The Interval Pattern, Rather than High Intensity, Accounts for the Superior Effects of High-Intensity Interval Exercise (HIIE) on Glucose Tolerance

PURPOSE: Some data suggest that high-intensity interval exercise improves glycemic control more than continuous exercise. We aimed to identify the factor(s) that enhance insulin sensitivity during an oral glucose tolerance test (OGTT) after exercise. METHODS: Ten healthy, physically active individuals (including three females) completed three work-matched 50-minute exercise trials that differed in workload distribution. Using a randomized crossover design, participants completed: a) a moderate-intensity continuous exercise trial (MICE), b) a high-intensity interval exercise trial (HIIE), c) a high-intensity continuous exercise trial (HICE), and d) a no-exercise control trial (CONT). After exercise, insulin sensitivity (IS MATSUDA) was measured during the OGTT. Plasma glucose kinetics and oxidation rates were measured by infusion of isotopically labeled [U- 13C] glucose. Glycogen oxidation was calculated as the difference between total carbohydrate oxidation (assessed by indirect calorimetry) and plasma glucose oxidation. RESULTS: Total carbohydrate oxidation, plasma glucose oxidation, calculated glycogen oxidation, and plasma lactate accumulation during exercise were similar between HIIE and HICE, and both were higher than during MICE (p<0.05). Only HIIE decreased the postprandial insulin area under the curve, which increased IS MATSUDA index above CONT, MICE and HICE (15.5±4.3 vs.12.7±4.4; 12.5±6.1 and 11.8±6.0; p = 0.048, 0.030, 0.005, respectively). CONCLUSIONS: In summary, improvements in glycemic control following HIIE seem to be more related to its cyclic pattern than to glycogen use during the high-intensity segments. Our data suggest that exercise programs aimed at restoring glycemic control should emphasize workload cycling before engaging the high-intensity component.