Acute exercise induces GLUT4 translocation in skeletal muscle of normal human subjects and subjects with type 2 diabetes.

Total GLUT4 content in skeletal muscle from individuals with type 2 diabetes is normal; however, recent studies have demonstrated that translocation of GLUT4 to the plasma membrane is decreased in response to insulin stimulation. It is not known whether physical exercise stimulates GLUT4 translocation in skeletal muscle of individuals with type 2 diabetes. Five subjects (two men, three women) with type 2 diabetes and five normal control subjects (5 men), as determined by a standard 75-g oral glucose tolerance test, were recruited to determine whether an acute bout of cycle exercise activates the translocation of GLUT4 to the plasma membrane in skeletal muscle. Each subject had two open biopsies of vastus lateralis muscle; one at rest and one 3-6 weeks later from the opposite leg after 45-60 min of cycle exercise at 60-70% of VO2max. Skeletal muscle plasma membranes were prepared by subcellular fractionation, and GLUT4 content was determined by Western blotting. Plasma membrane GLUT4 increased in each subject in response to exercise. The mean increase in plasma membrane GLUT4 for the subjects with type 2 diabetes was 74 +/-20% above resting values, and for the normal subjects the increase was 71+/-18% above resting values. Although plasma membrane GLUT4 content was approximately 32% lower at rest and after exercise in the muscle of the subjects with type 2 diabetes, the differences were not statistically significant. We conclude that in contrast to the previously reported defect in insulin-stimulated GLUT4 translocation in skeletal muscle of individuals with type 2 diabetes, a single bout of exercise results in the translocation of GLUT4 to the plasma membrane in skeletal muscle of individuals with type 2 diabetes. These data provide the first direct evidence that GLUT4 translocation is an important cellular mechanism through which exercise enhances skeletal muscle glucose uptake in individuals with type 2 diabetes.

Effect of weight loss and refeeding diet composition on anaerobic performance in wrestlers.

Collegiate wrestlers (N = 12) consumed a formula, hypoenergy diet (18 kcal.kg-1, 60% carbohydrate) without dehydration for 72 h. For the next 5 h, the athletes were fed either a 75% (HC) or a 47% (MC) carbohydrate formula diet of 21 kcal.kg-1. Each wrestler performed three anaerobic arm ergometer performance tests (TEST1, before weight loss; TEST2, after weight loss; TEST3, after refeeding). Blood withdrawn just before and after each test was analyzed for pH, bicarbonate, base excess, glucose, and lactate. Both groups had a similar significant reduction in total work done during TEST2 (92.4% of TEST1). Work done in TEST3 by HC was 99.1% of TEST1 while MC did 91.5% of their initial work (P = 0.1). Peak power was unaffected by the treatment. Plasma lactate significantly increased during the performance test from 1.72 to 21.91 mmol.l-1 as did plasma glucose from 4.88 to 5.25 mmol.l-1 when groups and trials were collapsed. Lactate accumulation was diminished during TEST2 compared with the other tests. Although the exercise bout reduced pH, bicarbonate, and base excess, there was no difference in the effect by group. In conclusion, weight loss by energy restriction significantly reduced anaerobic performance of wrestlers. Those on a high carbohydrate refeeding diet tended to recover their performance while those on a moderate carbohydrate diet did not. The changes in performance were not explained by the acid/base parameters measured.