Effects of Resistance-based Exercise Snacks With Varying Fragmentation Patterns on Lower Limb Function and Executive Cognition in Pre-frail Older Adults

This is a four-arm, parallel-group, randomized controlled pilot trial. Forty-eight to sixty community-dwelling pre-frail older adults (Fried frailty phenotype score 1-2, aged ≥70 years) will be randomly assigned to one of four groups (1:1:1:1 ratio). All groups perform a fixed total daily volume of 15 repetitions per exercise (sit-to-stand, squat, and heel raise), resulting in 45 total repetitions per day. The only difference between groups is the fragmentation pattern (i.e., repetitions per bout × bouts per day):

G1 (highly fragmented): 1 repetition of each exercise per bout, 15 bouts/day (~30 seconds per bout)

G2 (moderately fragmented): 3 repetitions of each exercise per bout, 5 bouts/day (~90 seconds per bout)

G3 (lowly fragmented): 5 repetitions of each exercise per bout, 3 bouts/day (~2.5 minutes per bout)

G4 (consecutive control): 15 repetitions of each exercise per bout, 1 bout/day (~7.5 minutes per bout)

The intervention period is 8 weeks. Outcomes are assessed at baseline, mid-intervention (week 4), and post-intervention (week 8). Primary outcomes include lower limb strength (30-second chair stand test) and dynamic balance (Timed Up and Go test). Secondary outcomes include comprehensive physical function (Short Physical Performance Battery), executive function (Stroop Color-Word Test and Trail Making Test), falls efficacy (modified Falls Efficacy Scale), adherence, acceptability, and adverse events.

Inclusion criteria

• 1. Age 65 years or older 2. Community-dwelling (living independently, not in a nursing home or long-term care facility) 3. Pre-frail status confirmed by Fried Frailty Phenotype score of 1-2 4. Mini-Mental State Examination (MMSE) score ≥24 5. Able to walk independently with or without a cane 6. No regular lower limb strength training (less than 2 times per week) in the past 3 months 7. Willing to adhere to the 8-week exercise intervention and complete all assessments 8. Provide written informed consent before any study-related procedures

Exclusion criteria

• 1. Lower limb fracture or joint replacement surgery within the past 6 months 2. Unstable angina or uncontrolled hypertension (resting systolic blood pressure ≥160 mmHg) 3. Severe osteoporosis (T-score <-2.5 with history of fragility fracture) 4. Neurological disorders affecting motor function (e.g., Parkinson's disease, post-stroke hemiplegia) 5. Severe cognitive impairment (MMSE score <24) 6. Unstable cardiac or pulmonary disease (e.g., recent myocardial infarction, severe COPD exacerbation) 7. Severe visual or hearing impairment that limits ability to follow instructions or perform exercises safely 8. Participation in another interventional clinical trial within the past 30 days 9. Any other medical or psychological condition that, in the opinion of the principal investigator, would compromise participant safety or study adherence