Does Age Moderate Metabolic and Hormonal Adaptations to Resistance Training in Overweight Female Athletes? A Study Protocol for a Prospective, Age-Stratified Randomized Controlled Trial

Background: A recently completed 12-week randomized controlled trial (RCT) of resistance training (RT) in overweight female university athletes in China found, in exploratory regression analysis, that age — not baseline BMI — significantly predicted the magnitude of insulin-sensitivity improvement (B = 0.085, t = 2.127, p = 0.036). That trial was neither designed nor powered to test age as a moderator, so the finding is hypothesis-generating rather than confirmatory. Methods: This protocol specifies a prospective, parallel-group, age-stratified RCT. Overweight (BMI ≥ 25 kg/m²) female athletes aged 18–45 years will be stratified into Younger (18–29) and Older (30–45) cohorts before 1:1 randomization to RT or non-exercise control within each stratum. The RT protocol replicates the supervised, periodized 12-week program used in the index trial. Primary analysis: moderated multiple regression (Age × Group interaction) on ΔHOMA-IR; secondary: bootstrapped mediation analysis with Δcortisol as mediator. Results: Trial status: protocol stage. No participants have yet been recruited and no empirical results are reported in this manuscript; the target enrollment is 135 participants (≈34 per cell), calculated a priori for the primary moderated-regression test (α = .05, power = .80, f² = 0.10). Conclusion: This will be the first purpose-built, adequately powered trial testing age as a moderator of metabolic and hormonal adaptation to RT in this population. Institutional ethics approval and prospective public trial registration are required before recruitment begins; neither has yet been sought.