An acute bout of endurance exercise but not sprint interval exercise enhances insulin sensitivity

An acute bout of endurance exercise (EE) enhances insulin sensitivity, but the effects of sprint interval exercise (SIE) have not yet been described. We sought to compare insulin sensitivity at baseline and after an acute bout of EE and SIE in healthy men (n = 8) and women (n = 5) (age, 20.7 ± 0.3 years; peak oxygen consumption. (VO_2peak), 42.6 ± 1.7 mL·kg^-1·min^-1; <1.5 days·week ^-1 structured exercise; body fat, 2.1.1 ± 1.9%). Subjects underwent 3 oral glucose tolerance tests (OGTTs) the day after each of the following 3 conditions: no exercise, baseline (OGTT_B); SIE at 125% VO₂ peak (OGTT_SIE); and EE at ∼75% VO_2peak (OGTT_EE). SIE and EE sessions were randomized for each subject. Subjects consumed identical meals the day preceding each OGTT. Two insulin sensitivity indices - composite whole-body insulin sensitivity index (ISI-COMP) and ISI-hepatic insulin sensitivity (HOMA) - were calculated, using previously validated formulas (ISI-COMP = 10000√(glucose_fasting × insulin_fasting × glucose_mean OGTT × insulin_mean OGTT); ISI-HOMA= 22.5/ (insulin_fasting × glucose_fasting)). and the plasma concentrations of cytokines interleukin-6 and tumor necrosis factor-α were measured. There were no differences by sex for any condition (men vs. women, p > 0.05). Pearson's correlation coefficients between ISI-COMP and ISI-HOMA for each condition were highly correlated (p < 0.01), and followed similar patterns of response. ISI-COMP_EE was 71.4% higher than ISI-COMP_B (8.4 ± 1.4 vs. 4.9 ± 1.0; p < 0.0.1) and 40.0% higher than ISI-COMP _SIE (8.4 ± 1.4 vs. 6.0 ± 1.5; p < 0.05), but there was no difference between. ISI-COMP_B and ISI-COMP_SIE (p = 0.182). VO_{2 peak} was highly correlated with both ISI-COMP and ISI-HOMA during baseline and SIE test conditions (p < 0.02). These findings demonstrate that an acute bout of EE, but not SIE, increases insulin sensitivity relative to a noexercise control condition in healthy males and females. While these findings underscore the use of regular EE as an effective intervention strategy against insulin resistance, additional research examining repeated sessions of SIE on insulin sensitivity is warranted.