High-intensity interval training (HIIT)
Last reviewed 25 August 2026 · Evidence-graded review — see Methodology
Short bursts of hard effort separated by easy recovery: 30 seconds to 4 minutes hard, repeat. HIIT improves fitness faster per minute than steady work, and fitness is strongly tied to living longer. What is missing is direct proof that the intervals themselves cut deaths, which keeps this at Moderate.
A meta-analysis of 27 trials comparing HIIT with continuous endurance training found VO2max improved more with intervals for the same amount of total work. Higher VO2max predicts lower mortality across very large cohorts. The inference chain is solid but indirect: interval training has not been tested against hard outcomes in a long randomised trial of its own.
Doing it: Once or twice a week is plenty alongside, not instead of, easy volume. A workable session: 5 minutes warm-up, then 4 × 4 minutes hard with 3 minutes easy between, then cool down. Hard means breathing hard enough that talking is awkward.
Who it suits: Healthy adults who already have a base of regular activity. If your heart, joints or blood pressure are managed conditions, clear the top end with your doctor first.
Sources
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