Distinct effects of aerobic exercise training and weight loss on glucose homeostasis in obese sedentary men

The decline in glucose homeostasis with aging may be due to the physical deconditioning and obesity that often develop with aging. The independent and combined effects of aerobic exercise training (AEX) and weight loss (WL) on glucose metabolism were studied in 47 nondiabetic sedentary older men. There were 14 men in a weekly behavioral modification/WL program, 10 in a 3 times/wk AEX program, 14 in an AEX+WL program, and 9 in the control (Con) group. The 10-mo intervention increased maximal oxygen consumption (V̇O(2max)) in both the AEX and AEX+WL groups [0.33 ± 0.05 and 0.37 ± 0.09 (SE) l/min, respectively], but V̇O(2max) did not significantly change in the WL (0.01 ± 0.06 l/min) and Con groups (-0.04 ± 0.05 l/min; P > 0.05). The AEX+WL and WL groups had comparable reductions in body weight (-8.5 ± 0.9 and -8.8 ± 1.2 kg, respectively) and percent fat (-5.5 ± 0.7 and -5.9 ± 1.1%, respectively) that were significantly greater than those in the Con and AEX groups. Oral glucose tolerance tests showed significant reductions in insulin responses in the AEX, WL, and AEX+WL groups, but the decrease in insulin response in the AEX+WL group was significantly greater than that in the other three groups. The glucose area decreased significantly in the WL and AEX+WL groups but did not change in the Con or AEX groups. There were significant increases in insulin-mediated glucose disposal rates as measured by the hyperinsulinemic (600 pmol · m^-2 · min^-1) euglycemic clamps in the AEX and AEX+WL groups [1.66 ± 0.50 and 1.76 ± 0.41 mg · kg fat-free mass (FFM)^-1 · min^-1, respectively] that were significantly greater than those in the WL (0.13 ± 0.31 mg · kg FFM^-1 · min^-1) and Con groups (- 0.05 ± 0.51 mg · kg FFM^-1 · min^-1; n = 5). These data suggest that AEX and WL improve glucose metabolism through different mechanisms and that the combined intervention of AEX+WL is necessary to improve both glucose tolerance and insulin sensitivity in older men.