Aerobic exercise plus weight loss improves insulin sensitivity and increases skeletal muscle glycogen synthase activity in older men.

The purpose of this study was to determine the effects of 6-month aerobic exercise training + weight loss (AEX + WL) on basal and insulin activation of glycogen synthase, basal citrate synthase activity, and Akt and AS160 phosphorylation in older, overweight/obese insulin-resistant men (n = 14; 63 ± 2 years; body mass index, 32 ± kg/m(2)). Muscle samples of the vastus lateralis were collected before and during a 3-hour 80 mU/m(2)/min hyperinsulinemic-euglycemic clamp. AEX + WL increased VO2max by 11% (p < .05) and decreased body weight (-9%, p < .001). AEX + WL increased basal citrate synthase activity by 46% (p < .01) and insulin activation of independent (2.9-fold) and fractional (2.3-fold) activities (both p < .001) of glycogen synthase. AEX + WL had no effect on phosphorylation of Akt or AS160. Glucose utilization (M) improved 25% (p < .01), and the change tended to be related to the increase in insulin activation of glycogen synthase fractional activity (r = .50, p = .08) following AEX + WL. In summary, AEX + WL has a robust effect on insulin activation of skeletal muscle glycogen synthase activity that likely contributes to improved glucose utilization in older insulin-resistant men.