A combination of HIIT and low- to moderate-intensity exercise training — which elite athletes use — is likely the best way to improve aerobic exercise performance. Research shows that combining HIIT with moderate-intensity training is more effective for improving aerobic capacity than moderate-intensity training alone.[1] However, when workouts are matched for energy expenditure, HIIT may improve VO2max by an additional 1.2–3.3 mL/kg/min versus moderate-intensity training,[2][3] despite requiring an approximately 2- to 3-fold lower time commitment.[4]
Lower-volume HIIT — also known as sprint-interval training (SIT) — consisting of maximal effort 30-second sprints is shown to improve running economy and 10-kilometer time trial performance in runners.[5] However, longer intervals (2–4 minutes) may be more effective for improving VO2max compared to shorter intervals (10–30 seconds). Additionally, for HIIT to be most effective at improving VO2max, the ideal workout duration should be greater than 15 minutes.[3]