Effect of aging on response to exercise training in humans: skeletal muscle GLUT-4 and insulin sensitivity

The purpose of this study was to compare the effects of short-term exercise training on insulin-responsive glucose transporter (GLUT-4) concentration and insulin sensitivity in young and older individuals. Young and older women [22.4 +/- 0.8 (SE) yr, n = 9; and 60.9 +/- 1.0 yr, n = 10] and men (20.9 +/- 0.9, n = 9; 56.5 +/- 1.9 yr, n = 8), respectively, were studied before and after 7 consecutive days of exercise training (1 h/day, approximate to 75% maximal oxygen uptake). The older groups had more adipose tissue, increased central adiposity, and a lower maximal oxygen uptake. Despite these differences, increases in whole body insulin action (insulin sensitivity index, determined with an intravenous glucose tolerance test and minimal-model analysis) with training were similar regardless of age, in both the women and men (mean increase of 2.2 +/- 0.3-fold). This was accompanied by similar relative increases in muscle (vastus lateralis) GLUT-4 protein concentration, irrespective of age (mean increase of 3.1 +/- 0.7-fold). Body mass did not change with training in any of the groups. These data suggest that older human skeletal muscle retains the ability to rapidly increase muscle GLUT-4 and improve insulin action with endurance training.