HIIT
Redirected from "High-intensity interval training"
Also known as: High-intensity interval training
HIIT, short for high-intensity interval training, is cardio built from repeated relatively hard work intervals separated by easier active recovery or rest. The recovery makes it possible to accumulate more high-intensity work than could be sustained continuously. Running, cycling, rowing, swimming, and bodyweight movements can all be used, so the acronym describes the work–recovery structure rather than one exercise.
HIIT is not the same as HIT. HIT is a resistance-training approach based on a small amount of very hard lifting, commonly near or at muscular failure. HIIT is also distinct from continuous LISS cardio and from the usually steadier aerobic work called Zone 2. A circuit counts as HIIT only when its planned work bouts are genuinely high intensity and are separated by recovery; moving quickly between stations does not establish the label by itself.
There is no single official HIIT interval. A session might use four-minute efforts, one-minute efforts, or much shorter repetitions, with complete rest or light movement between them. The work should be hard relative to the person's current capacity, but it does not always have to be an all-out sprint. Sprint interval training is the more extreme subtype built around maximal or supramaximal efforts. Work duration, recovery, number of repetitions, and exercise mode all change the stimulus and the amount of fatigue.
HIIT is effective for improving aerobic fitness. A 2024 umbrella review covering 24 systematic reviews found greater average improvements in cardiorespiratory fitness than non-exercise control and moderate-intensity continuous training. The included protocols and populations varied, and many underlying reviews had methodological limitations, so this does not make one HIIT formula universally best.
Because the hard intervals are demanding, quality matters more than turning every session into a maximal test. Use an appropriate warm-up, choose a movement you can control when tired, and stop adding intervals when pace or technique deteriorates substantially. Frequent HIIT can compete with lower-body lifting through fatigue, even if each session is short. Easier cardio remains useful when it better fits your goals, recovery, or preference.