Glucose clearance in aged trained skeletal muscle during maximal insulin with superimposed exercise

Insulin and muscle contractions are major stimuli for glucose uptake in skeletal muscle and have in young healthy people been shown to be additive. We studied the effect of superimposed exercise during a maximal insulin stimulus on glucose uptake and clearance in trained (T) (1-legged bicycle training, 30 min/day, 6 days/wk for 10 wk at ~70% of maximal O₂ uptake) and untrained (UT) legs of healthy men (H) [n = 6, age 60 ± 2 (SE) yr] and patients with Type 2 diabetes mellitus (DM) (n = 4, age 56 ± 3 yr) during a hyperinsulinemic (~16,000 pmol/l), isoglycemic clamp with a final 30 min of superimposed two-legged exercise at 70% of individual maximal heart rate. With superimposed exercise, leg glucose extraction decreased (P < 0.05), and leg blood flow and leg glucose clearance increased (P < 0.05), compared with hyperinsulinemia alone. During exercise, leg blood flow was similar in both groups of subjects and between T and UT legs, whereas glucose extraction was always higher (P < 0.05) in T compared with UT legs (15.8 ± 1.2 vs. 14.6 ± 1.8 and 11.9 ± 0.8 vs. 8.8 ± 1.8% for H and DM, respectively) and leg glucose clearance was higher in T (H: 73 ± 8, DM: 70 ± 10 ml. min^-1. kg leg^-1) compared with UT (H: 63 ± 8, DM: 45 ± 7 ml·min^-1 ·kg leg^-1) but not different between groups (P > 0.05). From these results it can be concluded that, in both diabetic and healthy aged muscle, exercise adds to a maximally insulin-stimulated glucose clearance and that glucose extraction and clearance are both enhanced by training.