<b>Objective:</b> Moderate-to-vigorous 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.
<p><b>Methods: </b>Baseline
7-day hip-worn accelerometry data from Look AHEAD participants (n=2,153, 57% women) were analyzed to identify
bout-related MVPA (≥3 metabolic
equivalent tasks (MET)/min
for ≥10mins). Cardiorespiratory fitness was assessed by maximal graded exercise
test. Participants were categorized into six groups based on the time of day
with the majority of bout-related MVPA (MET×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).
</p>
<p><b>Results:</b>
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 highest 4-year FRS (2.18% [0.70%, 3.65%]), but no association
was observed in women. </p>
<b>Conclusions:
</b>Timing of bout-related
MVPA is associated with<b> </b>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.