Few studies have compared the relative benefits of moderate- vs. 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 (V(O2)peak); T(H)] aerobic training; 2) moderate-intensity (65% V(O2)peak; T(M)) aerobic training; or 3) low-intensity (stretching) placebo control (50% V(O2)peak); C(TB)). Importantly, exercise volume (300 kcal/session) was held constant for subjects in both the T(H) and the T(M) groups. V(O2)peak 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 T(H) (21%; P = 0.02) compared with the T(M) (16%; P = 0.17) and C(TB) (8%; P = 0.37) groups and were observed without changes in either body composition or V(O2)peak. Likewise in the T(H) group, we detected a significant improvement in insulin-stimulated suppression (%) of adipose tissue lipolysis at the low-insulin dose (38-55%, 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.