Skeletal muscle function and metabolism in obese women

A possible mechanism to regulate body weight during a high calorie intake may be an increased metabolic rate in skeletal muscle. To approach this hypothesis the energy metabolites, ATP, phosphocreatine, creatine, glycogen and lactate were measured in biopsies from the quadriceps femoris muscle. Concomitantly the function of the adductor pollicis muscle was studied as assessed after electrical stimulation of the ulnar nerve. The muscle function variables were, force of contraction at 5, 10, 20, and 50 Hz of stimulation, relaxation rate, and endurance. Eight obese women were studied before gastroplastic surgery and 6 months postoperatively and a weight loss of 19.4 +/- 3.4% (mean +/- SEM). Preoperatively ATP, phosphocreatine, glycogen, and lactate were significantly decreased and the same pattern was found postoperatively. These findings can be related to a low production of energy-rich phosphates or a high energy utilization. Both pre- and postoperatively there was, a decreased force of contraction at 10 Hz of stimulation (p less than 0.001), a faster relaxation rate (p less than 0.01) and a normal endurance. These functional results indicate a high metabolic rate. At admission a decreased serum insulin level indicated a moderate insulin resistance which was normalized after the weight loss. The triiodothyronine concentration was normal before and after operation. In conclusion our findings of changed muscle energy metabolite concentrations and altered muscle function indicate a high metabolic rate in skeletal muscle in obese women. This may be an adaptation in skeletal muscle energy metabolism to a high body weight.