Tai Chi Intervention for Balance Function in Older Adults: Predictive and Modifying Roles of Circadian Age

BACKGROUND AND RATIONALE Falls are a leading cause of injury and disability in older adults, and balance dysfunction is a key modifiable risk factor. Tai Chi, a traditional Chinese mind-body exercise, has been shown to improve balance, reduce fall risk, and benefit cognitive health in older populations. However, individual variability in response to Tai Chi remains poorly understood, and the biological mechanisms underlying its benefits are incompletely characterized.

Circadian rhythm disruption has emerged as a hallmark of biological aging. The investigators have developed and validated a circadian age (CircAge) assessment system based on the UK Biobank cohort (N\>90,000), which independently predicts mortality risk. Whether individuals with accelerated circadian aging benefit more from Tai Chi intervention is unknown. This trial addresses this gap by integrating circadian age assessment with multi-modal outcome evaluations.

OBJECTIVES The primary objective is to evaluate the effect of a 12-week Tai Chi intervention on balance function in community-dwelling older adults. Secondary objectives are to assess effects on physical function, psychological health, cognitive function, and sleep quality. Exploratory objectives are to examine the predictive and modifying roles of baseline circadian age acceleration on intervention outcomes.

STUDY DESIGN This is a two-arm parallel, single-blind (assessor-blinded) randomized controlled trial. Ninety community-dwelling older adults are randomly allocated 1:1 to a Tai Chi group or a health education control group. Randomization is computer-generated using variable block sizes, stratified by sex and baseline Berg Balance Scale score (≤45 vs \>45). Allocation concealment is maintained via sequentially numbered opaque sealed envelopes. Outcome assessors are blinded to group allocation. After the 12-week intervention, the control group is offered free Tai Chi classes to ensure ethical equipoise.

ASSESSMENT SCHEDULE Wrist-worn accelerometer (ActiGraph) recordings are collected at baseline over 7 consecutive days for circadian age computation. All baseline accelerometer recordings are completed prior to randomization. Full outcome assessments are conducted at baseline (week 0) and at the end of intervention (week 12). A streamlined midpoint assessment (week 6) includes only the Berg Balance Scale and Timed Up and Go test. Fasting blood samples for routine clinical chemistry are collected at week 0 and week 12.

STATISTICAL ANALYSIS A sample size of 90 (45 per group) provides \>80% power to detect a standardized effect size of d=0.50 in Berg Balance Scale change at week 12, assuming α=0.05 (two-sided) and 20% attrition. The primary analysis follows the intention-to-treat principle using linear mixed-effects models adjusted for baseline score, age, sex, and circadian age acceleration, with class as a random effect for the Tai Chi group. Exploratory analyses include circadian age × group interaction terms.

LONG-TERM FOLLOW-UP After the 12-week intervention, participants are invited to enter a long-term health database with periodic follow-ups tracking balance function, fall events, and overall health status.

• Change in Timed Up and Go (TUG) Test [Time frame: Change from baseline to end of intervention, up to 12 weeks]
• Change in Grip Strength [Time frame: Change from baseline to end of intervention, up to 12 weeks]
• Change in Balance Performance Measured by InBody Balance Trainer [Time frame: Change from baseline to end of intervention, up to 12 weeks]
• Change in Single-Leg Eye-Closed Standing Time [Time frame: Change from baseline to end of intervention, up to 12 weeks]
• Change in Vertical Jump Height [Time frame: Change from baseline to end of intervention, up to 12 weeks]
• Change in Reaction Time [Time frame: Change from baseline to end of intervention, up to 12 weeks]
• Change in Activities-Specific Balance Confidence (ABC) Scale [Time frame: Change from baseline to end of intervention, up to 12 weeks]
• Change in Geriatric Depression Scale (GDS-15) Score [Time frame: Change from baseline to end of intervention, up to 12 weeks]
• Change in Generalized Anxiety Disorder Scale (GAD-7) Score [Time frame: Change from baseline to end of intervention, up to 12 weeks]
• Change in Shape Trail Test (STT) Part A and Part B Completion Time [Time frame: Change from baseline to end of intervention, up to 12 weeks]
• Change in Pittsburgh Sleep Quality Index (PSQI) Score [Time frame: Change from baseline to end of intervention, up to 12 weeks]