Does Style Matter: Comparison of Moderate- to Low-intensity Styles of Yoga

This study investigates how two different styles of yoga, vinyasa yoga and gentle yoga, impact sleep and heart health in adults with and without insomnia. Insomnia, a common sleep disorder, increases the risk of heart disease, the leading cause of death worldwide. Recently, the American Heart Association identified poor sleep as a key factor in maintaining heart health, yet there is limited research on therapies that can simultaneously improve both sleep and cardiovascular function. By examining the immediate effects of a single evening session of yoga, this study aims to determine if yoga could serve as a practical, complementary approach to managing sleep and heart health.

Using a three-arm randomized crossover design, the study includes 42 participants, aged 18-40, who are either good sleepers or have diagnosed insomnia. Each participant will complete three sessions: one of vinyasa yoga, one of gentle yoga, and a non-active control session, with each session separated by a 72-hour washout period to avoid carryover effects. The yoga sessions will be standardized to 60 minutes and take place in the evening, approximately 4-6 hours before bedtime, under the supervision of a trained research staff.

The study has three main goals. First, examine whether different yoga styles influence heart function during sleep by measuring heart rate variability (HRV), a marker of nervous system balance that reflects the body's ability to regulate stress and relaxation. The investigators hypothesize that both yoga styles will improve HRV in people with insomnia more than in healthy sleepers. Second, to determine if vinyasa or gentle yoga improves sleep quality-measured by sleep efficiency (the percentage of time in bed spent asleep), total sleep time, and self-reported sleep quality-in adults with insomnia compared to those without sleep problems. Lastly, measure the impact of yoga on blood vessel function using flow-mediated dilation (FMD), a test that measures how well blood vessels expand in response to increased blood flow, with the expectation that vinyasa yoga's moderate intensity will provide greater immediate benefits compared to gentle yoga.

Inclusion criteria

• Adults 18-40 years
• Insufficiently inactive define by the L-CAT (responses below public health physical activity guidelines)
• Physical activity is not contraindicated (i.e., no affirmative responses on the Physical Activity Readiness Questionnaire for Everyone (PAR-Q+)
• Adults with diagnosed insomnia disorder and score ≥ 10 on the Insomnia Severity Index
• Good sleeps a score < 10 (no history of sleep disorder)
• Basic understanding of yoga poses
• Access to a smart device (such as a smartphone or tablet)

Exclusion criteria

• Regular yoga practice (> 60 minutes per week)
• Any diagnosed medical condition requiring medical clearance determined 'Yes' response on questions pertaining to a present medical condition(s) via PAR-Q+. This includes, but is not limited to, uncontrolled cardiovascular, metabolic, respiratory, musculoskeletal, neurological, or mental health conditions; recent stroke or concussion; active cancer treatment; and any combination of medical conditions that pose a health risk without physician supervision. All "yes" responses on the PAR-Q+ will be evaluated, and individuals requiring clearance will not be eligible to participate.
• Physical limitations and/or mobility restrictions (such as bone, joint, or soft tissue such as muscle, ligament, or tendon that could be made worse by becoming more physically active) via PAR-Q+
• Untreated major psychiatric disorders (e.g. major depression, bipolar disorder, schizophrenia)
• Elevated risk for sleep apnea (i.e., STOP-Bang score ≥ 5)
• Any other sleep disorders other than insomnia (e.g., sleep apnea, restless legs syndrome, circadian rhythm disorder, etc.)
• Current treatment for insomnia (e.g., hypnotic medications, cognitive behavioral therapy for insomnia, etc.)
• Current medications that affect heart or blood pressure (i.e., anti-depressants, beta-blockers, etc.)
• Current or planned pregnancy within the next 3 months
• Overnight shift work defined as regularly working anytime between 00:00 and 6:00am