OBJECTIVE Moderate- to vigorous-intensity physical activity (MVPA) improves cardiovascular health. Few studies have examined MVPA timing. We examined the associations of timing of bout-related MVPA with cardiorespiratory fitness and cardiovascular risk in adults with type 2 diabetes.

RESEARCH DESIGN AND METHODS Baseline 7-day hip-worn accelerometry data from Look AHEAD participants (n = 2,153, 57% women) were analyzed to identify bout-related MVPA (≥3 METs/min for ≥10 min). Cardiorespiratory fitness was assessed by maximal graded exercise test. Participants were categorized into six groups on the basis of the time of day with the majority of bout-related MVPA (METs × min): ≥50% of bout-related MVPA during the same time window (morning, midday, afternoon, or evening), <50% bout-related MVPA in any time category (mixed; the reference group), and ≤1 day with bout-related MVPA per week (inactive).

RESULTS Cardiorespiratory fitness was highly associated with timing of bout-related MVPA (P = 0.0005), independent of weekly bout-related MVPA volume and intensity. Importantly, this association varied by sex (P = 0.02). In men, the midday group had the lowest fitness (β = −0.46 [95% CI −0.87, −0.06]), while the mixed group in women was the least fit. Framingham risk score (FRS) was associated with timing of bout-related MVPA (P = 0.02), which also differed by sex (P = 0.0007). The male morning group had the highest 4-year FRS (2.18% [0.70, 3.65]), but no association was observed in women.

CONCLUSIONS Timing of bout-related MVPA is associated with cardiorespiratory fitness and cardiovascular risk in men with type 2 diabetes, independent of bout-related MVPA volume and intensity. Prospective studies are needed to determine the impacts of MVPA timing on cardiovascular health.