HIIT

How hiit burns calories

HIIT alternates brief maximal-effort intervals with short recovery periods, which spikes your heart rate repeatedly rather than holding it at one steady level. That repeated spiking is what drives the high MET value, and it also triggers excess post-exercise oxygen consumption — your metabolism stays elevated for a while after you've stopped.

At 8.0 MET, a HIIT session burns calories at the same rate as tennis or a moderate-pace cycling session, but compressed into a shorter total time.

What changes the real number

• Work-to-rest ratio: a 1:1 ratio sustains a higher average effort than a 1:3 ratio
• Movement selection: full-body moves like burpees or kettlebell swings cost more per interval than isolated moves
• Effort ceiling: HIIT only works at the intensity implied by the name — intervals done at moderate effort are no longer HIIT
• Session length: most of the metabolic benefit comes in the first 15-20 minutes of genuinely maximal effort

Technique notes

• Treat the work interval as genuinely maximal — if you could hold a conversation through it, the intensity isn't high enough to count as HIIT
• Use the rest interval fully; cutting recovery short just degrades the next work interval
• Warm up properly before the first all-out interval — HIIT's injury risk is concentrated in the first few minutes of cold, explosive effort
• Limit true HIIT sessions to 2-3 times a week; the intensity that makes it effective also makes it taxing to recover from

How it compares