CHANGES IN INSULIN ACTION AND GLUT-4 WITH 6 DAYS OF INACTIVITY IN ENDURANCE RUNNERS

The purpose of this investigation was to determine whether decreased i nsulin action after 6 days of inactivity in endurance-trained runners was associated with a decrease in skeletal muscle glucose transporter protein levels (GLUT-4) in the gastrocnemius muscle. Seven endurance r unners (5 men and 2 women) volunteered to participate in this investig ation. All subjects had normal glucose tolerance as determined by the National Diabetes Data Group guidelines. Each individual completed two hyperinsulinemic euglycemic clamps at insulin infusion rates of 15 (L O) and 40 (HI) mU . m(-2). min(-1), one similar to 18 h after a traini ng bout and the second after 6 days of inactivity (IA)). Muscle biopsi es for the measurement of GLUT-4 were obtained from the gastrocnemius before each clamp. Glucose disposal rates during the last 30 min of ea ch insulin infusion were significantly reduced after 6 days of IA, ave raging 6.45 +/- 1.04 mg . kg fat-free mass (FFM)(-1). min(-1) before a nd 4.55 +/- 0.56 mg . kg FFM(-1). min(-1) after detraining for the LO insulin infusion rate and 13.77 +/- 0.88 mg . kg FFM(-1). min(-1) befo re and 11.81 +/- 0.60 mg . kg FFM(-1). min(-1) after detraining for th e HI insulin infusion rate (both P < 0.05), despite the fact that plas ma insulin was higher in the inactive state (LO, 19.2 +/- 0.9 mu U/ml before and 23.4 +/- 1.5 mu U/ml after detraining; HI, 56.0 +/- 2.0 mu U/ml before and 61.6 +/- 1.6 mu U/ml after detraining; P < 0.05)). Cal culated insulin clearance was greater in the trained than in the inact ive state (P < 0.03). Muscle GLUT-4 transporter protein after 6 days o f IA was reduced by 17.5 +/- 5.4% (P < 0.02). These results demonstrat e that 6 days of IA reduces insulin action in endurance-trained runner s and suggest that a reduction in muscle GLUT-4 transporter level play s a role in the decrease in glucose disposal rates.