Glucose tolerance and insulin sensitivity following exercise : influence of muscle mass and absolute work
To determine the influence of muscle mass and absolute work on glucose tolerance and insulin sensitivity following exercise, glucose and insulin responses to an oral glucose tolerance test (OGTT) were analyzed in twelve subjects at baseline and 16 to 18 hrs following three different exercise trials performed on a cycle ergometer: 1) two-legged exercise at 60% of two-leg maximal oxygen uptake (VO2max), 2) one-legged exercise at 60% of the oneleg VO2max, and 3) a second one-leg trial at 60% of one-leg VO2max with work matched to the work obtained during the two-leg trial. Each trial was preceeded by two days of inactivity and a three day diet replication. Analysis of serum glucose concentrations during the post-exercise OGTTs demonstrated that glucose tolerance was unaffected by either the amount of active tissue incorporated in the exercise and/or the amount of work completed by the active tissue. On the other hand, serum insulin concentrations following the two-leg trial decreased 23.5% from 347.62 ±37.98 to 266.05 :L41.62 gU/ml in comparison to the one-leg trial (p < 0.05). The incorporation of a smaller muscle mass which completed an equal amount of absolute work as the larger muscle mass (i.e. one-leg work matched trial) resulted in a large (19%), but nonsignificant reduction in the total insulin compared to the one-leg relative work trial. In addition, total insulin following the two-leg and the one-leg work matched trials were reduced by 19% and 14%, respectively, in comparison to baseline. However, they did not reach statistical significance. The results of this study indicate that the incorporation of a larger muscle mass during an acute bout of aerobic exercise results in a reduction in serum insulin in response to a post-exercise oral glucose challenge. In addition, increasing the absolute work of a muscle mass results in similar reductions in serum insulin regardless of the amount of muscle mass involved in the exercise. While glucose tolerance was unaltered by either the amount of active tissue and/or the amount of work completed by the active tissue.