HIIT
Short, hard efforts that pay off fast.
Short bursts, brief rests
HIIT stands for high intensity interval training: short bursts of near-maximal effort followed by brief recovery periods, repeated for a set number of rounds. A simple example is 30 seconds of hard effort (sprinting, cycling, kettlebell swings) followed by 30 to 90 seconds of rest, repeated for 15 to 20 minutes total.
Efficiency, with a tradeoff
HIIT delivers a strong cardiovascular and metabolic stimulus in less time than steady state cardio, and it keeps your body burning extra calories for a while after the session ends. The tradeoff is fatigue: because the effort is maximal, HIIT is more taxing on the nervous system and takes longer to recover from than LISS.
15 to 20 minutes
A complete session, warmup aside. Intensity is the point, not duration.
2 to 3 times a week
Plenty for most people, especially alongside strength training.
Respect the recovery
More than that tends to cut into recovery without adding proportional benefit.
The gold standard
Norwegian 4x4
Four minutes hard, three minutes easy, four times through. Few protocols have more research behind them, and none are a more reliable way to raise VO2 max. HIIT has plenty of other formats (Tabata, EMOM, and more below), but this is the one the science keeps coming back to.
Inside the 4x4 →