Aquatic Power Training Dosing Strategies and Creatine Supplementation in Older Adults

This randomized controlled trial will investigate the effects of different aquatic power training dosing strategies and creatine supplementation on functional and multisystem adaptations in community-dwelling older adults. Participants will be randomly allocated to one of five parallel groups: (1) aquatic power training regulated according to rating of perceived exertion during the first repetition (RPE-1) plus placebo; (2) aquatic power training using a conventional time-based dosing strategy plus placebo; (3) time-based aquatic power training plus creatine supplementation; (4) sedentary control plus placebo; or (5) sedentary control plus creatine supplementation. The intervention will last 16 weeks. Aquatic training will be performed three times per week for approximately 60 minutes per session. Participants allocated to creatine supplementation will receive 3 g/day of creatine monohydrate, whereas the corresponding placebo groups will receive a visually indistinguishable placebo following the same supplementation schedule. The primary outcomes will assess body composition, muscle strength, and functional capacity. Additional outcomes will examine bone health, cardiometabolic health, inflammatory and oxidative stress biomarkers, immune function, neurobiological and cognitive function, quality of life, sleep quality, psychological status, fatigue, and affective state. Assessments will be performed before and after the 16-week intervention.

Inclusion Criteria: 1. Age ≥60 years at enrollment. 2. Community-dwelling and functionally independent in basic activities of daily living. 3. Able to ambulate independently, with or without usual assistive devices, and able to safely perform the physical assessments included in the study. 4. Clinically stable; participants with chronic diseases must have maintained stable pharmacological treatment for at least three months before the intervention. 5. Not currently participating in a structured moderate- or high-intensity strength or power training program or another systematic supervised exercise program. 6. Available and willing to participate throughout the 16-week intervention and complete all scheduled assessments. 7. Willing to accept random allocation to any study group and creatine or placebo supplementation when applicable. 8. Willing to maintain stable dietary habits throughout the intervention. 9. Able and willing to provide written informed consent Exclusion Criteria: 1. Uncontrolled cardiovascular, respiratory, metabolic, neurological, or musculoskeletal disease contraindicating exercise or limiting safe participation. 2. Unfavorable medical assessment for participation in supervised exercise. 3. Uncontrolled hypertension at screening. 4. Known kidney disease, renal failure, or clinically relevant impairment of renal function. 5. Active liver disease or clinically relevant impairment of liver function. 6. Active malignant neoplasm or current cancer treatment. 7. Endocrine or metabolic disorders considered by the research team to substantially interfere with the study's primary outcomes. 8. Current use, or use during the previous three months, of creatine or other supplements with potential ergogenic or anabolic effects. 9. Pharmacological treatment considered likely to substantially modify the study's primary outcomes. 10. Participation during the previous three months in a systematic moderate- or high-intensity strength or power training program.