Effect of an office worksite-based yoga program on heart rate variability: outcomes of a randomized controlled trial

This study investigated whether a 10-week hatha yoga program, delivered at an office worksite during lunch breaks, could improve physiological stress markers and other health-related outcomes in office workers.

The intervention was a 10-week hatha yoga program, consisting of three 50-minute sessions per week, led by an experienced instructor. The sessions emphasized asanas (postures) and vinyasa (exercises), starting with warm-ups, progressing through standing and floor poses, and concluding with breathing exercises (pranayama) and relaxation (savasana). Participants were encouraged to choose difficulty levels appropriate for them.

The comparator was a no-treatment control group, who were advised to maintain their current lifestyle practices and received no specific information or instructions about yoga.

The outcome measures included:

• Primary Outcome:
  • Heart Rate Variability (HRV): Specifically, the high frequency (HF) power component of HRV, measured in absolute units (ms²), which is considered a major indicator of parasympathetic nervous system (vagal) activity.
• Secondary Outcomes:
  • Additional HRV Parameters:
    • Standard deviation of the NN intervals (SDNN)
    • Root-mean-square of the successive normal sinus RR interval difference (RMSSD)
    • Percentage of absolute differences between successive normal RR intervals that exceed 50 ms (pNN50)
    • Low frequency (LF) power (ms²)
    • LF:HF ratio
    • Average heart rate (beats per minute)
  • Musculoskeletal Fitness:
    • Upper-body muscular endurance (via a standardized push-up test)
    • Low-back and abdominal endurance (via an isometric side-bridge test, averaging scores for left and right sides)
    • Low-back and hip flexibility (via a standardized sit-and-reach test)
  • Psychological Indices:
    • State anxiety and trait anxiety (using the State-Trait Anxiety Inventory - STAI)
    • Health-related quality of life (QoL) across eight domains and two summary scores (using the Medical Outcomes Trust Short-form 36 Health Status Questionnaire - SF36)
    • Job satisfaction (using the Job Descriptive Index - JDI, assessing supervision, co-workers, work, pay, and promotion; and the Job in General - JIG scale for overall satisfaction)

The study included 37 adults (specific gender breakdown not provided in the abstract, but randomization was stratified by gender) employed in university-based office positions at the University of Western Sydney.

Participants met the following eligibility criteria:

• Adults aged over 18 years.
• Employed full-time as academic staff, general staff, or post-graduate students at the University of Western Sydney.
• Not currently engaged in regular yoga practice.
• Available to attend three yoga sessions per week during their lunch break.
• Able to communicate in English.
• No acute or chronic medical conditions that would contraindicate hatha yoga practice.

The study population consisted of office workers, a group often characterized by sedentary work environments and potential chronic work-related stress.

• Heart Rate Variability (HRV) and Heart Rate:
  • Measured in a quiet, temperature-controlled room following established procedures from the Task Force for Pacing and Electrophysiology.
  • Participants abstained from caffeinated foods/beverages on the assessment day and avoided exercise for at least 24 hours prior.
  • Assessments were repeated at the same time of day and using the same procedures at baseline (week 0) and after the intervention (week 11), with experimental group participants tested at least 48 hours after their final yoga session.
  • After 15 minutes of supine rest with a regular, calm breathing pattern, a continuous 10-minute ECG recording was collected using the Sphygmocor system and HRV software (Sphygmocor, AtCor Medical Pty, Sydney, Australia).
  • Participants were instructed not to speak and to maintain a regular, calm breathing pattern during the entire assessment.
  • Time domain parameters (SDNN, RMSSD, pNN50) and frequency domain variables (total power, HF, LF, LF:HF ratio) were calculated from RR intervals. Heart rate was the average beats per minute during the 10-minute recording.
• Musculoskeletal Fitness:
  • Upper-body muscular endurance: Evaluated using a standardized push-up test, following procedures outlined by the American College of Sports Medicine.
  • Low-back and abdominal endurance: Evaluated using an isometric side-bridge test. Time to exhaustion was computed for both left and right sides, and the average score was reported.
  • Low-back and hip flexibility: Evaluated via a standardized sit-and-reach test.
• Psychological Health Status:
  • Health-related Quality of Life (QoL): Assessed using the Medical Outcomes Trust Short-form 36 Health Status Questionnaire (SF36) Version 1.0. This is a widely used and validated questionnaire that assesses eight domains (e.g., physical functioning, bodily pain, mental health) and provides two summary scores (Physical Component Summary and Mental Component Summary).
  • State and Trait Anxiety: Assessed using the State-Trait Anxiety Inventory (STAI). This is a widely used and validated inventory consisting of two 20-item self-report scales. Scores range from 20 to 80, with lower scores indicating lower anxiety.
  • Job Satisfaction: Evaluated using the Job Descriptive Index (JDI) and the Job in General (JIG) scale. Both are validated for use in the general population, including office workers. The JDI assesses five specific perceptions of job satisfaction (supervision, co-workers, work, pay, and promotion), while the JIG assesses general job satisfaction.
• Demographics and Health Status: Collected at recruitment and baseline via standardized questionnaires and assessments, including age, occupation, height, weight, resting blood pressure, waist circumference, smoking history, medical history, and medication usage. Changes in health status and adverse events were monitored weekly via email questionnaires.

All HRV and musculoskeletal fitness assessments were performed by qualified and experienced personnel who were blinded to the participants' group assignments. Psychological questionnaires were self-administered.

This study employed a randomized controlled trial (RCT) design, which is considered the gold standard for evaluating the effectiveness of interventions. In an RCT, participants are randomly assigned to either an experimental group (receiving the intervention) or a control group (receiving no intervention or a placebo). This design is crucial because it aims to minimize bias and ensure that any observed differences between groups are due to the intervention itself, rather than other confounding factors.

Study Design and Duration:

• The trial compared outcomes of participants randomized to a hatha yoga experimental group with those assigned to a no-treatment control group.
• The intervention period lasted 10 weeks.
• Primary and secondary outcomes were collected at baseline (week 0) and following the intervention period (week 11).
• All data were collected between March and June 2011.

Randomization:

• Participants were randomized via computer-generated randomly permuted blocks stratified by gender. Stratification by gender ensures that an equal proportion of males and females are assigned to each group, which is important if gender might influence the outcomes. Computer-generated randomization helps prevent selection bias, where researchers might consciously or unconsciously assign certain participants to a particular group.
• An investigator not involved in data collection prepared the assignments in sealed envelopes, which were given to participants after baseline testing. This process further reduces potential bias in group assignment.

Blinding:

• Assessor blinding: Qualified and experienced personnel who assessed HRV and musculoskeletal fitness were blinded to the group assignment. This is a critical strength, as it prevents the assessors' expectations or biases from influencing the objective measurements. For example, an assessor who knows a participant is in the yoga group might inadvertently be more lenient on a push-up test or interpret HRV data differently.
• Participant and instructor blinding: Participants were aware of their group assignment (they knew if they were doing yoga or not), and the yoga instructor was obviously not blinded. This is common and often unavoidable in exercise interventions. The lack of participant blinding means that a placebo effect (improvements due to the expectation of benefit, rather than the intervention itself) cannot be ruled out for self-reported outcomes like psychological health.

Intervention Details:

• The experimental group completed a 10-week hatha yoga program, with three 50-minute sessions per week during lunch hour.
• Sessions were group-based and led by an experienced instructor.
• The program was designed for beginners, based on the Yoga Synergy Water Sequence, and involved approximately 95% asanas and vinyasa, including warm-ups, sun salutations, standing poses, floor postures, an inversion (shoulderstand), breathing exercises, and relaxation. Participants were instructed to choose appropriate difficulty levels.

Control Group:

• The control group was advised to maintain their current lifestyle practices and received no specific instructions or information about yoga. This "no-treatment" control allows for comparison against natural changes or the effects of time.

Statistical Approach:

• Analyses were performed using the Statistical Package for the Social Sciences (IBM©, SPSS Version 19.0).
• Data were inspected for normality (skewness and kurtosis between -1 and +1). Non-normally distributed data were log-transformed before analysis. (The abstract does not detail the specific statistical tests used, but typically, repeated measures ANOVA or ANCOVA would be used for pre-post comparisons between groups in an RCT).
• A post hoc analysis was conducted comparing participants who completed ≥70% of yoga sessions (n = 11, referred to as "high adherers") to the control group (n = 19). This type of analysis is exploratory and can generate hypotheses for future studies, but its findings are generally considered less robust than the primary analysis of the full experimental group because it breaks the original randomization.

What this design can and cannot prove:

• Can prove: The RCT design, with random assignment and assessor blinding for objective measures, provides strong evidence for a causal link between the yoga intervention and any observed changes in objective outcomes (like flexibility or muscular endurance) if the full experimental group showed significant differences compared to the control. For self-reported outcomes, the causal link is weaker due to the lack of participant blinding.
• Cannot prove:
  • Generalizability: The study was conducted on a relatively small, specific population (university office workers in Australia). The findings may not directly apply to other populations (e.g., different age groups, different occupations, individuals with higher stress levels or pre-existing conditions).
  • **Long-term effects