Physiological Adaptations to Sprint Interval Training with Matched Exercise Volume

Purpose This study aimed to determine how high-intensity interval training (HIIT) protocols featuring matched times but distinct sprint durations affect cardiorespiratory and metabolic responses and performance. Methods Thirty-eight recreationally active men (age 21 ± 2 yr) were assigned to one of three interval training groups: long-duration high-intensity (HIIT60s; 8 × 60 s at 85%-90% V-O 2max; 120-s recovery at 30% V-O 2max), short-duration high-intensity (HIIT10s; 48 × 10 s at 85%-90% V-O 2max; 20-s recovery at 30% V-O 2max), and control (regular physical activity without HIIT). Before and after a 4-wk training period (three sessions per week), participants performed graded exercise tests and repeated sprint tests, based on which their aerobic and anaerobic capacities were assessed. Skinfold thickness, blood, and metabolic responses were also measured before and after intervention. Results After the 4-wk training period, V-O 2max was significantly increased (P < 0.01) in HIIT60s (52 ± 9 vs 61 ± 12 mL·kg -1 ·min -1) and HIIT10s (53 ± 10 vs 61 ± 10 mL·kg -1 ·min -1), but there were no changes in the control group (50 ± 7 vs 52 ± 7 mL·kg -1 ·min -1). Skinfold thickness in the abdomen and thigh did not differ significantly among the groups, but a significantly greater decrease in 14%-25% in HIIT60s and a decrease in 20% in HIIT10s after training (P < 0.05) were found. Blood lactate, total cholesterol, triglyceride, cortisol, and insulin concentrations were not significantly different among the three groups (P > 0.05), but testosterone concentration in the HIIT10s was higher after training than before (P < 0.05). Conclusion The higher incremental aerobic performance and lower skinfold thickness in HIIT60s versus HIIT10s reflected similar adaptations, but the higher repeated sprint performance was observed only in responses to HIIT60s, which may elicit greater anaerobic adaptations.