HIIT

Move · High-Intensity · Movement, Typed Supps

Short, hard efforts that keep burning calories after you stop.

Stage by stage

Warm-up (Primes fast-twitch fibres): A brief warm-up raises heart rate and primes fast-twitch muscle fibres for near-maximal effort.
During (Stored energy systems used): Very high-intensity intervals rely heavily on stored muscle energy rather than the slower aerobic system used in steady cardio.
Immediately after (Elevated oxygen use (EPOC)): Oxygen consumption stays elevated for a period afterward as the body restores energy stores — known as EPOC.
Days later (Dual-system adaptation): Muscles adapt to tolerate high-intensity intermittent effort, and cardiovascular fitness improves through a different pathway than steady-state cardio alone.

Muscles trained

Primary: heart, lungs
Secondary: quads, glutes

Intensity

8 METs (Circuit training, including kettlebells, some aerobic movement with minimal rest, general, vigorous intensity).

Time to effect

Weeks: Improvements in both aerobic and anaerobic capacity often appear.

Related supplements

Common myth

“EPOC (“afterburn”) burns as many calories as the workout itself.” In reality: The extra calories burned during EPOC are real but modest — typically a small fraction of the workout’s own calorie burn, not a doubling effect.