Figure 1. Study design. Session 1) 30-15 intermittent fitness test (30-15 IFT). Gas exchanges and heart rate recorded. Session 2 and 3) A standardized warm-up based on movements and running. High-intensity interval training with constant intensity interval (HIIT-C) and high-intensity interval training with fast start strategy (HIIT-FS). Intensity was prescribed as a percentage of the individual’s speed of 30-15 intermittent fitness test (VIFT). Gas exchanges, heart rate and external load were recorded. Rate of perceived exertion was recorded after the HIIT sessions.