Previous research demonstrates that moderate-intensity aerobic exercise improves insulin effectiveness. Whether higher exercise intensities improve insulin action more so is unclear. The purpose of this study was to evaluate the effect of various levels of aerobic intensity on insulin action in young adult men and women. Forty-five healthy subjects (22.2 ± 3.9 years; 169 ± 9 cm; 74.5 ± 17.8 kg) were matched for age, gender, and VO2max and randomly assigned to moderate-intensity (50% heart rate reserve [HRR]), vigorous-intensity (75% HRR), maximal-intensity intervals (95/50% HRR) or a non-exercising control group. Subjects completed a 6-week training protocol on a stationary bicycle ergometer. Weekly duration and frequency of training varied to ensure equivalent energy expenditure across groups. The homeostasis model assessment (HOMA) and quantitative insulin sensitivity check index (QUICKI) were used to assess insulin effectiveness. Significant increases occurred after training in VO2max in the vigorous-intensity(15.4%) and maximal-intensity(14.2%) groups (p < 0.01) but not the moderate-intensity or control group. There were no significant changes in insulin effectiveness in any exercise group. Training intensity did not significantly affect insulin effectiveness in a young adult population as assessed by HOMA or QUICKI; it did, however, significantly affect VO2max.