The Effects of a 6-Month Intervention Aimed to Reduce Sedentary Time on Skeletal Muscle Insulin Sensitivity - A Randomized Controlled Trial.

Sedentary behavior (SB) and physical inactivity associate with impaired insulin sensitivity. We investigated whether an intervention aimed at a 1h reduction in daily SB during 6 months would improve insulin sensitivity in the weight-bearing thigh muscles. Forty-four sedentary inactive adults [mean age 58 (SD 7) years; 43% men] with metabolic syndrome were randomized into intervention and control groups. The individualized behavioral intervention was supported by an interactive accelerometer and a mobile application. SB, measured with hip-worn accelerometers in 6-s intervals throughout the 6-month intervention, decreased by 51 (95%CI 22-80) min/day and physical activity (PA) increased by 37 (95%CI 18-55) min/day in the intervention group with non-significant changes in these outcomes in the control group. Insulin sensitivity in the whole body and in the quadriceps femoris and hamstring muscles, measured with hyperinsulinemic euglycemic clamp combined with [18F]fluoro-deoxy-glucose PET, did not significantly change during the intervention in either group. However, the changes in hamstring and whole-body insulin sensitivity correlated inversely with the change in SB and positively with the changes in moderate-to-vigorous PA and daily steps. In conclusion, these results suggest that the more the participants were able to reduce their SB, the more their individual insulin sensitivity increased in the whole body and in the hamstring muscles, but not in quadriceps femoris. However, according to our primary RCT results, this kind of behavioral interventions targeted to reduce sedentariness may not be effective in increasing skeletal muscle and whole-body insulin sensitivity in people with metabolic syndrome at the population level.