Adverse Events during a 12-Month Multisite Dose–Response Aerobic Exercise Intervention

Introduction This study aimed to assess the incidence of adverse events (AE) in older adults participating in a yearlong exercise intervention, investigate potential dose–response relationships between exercise duration and AE frequency, and identify demographic factors associated with AE risk. Methods A total of 648 older adults were randomized into one of three exercise groups: low-intensity stretching and toning (S&T), 150 min of aerobic exercise per week (150Ex), or 225 min of aerobic exercise per week (225Ex). Adverse events were tracked during the intervention, with event rates calculated based on participant adherence and time in the study. Generalized linear models were employed to compare AE incidence across groups. Post hoc comparisons were used to calculate incidence rate ratios (IRR) for AE between groups, adjusting for multiple comparisons. Results Overall, 306 AEs were reported, with 44% related to the intervention. No significant dose–response relationship was observed for all-cause AE between groups. However, intervention-related AEs were more frequent in the aerobic exercise groups. Participants in the 150Ex group had a 77% higher rate of intervention-related AE than the S&T group, and the 225Ex group had an 88% higher rate than the S&T group. Higher adherence was associated with fewer all-cause AE, and greater comorbid burden was associated with more AE. Conclusions Although aerobic exercise increased the risk of intervention-related AE, the overall risk of all-cause AE was not found to be different across exercise intensities. Higher adherence to the exercise regimen was associated with fewer AE. These findings suggest that aerobic exercise is generally safe in older adults, with the benefits outweighing the risks.