Effect of Treadmill Training on Muscle Oxidative Capacity and Accretion in Young Male Obese and Nonobese Zucker Rats

This study was designed to determine if treadmill training of the male obese Zucker rat could reverse its deficit in muscle accretion, expose a possible latent defect in its muscle oxidative capacity or significantly alter its food intake and lipid deposition. At 12 wk of age muscle mass and myofibrillar protein concentration were significantly lower and body lipid and food intake were significantly higher in the sedentary obese than in the nonobese rat. Exercise, by both inducing hypophagia and increasing energy output, led to a lower body weight, body lipid, and muscle mass in the exercised than in the nonexercised rats. This response to exercise did not differ between both phenotypes, except for body lipid. In that case the reduction of body lipid was greater for the obese rats. Muscle mitochondrial enzyme activities and rates of mitochondrial respiration in the obese rats were not different or greater than those of their sedentary or pair-exercised nonobese counterparts. Taken together these data indicate that oxidative capacity per unit of muscle is not significantly lower in the obese rats than in nonobese rats in both sedentary and exercised states, but that total muscle oxidative capacity is lower on a whole-animal basis since total muscle mass is lower. Further, exercise reduces, but does not prevent the enhanced weight gain and lipid accretion that characterizes the obese rat.