Skeletal Muscle Metabolism during an Exercise Challenge pre and post Aerobic Training in Lean and Obese Middle-Aged Individuals

Abstract

PURPOSE: To examine the effects of exercise intensity (40 and 60% VO2peak) on skeletal muscle metabolism in sedentary middle-aged lean and obese individuals, pre and post an 8 week aerobic training program. METHODS: Ten normal weight (lean) and eight obese (age, 41.0 ± 2.2 and 39.3 ± 4.7 yrs; body mass index, 24.7 ±0.7 and 36.1 ± 2.0 kg/m2; VO2peak, 40.5 ± 2.3 and 36.6 ±1.5 ml/min/kg fat free mass) volunteers cycled for 10 min at 40% VO2peak and 10 min at 60% VO2peak pre and post 8 wk of exercise training (60 min/d, 5 d/wk, 60% VO2peak). Muscle biopsies were taken from the vastus lateralis muscle at rest and following 40 and 60% of pre-training VO2peak and blood samples were obtained throughout exercise both pre and post training. RESULTS: Aerobic training improved VO2peak by ∼24 and 17% in the obese and lean groups. Muscle citrate synthase activity was similar between groups before training and increased by ∼50% in each group post training (lean, 81.5 ± 8.0 to 122.8 ± 7.9 and obese, 77.8 ± 5.7 to 118.4 ± 3.2 mmol/min/kg dm). ±-hydroxyacyl-CoA-dehydrogenase activity was also similar between groups before training and increased by ∼40% following training in each group (lean, 44.4 ± 2.2 to 61.3 ± 5.4 and obese, 47.3 ± 3.3 to 65.5 ± 4.5 mmol/min/kg dm). Exercise increased venous plasma epinephrine and whole blood lactate (La) at 60% VO2peak in both groups, with 2–3 fold higher increases in the obese group. Post training, the exercise-induced epinephrine and La increases were blunted in both groups but to a greater extent in the obese. There were no differences between groups in resting muscle La, phosphocreatine (PCr), Cr or ATP contents pre or post training. Muscle La increased during exercise at 60% VO2peak in both groups with a greater response in the obese (23.4 ± 2.9 vs. 39.9 ± 4.7 mmol/kg dm). Following training, the muscle La increase was blunted in both groups but to a larger extent in the obese. Prior to training, exercise at both power outputs decreased muscle PCr similarly in lean and obese groups (lean, 86.2 ± 3.6 to 71.4 ± 4.8 and 53.6 ±4.9 mmol/kg dm at 40 and 60%; obese, 83.9 ± 3.9 to 69.4 ± 6.0 and 48.7 ± 4.9 mmol/kg dm at 40 and 60% VO2peak). Following training there was no significant decrease in PCr at either exercise intensity in both groups. Muscle ATP content was unaffected by exercise in either group both pre and post training. CONCLUSION: Prior to aerobic training, exercise at the same relative low and moderate intensities elicited a greater whole body and skeletal muscle metabolic response in middle-aged obese vs. lean individuals. In response to aerobic training, the metabolic responses to exercise at the same pre-training power output were blunted in both groups, but to a greater extent in the obese.