Few studies have compared the relative benefits of moderate- versus higher intensity exercise training on improving insulin sensitivity in older people while holding exercise volume constant. Healthy older (73 +/- 10 yr) women (N = 25) who were inactive, but not obese, were randomized into one of three training programs (9-mo duration): (1) high-intensity (80% peak aerobic capacity (VO2peak); TH) aerobic training; (2) moderate-intensity (65% VO2peak; TM) aerobic training; or (3) low-intensity (stretching) placebo control (50% VO2peak; CTB). Importantly, exercise volume (300 kcal/session) was held constant for subjects in both the TH and the TM groups. VO2peak was determined by using a graded exercise challenge on a treadmill. Total body fat and lean mass were determined with dual-energy x-ray absorptiometry. The rate of insulin-stimulated glucose utilization as well as the suppression of lipolysis were determined approximately 72 h after the final exercise bout by using a two-step euglycemic-hyperinsulinemic clamp. We observed improved glucose utilization at the higher insulin dose with training, but these improvements were statistically significant only in the TH (21%; p = 0.02) compared with the TM (16%; p = 0.17) and CTB (8%; p = 0.37) groups and were observed without changes in either body composition or VO2peak. Likewise in the TH group, we detected a significant improvement in insulin-stimulated suppression (%) of adipose tissue lipolysis at the low-insulin dose (38 to 55%, p < 0.05). Our findings suggest that long-term higher intensity exercise training provides more enduring benefits to insulin action compared with moderate- or low-intensity exercise, likely due to greater transient effects.

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