In the present short review some factors affecting glucose utilization during exercise in skeletal muscle will be briefly described. Special focus will be put on the glucose transport step across the sarcolemma. Glucose transporters (GLUT4) are expressed at a surprisingly similar level in the different muscle fiber types in human skeletal muscle in contrast to findings in the rat. When working at the same absolute work load muscle glucose transport is decreased in trained compared with untrained muscle in part due to a decrease in GLUT4 translocation to the sarcolemma in trained muscle. However, when trained and untrained muscle are stressed severely by a workload taxing 100% of their peak oxygen uptake in a glycogen-depleted state, then glucose uptake is larger in trained than in untrained muscle and correlates with muscle GLUT4 content. Finally, the possible role of the AMP-activated protein kinase (AMPK) in regulating glucose uptake during exercise is discussed. It is indicated that at present no experiments definitively link activation of AMPK to activation of muscle glucose transport during exercise.
The authors are with the Copenhagen Muscle Research Centre in the Department of Human Physiology at the University of Copenhagen, 13 Universitetsparken, DK-2100 Copenhagen, Denmark. W. Derave is presently with the Faculty of Physical Education and Physiotherapy, Exercise Physiology and Biomechanics Laboratory, Catholic University of Leuven, B-3001 Heverlee, Belgium.