Device-Measured Baseline Physical Activity Modifies 24-h CGM Glycemic Responses and 12- Week Time-in-Range After Mixed Exercise Training in Type 2 Diabetes

Purpose To evaluate whether baseline habitual physical activity (PA), modeled as continuous moderate-to-vigorous PA (MVPA), modifies acute glycemic responses to different exercise modalities, and whether acute response is associated with 12-week glycemic status in older adults with type 2 diabetes. Methods 23 participants completed a randomized crossover acute phase (aerobic, resistance, mixed) and then a 12-week free-living mixed-exercise program (n = 22). Continuous glucose monitoring quantified time in range (TIR, 3.9–10.0 mmol/L). Acute responses were analyzed using linear mixed models including modality, baseline MVPA, and modality × MVPA interaction terms, adjusted for age and sex. Associations between acute 24-h TIR after the mixed session and 12-week mean TIR were tested using Pearson correlation and HbA1c-adjusted partial correlation; stability was evaluated with leave-one-out cross-validation (LOOCV). Adherence interaction analyses were exploratory. Results Evidence for effect modification by baseline MVPA in the acute phase was limited (Mixed × MVPA: β = -0.263, 95% CI -0.585 to 0.058; P = 0.109). Acute 24-h TIR after mixed exercise was strongly associated with 12-week mean TIR (r = 0.887; partial r = 0.815; both P < 0.001), with stable LOOCV performance (R² = 0.729). Exploratory analyses suggested a baseline MVPA × adherence interaction for long-term TIR (β = 0.69; P = 0.031). Conclusion Acute CGM response was strongly associated with longer-term glycemic status, whereas acute interaction evidence by baseline MVPA was not definitive. A short CGM-based exercise challenge may support response stratification, pending external validation.