Timing of Resistance Exercise and Cardiometabolic Outcomes in Adults with Prediabetes: A Secondary Analysis

Objective: The objective of this study was to explore if the time of day (AM vs PM) resistance exercise is performed influences glucose and insulin concentrations, body composition, and muscular strength in adults with prediabetes. Methods: A secondary data analysis was conducted using data from the "Resist Diabetes" study, a phase II exercise intervention. Participants (Age:59.9±5.4 yrs; BMI:33±3.7 kg/m²) with prediabetes and overweight or obesity were categorized into AM (N=73) or PM (N=80) exercisers based on when they completed all of their supervised exercise sessions during a 12-week, 2x/week resistance exercise intervention. Blood glucose and insulin derived from oral glucose tolerance tests, body composition, and muscular strength were assessed pre and post resistance exercise training. Inverse propensity score weighting approach was used to estimate the efficacy of AM/PM exercise on the change of clinical responses. Paired samples t-test was used to compare pre-/post outcomes within AM/PM group. Results: No differences between AM and PM exercisers were detected in the change in glucose or insulin areas under the curve (AUC), body composition, or muscular strength. When exploring within-group changes, PM exercisers reduced glucose AUC (change: -800.6 mg/dl*120 min; p=0.01), whereas no significant change was detected for AM exercisers (change: -426.9 mg/dl*120 min; p=0.26). Only AM exercisers increased fat-free mass (change: 0.6 kg; p=0.001). Conclusions: The time of day of resistance exercise is performed may have some impact on glucose concentrations and body composition response. Future randomized clinical trials are needed to understand how exercise timing influences cardiometabolic outcomes in at-risk adults.