Abstract
Introduction: Lifestyle interventions, with physical activity (PA) as a key component, are important to reducing cardiometabolic disease risk. In our work in both efficacy and effectiveness clinical trials, we have shown that season has a significant impact on subjectively determined moderate-vigorous (MV) PA levels, both at baseline and during the intervention. However, the effect of season in these lifestyle interventions has not yet been examined utilizing objective measurements of PA so that time spent in all PA intensities and sedentary behavior(SB) can be quantified. Hypothesis: Our hypothesis is that PA would increase and SB would decrease due to the intervention but that season would have an additional effect on both. Methods: We enrolled 150 overweight/obese adults (51.1±10.2 y; 79% Caucasian; 91% female) in a 12-month lifestyle intervention for weight loss that provided regular feedback to participants on diet and PA goal achievement. Six cohorts were recruited from 2012-2014. The PA goal was to achieve and maintain 150 minutes/week of MVPA. ActiGraph GT3x accelerometers, worn on the waist, were used to assess average daily step counts and time spent in PA and SB. Accelerometer recordings with 10 hours/day of wear time on ≥4 days were considered a valid assessment of typical PA and SB. Changes in activity variables at 6 months and 12 months were examined using linear mixed models. We also examined the season (winter, spring, summer, or autumn) when the intervention was implemented and if this affected changes in PA and SB. Results: Baseline accelerometer data were valid for 149 participants. Mean (SD) baseline values were 6132 (1873) steps counts/day, 11 (11) MVPA min/day, 245 (64) light intensity (L)PA min/day, 635 (85) SB min/day. Season was significantly related to step counts, LPA, MVPA, and SB with significantly lower PA and higher SB in the winter (p<0.05). Changes in LPA and SB were not significant over the entire follow-up (p>0.05). When adjusted (for monitor wear time/day and season) mean (SD) increases in step counts from baseline were 1128 (208) and 742(209) steps/day at 6 and 12 months, respectively (both p<0.0001). For MVPA adjusted mean (SD) increases from baseline were 7(1) and 6(1) min/day at 6 and 12 months, respectively (both p<0.0001). Conclusions: Relevant improvements in steps counts and MVPA were recorded at 6 and 12 months. This was true even after controlling for the effect of differences in the season of implementation. When considering the effect of lifestyle interventions on activity, future studies should consider the effect of seasonal changes on PA levels.
Published Version
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