Although detrimental associations of sitting time and health indicators have been observed in young adults, evidence of pathophysiological mechanisms is lacking. Therefore, this study tested the hypothesis that the acute cardiometabolic effects of prolonged sitting can be compensated by hourly interruptions to sitting in healthy, young adults. Additionally, leg muscle activation during sitting and moderate-intensity physical activity interruptions was assessed. Eleven apparently healthy adults (18-24 yr; five men/six women) participated in this randomized, crossover study, involving two experimental conditions: 1) 8 h prolonged sitting and 2) 8 h of sitting, interrupted with hourly, 8-min, moderate-intensity cycling exercise bouts. In both conditions, participants consumed two standardized, high-fat mixed meals after 1 and 5 h. Capillary blood samples were collected hourly during each 8-h experimental condition. Muscle activity was measured using electromyography. Muscle activity during cycling was seven to eight times higher compared with rest. Postprandial levels of C-peptide were significantly lower (unstandardized regression coefficient = -0.19; confidence interval = [-0.35; -0.03]; P = 0.017) during interrupted sitting compared with prolonged sitting. Postprandial levels of other cardiometabolic biomarkers (e.g., glucose, triglycerides, cholesterol) were not significantly different between conditions. Hourly physical activity interruptions in sitting time, requiring a muscle activity of seven to eight times the resting value, led to an attenuation of postprandial C-peptide levels but not for other cardiometabolic biomarkers compared with prolonged sitting in healthy, young adults. Whether this acute effect transfers to chronic effects over time is unknown.
Keywords: cardiometabolic risk; interrupted sitting; prolonged sitting; sedentary behavior.