Sarcolemmal glucose transport and GLUT-4 translocation during exercise are diminished by endurance training

Glucose utilization during exercise of a given submaximal power output is decreased after endurance training. The aim of the present study was to elucidate the mechanisms behind this phenomenon by utilizing the sarcolemmal giant vesicle technique. Eight healthy young untrained men endurance trained one thigh for 3 wk. They then exercised both thighs simultaneously at the same work load (77% of peak O2 uptake of the untrained thigh) for 40 min. Training increased muscle GLUT-4 protein by 70% (P < 0.05). Glucose uptake during exercise was 38% lower (P < 0.05) in the trained (T) thigh than in the untrained (UT) thigh because of both a lower (P < 0.05) glucose extraction and blood flow in T. During exercise, sarcolemmal GLUT-4 protein content and glucose transport capacity increased significantly less in T than in UT muscle, and muscle glucose concentration was lower in T compared with UT (P < 0.05) at the end of exercise. It is concluded that, despite a large increase in muscle GLUT-4 with endurance training, exercise of a given submaximal power output increases muscle glucose uptake less in T than in UT muscle. It is suggested that the mechanism behind this phenomenon is blunted exercise-induced translocation of GLUT-4 to the sarcolemma, resulting in a blunted increase in sarcolemmal glucose transport in T muscle.