EFFECT OF 7-10 DAYS OF CYCLE ERGOMETER EXERCISE ON SKELETAL-MUSCLE GLUT-4 PROTEIN-CONTENT

Previous studies in animals and humans have shown that endurance exerc ise-training protocols of several weeks to many months in duration ind uce adaptive increases in skeletal muscle GLUT-4 protein concentration . It is generally assumed that the increase in GLUT-4 concentration is a long-term adaptation to training. The present study examined whethe r 7-10 days of cycle ergometer exercise could induce increases in skel etal muscle GLUT-C levels. Eight healthy subjects (4 men, 4 women) age d 31 +/- 2 (SE) yr exercised 2 h daily at 65-70% of peak O-2 uptake (V O2peak) for either 7 (n = 3) or 10 (n = 5) consecutive days. Muscle bi opsies (vastus lateralis) were obtained before initiation of the exerc ise program and 36-48 h after the final bout of exercise. Glucose tran sporter protein was quantitated by Western blotting using antiserum sp ecific for GLUT-4. VO2peak was increased by 10% (from 3.0 +/- 0.2 to 3 .3 +/- 0.2 l/min; P < 0.01) in response to the training. Body weight d id not change (74.3 +/- 4.6 before vs. 75.0 +/- 4.2 kg after) as a res ult of training. Muscle GLUT-4 immunoreactivity was increased 98% (fro m 584 +/- 50 to 1,154 +/- 40 counts per minute I-125/25 mu g protein; P < 0.001) in response to training. Increases in VO2peak and GLUT-4 pr otein were similar for 7 and 10 days of training. These results sugges t that, given an adequate training stimulus, adaptations in skeletal m uscle GLUT-4 protein occur very rapidly. Furthermore, the increase in GLUT-4 after 7-10 days of exercise is as large as that reported in stu dies employing long-term training protocols.