Can sedentary time attenuate the acute effect of exercise on insulin action?
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Impaired insulin action predicts the development of type 2 diabetes. Evidence is growing that sedentary time (SED) is a risk factor for morbidity and mortality, independent of moderate to vigorous physical activity (MVPA) levels. While it is clear from large-scale epidemiological studies that SED is associated with impaired insulin action, higher levels of evidence from intervention studies are sorely lacking. The objective of the present investigation was to determine whether a pragmatic 1 hour increase in daily SED for 4 days could mask the acute effect of exercise on insulin action. The study enrolled 15 sedentary, abdominally obese men and women. Participants completed 3 conditions, each of which was 4 days in length. A counterbalanced randomized crossover design was used, in which participants served as their own controls. In the baseline condition participants were instructed to maintain habitual levels of PA. In the exercise condition participants were asked to perform 1 hour of supervised moderate-to-vigorous exercise per day. In the exercise + sedentary condition participants completed 1 hour of moderate-to-vigorous exercise per day and were also asked to increase daily SED by 1 hour from baseline. PA and SED were assessed using accelerometry. Measurements of insulin action were obtained from an oral glucose tolerance test (OGTT) performed in the fasting state the morning after the 4 days of each condition. Unexpectedly, SED in the exercise condition decreased from baseline (9:28±0:45hr:min vs. 8:14±1:07hr:min, p<0.001), whereas SED was maintained at baseline levels in the exercise + sedentary condition. The exercise and exercise + sedentary conditions were therefore renamed as ‘exercise – sedentary’ and ‘exercise’, respectively. Insulin action was improved following the exercise – sedentary condition in comparison to baseline (1601±657pmol/L2h vs. 1181±419pmol/L2h, p<0.01). An improvement in insulin action was also observed in the exercise condition by comparison to baseline (1601±657pmol/L2h vs. 1362±456pmol/L2h, p<0.05). The improvement in insulin action following the exercise – sedentary condition in comparison to the exercise condition approached statistical significance but was not statistically significant (1362±456pmol/L2h vs. 1181±419pmol/L2h, p=0.058). These findings provide preliminary evidence in support of the notion that SED, in addition to the adoption of PA, may be an important behaviour to target for management of insulin action.