# Abstract

 

## Background Chronic work-related stress is an independent risk factor for cardiometabolic diseases and associated mortality, particularly when compounded by a sedentary work environment. The purpose of this study was to determine if an office worksite-based *hatha* yoga program could improve physiological stress, evaluated *via* heart rate variability (HRV), and associated health-related outcomes in a cohort of office workers. 

## Methods Thirty-seven adults employed in university-based office positions were randomized upon the completion of baseline testing to an experimental or control group. The experimental group completed a 10-week yoga program prescribed three sessions per week during lunch hour (50 min per session). An experienced instructor led the sessions, which emphasized *asanas* (postures) and *vinyasa* (exercises). The primary outcome was the high frequency (HF) power component of HRV. Secondary outcomes included additional HRV parameters, musculoskeletal fitness (i.e. push-up, side-bridge, and sit & reach tests) and psychological indices (i.e. state and trait anxiety, quality of life and job satisfaction). 

## Results All measures of HRV failed to change in the experimental group versus the control group, except that the experimental group significantly increased LF:HF (p = 0.04) and reduced pNN50 (p = 0.04) versus control, contrary to our hypotheses. Flexibility, evaluated *via* sit & reach test increased in the experimental group versus the control group (p \< 0.001). No other adaptations were noted. *Post hoc* analysis comparing participants who completed ≥70% of yoga sessions (n = 11) to control (n = 19) yielded the same findings, except that the high adherers also reduced state anxiety (p = 0.02) and RMSSD (p = 0.05), and tended to improve the push-up test (p = 0.07) versus control. 

## Conclusions A 10-week *hatha* yoga intervention delivered at the office worksite during lunch hour did not improve HF power or other HRV parameters. However, improvements in flexibility, state anxiety and musculoskeletal fitness were noted with high adherence. Future investigations should incorporate strategies to promote adherence, involve more frequent and longer durations of yoga training, and enrol cohorts who suffer from higher levels of work-related stress. 

## Trial registration [ACTRN12611000536965](#) # Results 

## Flow of participants Forty-two individuals (n = 42) expressed an interest in the study, and were deemed eligible; five withdrew prior to baseline testing with reasons presented in Figure [1](#). Thirty-seven individuals provided written informed consent, completed baseline testing, and were randomized to the yoga (n = 18) or control group (n = 19). One participant in the yoga group withdrew in week 2 for personal reasons, while two in the control group failed to complete follow-up testing. Recruitment resulted in lower participant interest and enrolment than anticipated \[[22](#)\], and therefore our *a priori* calculation of statistical power was reduced from 80% to 63%. <figure> <p><img src="" /></p> <figcaption><strong>Flow of participants.</strong> * Baseline data carried forward for 1 yoga and 2 control participants lost to follow-up.</figcaption> </figure> 

## Baseline characteristics Participant characteristics are presented in Table [1](#). No statistically significant differences were observed between groups at baseline on the descriptive characteristics presented. However, due to potentially clinically important differences in BMI (p = 0.09), this variable was included as a covariate in all ANCOVA models. The cohort ranged in age from 21 to 58 years. BMI ranged from 18.3 to 39.2 kg/m^2^, and seven participants fulfilled the clinical criteria for obesity (i.e. BMI ≥30.0 kg/m^2^). Two participants were current smokers, while one had a history of tobacco use but did not currently smoke. Other than obesity, the most common chronic conditions were asthma (n = 4), hypercholesterolemia (n = 4) and hypertension (n = 5). None of the participants were presently engaged in regular yoga practice but nearly half had prior experience at a beginner level (17/37, 46%). The majority of participants were administrative staff, technical support staff, or post-graduate students. ::::table-wrap

::: caption
Baseline characteristics of the total cohort and groups
:::

**Characteristic** **Total cohort (n = 37)** **Yoga group (n = 18)** **Control group (n = 19)**

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Age (y) 38 ± 12 37 ± 12 39 ± 13
Women:Men 30:7 14:4 16:3
Body weight (kg) 68.6 ± 11.8 68.1 ± 10.7 69.1 ± 13.0
Height (cm) 165 ± 9 167 ± 9 163 ± 7
Body Mass Index (kg/m^2^) 25.3 ± 4.8 24.4 ± 4.0 26.1 ± 5.6
Systolic blood pressure (mmHg) 121 ± 12 122 ± 14 121 ± 9
Diastolic blood pressure (mmHg) 79 ± 10 79 ± 11 80 ± 8
Occupation (n):
• Administrative staff 13 7 6
• Technical support 10 4 6
• Post-graduate student 8 3 5
• Academic staff 5 3 2
• Research staff 1 1 0

Data presented as mean ± standard deviation.:::: 

## Correlations between measures of HRV at baseline Correlation coefficients relating to measures of HRV in the total cohort at baseline, after normalization of data, are presented in Table [2](#). Log SDNN, log RMSSD, pNN50, log LF power, log HF power and log total power were positively, significantly and highly correlated (all p \< 0.001; all *r* ≥0.69). Log LF:HF was negatively, significantly and moderately correlated with pNN50 (p = 0.02), log RMSSD (p = 0.01) and log HF power (p \< 0.001). Resting heart rate was significantly, negatively and moderately correlated with log SDNN (p = 0.004), log RMSSD (p = 0.001), pNN50 (p = 0.003), log LF power (p = 0.02), log HF power (p = 0.003) and log total power (p = 0.01). ::::table-wrap
::: caption
Correlations among measures of heart rate variability and heart rate
:::

**Log SDNN** **Log RMSSD** **pNN50** **Log LF power** **Log HF power** **Log total power** **Log LF:HF** **Resting HR**

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Log SDNN   0.91^*^ 0.76^*^ 0.75^*^ 0.76^*^ 0.83^*^ −0.23 −0.48^*^
Log RMSSD     0.81^*^ 0.69^*^ 0.84^*^ 0.83^*^ −0.44^*^ −0.57^*^
pNN50       0.73^*^ 0.85^*^ 0.82^*^ −0.41^*^ −0.48^*^
Log LF Power         0.80^*^ 0.92^*^ 0.06 −0.39^*^
Log HF Power           0.94^*^ −0.56^*^ −0.49^*^
Log Total Power             −0.28 −0.44^*^
Log LF:HF               0.27

\*p \< 0.05; *SDNN*, standard deviation of the normal-normal interval;
*RMSSD*, root-mean-square of the successive normal sinus RR interval
difference; *pNN50*, percentage of absolute differences between
successive normal RR intervals that exceed 50 ms; *HF*, high frequency
power; *LF*, low frequency power; *LF:HF*, ratio of low frequency to
high frequency power; *HR*, heart rate.:::: 

## Correlations between state anxiety and HRV measures Higher levels of state anxiety were associated with higher resting heart rate (r = 0.51, p = 0.002), lower pNN50 (r = -0.36, p = 0.03), lower log RMSSD (r = -0.39, p = 0.02), lower log LF power (r = -0.344, p = 0.05), lower log HF power (r = -0.47, p = 0.01), and lower log total power (r = -0.40, p = 0.02). 

## Attendance and adverse events Attendance in the yoga group ranged from 33% to 97% and averaged 73 ± 19%. Eleven participants (11/17, 65%) attended ≥70% of the sessions. No adverse events were documented in either the experimental or control group during the study. 

## Outcome measures All outcome measures are presented in Table [3](#). ::::table-wrap
::: caption
Summary of primary and secondary outcome measures
:::

**Yoga group** **Control group** **Effect size** **p**^\*\*\*\*\*^

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**Outcome measure** **Week 0** **Week 11** **Week 0** **Week 11**\
***HRV and Heart Rate***\
Log HF Power 2.75 ± 0.63 2.51 ± 0.83 2.57 ± 0.58 2.53 ± 0.55 0.02 0.48
Log SDNN 1.81 ± 0.21 1.76 ± 0.28 1.69 ± 0.19 1.68 ± 0.19 0.01 0.70
Log RMSSD 1.73 ± 0.32 1.59 ± 0.42 1.58 ± 0.29 1.62 ± 0.27 0.05 0.22
pNN50 27.7 ± 27.5 20.7 ± 25.3 16.0 ± 16.6 19.4 ± 18.4 0.12 0.04
Log LF Power 2.89 ± 0.57 2.86 ± 0.73 2.61 ± 0.45 2.55 ± 0.49 0.01 0.53
Log Total Power 3.34 ± 0.50 3.26 ± 0.64 3.18 ± 0.42 3.09 ± 0.42 0.01 0.66
Log LF:HF 0.13 ± 0.33 0.35 ± 0.43 0.04 ± 0.40 0.04 ± 0.38 0.12 0.04
Heart Rate (beats/min) 62 ± 6 65 ± 9 68 ± 10 67 ± 9 0.07 0.13
***Musculoskeletal Fitness***\
Sit and reach (cm) 27.8 ± 10.0 31.0 ± 8.7 27.3 ± 11.0 26.4 ± 10.4 0.35 \<0.001
Push-up (reps) 17 ± 10 21 ± 11 17 ± 13 20 ± 13 0.04 0.27
Side bridge (s) 60.1 ± 35.3 60.8 ± 38.7 47.0 ± 27.2 42.9 ± 24.7 0.01 0.59
***Psychological Measures***\
Trait Anxiety (STAI) 36.1 ± 10.4 33.1 ± 9.7 38.6 ± 7.8 35.3 ± 7.2 0 0.96
State Anxiety (STAI) 32.7 ± 6.2 27.9 ± 7.6 36.1 ± 9.7 32.1 ± 7.8 0.04 0.25
General Job Satisfaction (JIG) 46.9 ± 7.6 47.1 ± 7.7 46.3 ± 6.0 46.7 ± 6.2 0.01 0.52
PCS (SF36) 49.4 ± 2.9 47.5 ± 2.7 47.4 ± 5.1 46.9 ± 4.8 0.04 0.27
MCS (SF36) 45.3 ± 8.9 47.5 ± 10.6 45.2 ± 923 48.5 ± 7.7 0.01 0.66

Data presented as mean + standard deviation.

^\*^Estimates based upon the final model including the baseline
assessment value, age and body mass index as covariates.

*SDNN*, standard deviation of the normal-normal interval; *RMSSD*,
root-mean-square of the successive normal sinus RR interval difference;
*pNN50*, percentage of absolute differences between successive normal RR
intervals that exceed 50 ms; *HF*, high frequency power; *LF*, low
frequency power; *LF:HF*, ratio of low frequency to high frequency
power; *STAI*, State-trait anxiety inventory; *JIG*, Job in general
scale; *SF36*, medical outcomes trust short-form 36 health status
questionnaire; *PCS*, physical component scale; *MCS*, mental component
scale.:::: 

### HRV and heart rate Log HF, the primary outcome, did not significantly improve in the yoga group versus the control group over time (p = 0.48). Contrary to our hypotheses, the yoga group significantly reduced pNN50 (p = 0.04) and increased log LF:HF (p = 0.04) versus the control group. No group × time interaction effects were noted for log SDNN, log RMSSD, log LF power, log total power or resting heart rate (Table [3](#)). 

### Musculoskeletal fitness Low back and hip flexibility, evaluated *via* sit and reach test, significantly increased in the yoga group versus the control group following the intervention period (p \< 0.001). No group × time interaction effect was noted for the push-up test or the side-bridge test (Table [3](#)). 

### Psychological health status None of the QoL domain scores changed significantly in the yoga group versus the control group following the intervention period (data not shown, all p > 0.05), nor were group × time effects noted for the QoL summary scales (i.e. Physical Component Scale and Mental Component Scale; Table [3](#)). Both groups reduced state and trait anxiety measures from pre to post intervention; however, no significant group × time interaction effects were noted. None of the five domains of job satisfaction measured *via JDI* changed significantly between groups over time (data not shown, p > 0.05), nor did general job satisfaction measured *via JIG* (Table [3](#)). 

## Post hoc analyses *Post-hoc* analyses were conducted to evaluate the effect of adherence on adaptation. ANCOVA of the post-treatment score controlling for the baseline score, age and BMI were computed for all outcome measures between participants who attended ≥70% of the yoga sessions (n = 11) versus the control group (n = 17). The findings remained unchanged from the primary analysis, except that the high adherers to yoga significantly reduced state anxiety (p = 0.02) and RMSSD (p = 0.05), and tended to improve the push-up test (p = 0.07) versus the control group.


Extracted trial result:
Outcome: pNN50 (continuous)
Intervention: 10-week yoga program
Comparator: Control
Intervention group size: 18
Intervention mean: 20.7
Intervention standard deviation: 25.3
Comparator group size: 19
Comparator mean: 19.4
Comparator standard deviation: 18.4
Notes: Numerical values are from Week 11.