these parameters between the control group and the SN yoga group. Our findings contradicted those of other research, which found significant effects of SN yoga on anthropometric measurements, muscle strength, and cardiorespiratory fitness in overweight and obese individuals.^{55,56,57,58,59} The primary causes of these inconsistent effects may be the frequency and length of the SN yoga classes. Over 8 weeks, the SN yoga group performed three times a week of yoga as part of our study. In our study, the training program was conducted less often and for a shorter period than in the previous study, which continued for 12 weeks on 5 days a week.^55,58,59 We did not regulate either the group’s nutritional intake or their daily life, even though we informed them about recommendations for healthy eating and the advantages of exercise. These could have an impact on the efficacy of the training performed. To develop an effective yoga training program that improves anthropometric parameters and physical fitness in overweight and obese individuals, further studies on these issues should be conducted.

Clinical implication

Regarding the beneficial effects of SN yoga on forward trunk flexibility and perceived stress, health promoters might choose to consider this PA for improving physical fitness as well as coping with stress among obese female university students.

Limitations

Our study has some limitations. First, only overweight and obese female university students between the ages of 19 and 22 were included in this study. In the other age groups, such as children and elderly populations, further studies on both genders should be conducted. Second, with the small sample size, the study was underpowered to detect differences in some main outcomes between groups. Larger sample sizes along with further research are required. Finally, a self-report that may differ based on personal experience was applied to assess each person’s stress levels. To assess subjective stress levels, such as cortisol levels, further research should be considered.

Conclusion

The results of this study confirmed that SN yoga is an effective PA in improving perceived stress and trunk flexibility among overweight and obese female university students.

Conflict of Interest

The authors have no conflicts of interest relevant to this paper.

Funding/Support

There was no specific grant for this research from public, private, or non-profit funding organizations.

Author Contributions

Conceptualization and methodology, B.S., N.S., A.T., and W.T.; formal analysis and investigation, B.S.; writing — original draft preparation, B.S.; writing — review and editing, B.S., N.S., A.T., and W.T.; supervision, W.T. All authors have read and agreed to the published version of this paper.

ORCID

Boonsita Suwannakul   https://orcid.org/0000-0003-4716-657X

Noppharath Sangkarit   https://orcid.org/0000-0003-4622-5638

Ajchamon Thammachai   https://orcid.org/0000-0001-8800-5495

Weerasak Tapanya   https://orcid.org/0000-0002-7080-5213