Insulin resistance, an impaired ability of the tissues to respond to insulin, is a prevalent health concern in the U.S., with 8.3% of the population diagnosed with diabetes. Numerous studies have found exercise programs increase insulin sensitivity, but research on the effects of high intensity interval training on insulin sensitivity is limited. Of those studies, few have observed the length of the effect of a single bout of high intensity interval training (HIT) on insulin sensitivity to determine the minimal exercise time and frequency that stimulates improved insulin sensitivity. Purpose: This study investigated the length of the effect of a single bout of HIT on insulin sensitivity and glucose tolerance in young overweight/obese males. Methods: Ten overweight/obese men aged 20.9 ± 2.0 y participated. An oral glucose tolerance test (OGTT) was performed five d prior to the exercise trial to determine basal insulin sensitivity. Participants completed eight 30-s intervals with 4 min recovery between each (HIT). Two, three and four d post-exercise, OGTTs were performed. Results. The IG index was significantly lower 48 h post-exercise compared to baseline (10128 ± 3910 vs 4867 ± 2080, P=0.013) demonstrating improved insulin sensitivity, but was not significantly different from baseline at 72 h ( + ) or 96 h ( + ) post-exercise. Plasma glucose concentration was significantly lower at 60 min during the OGTT 72 h (7.1 ± 0.7 vs 8.2 ± 0.6, P =0.033) and 96 h (6.9 ± 0.7 vs 8.2 ± 0.6, P =0.023) post-exercise, but was not significantly different from baseline at 48 h post-exercise. Conclusion. An acute bout of 8 x 30 s high intensity interval exercise results in significantly improved plasma glucose concentrations at 60 min during an OGTT at 72 and 96 h post-exercise. A single bout of HIT improves insulin sensitivity for 48 h in sedentary, overweight/obese young men.