<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.
Reduced cardiorespiratory fitness, low physical activity and an urban environment are independently associated with increased cardiovascular risk in children
