Adverse Events During a 12-month Multi-Site and Dose-Response Aerobic Exercise Intervention

Purpose: This study aimed to assess the incidence of adverse events (AE) in older adults participating in a year-long exercise intervention, investigating potential dose-response relationships between exercise intensity and AE frequency, and identifying 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 minutes of aerobic exercise per week (150Ex), or 225 minutes 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 (IRRs) for AE between groups, adjusting for multiple comparisons. Results: Overall, 306 AE were reported, with 44% related to the intervention. No significant dose-response relationship was observed for all-cause AE between groups. However, intervention-related AE were more frequent in the aerobic exercise groups. Participants in the 150Ex group had a 77% higher rate of intervention-related AE compared to the S&T group, and the 225Ex group had an 88% higher rate. Higher adherence was associated with fewer all-cause AE, and greater comorbid burden was associated with more AE. Conclusions: While aerobic exercise increased the risk of intervention-related AE, the overall risk remained low. Higher adherence to the exercise regimen was associated with fewer AE. These findings suggest aerobic exercise is generally safe in older adults, with the benefits outweighing the risks.