Weekly HIIT Time Calculator

HIIT — High-Intensity Interval Training

HIIT means trading off short bursts of near-maximal effort with brief stretches of recovery. Two protocols you'll hear about a lot are Tabata (20s work / 10s rest × 8 rounds = 4 min, Izumi Tabata 1996) and the Gibala protocol (30s all-out sprint / 4 min recovery × 4–6, Martin Gibala, McMaster University).

What makes HIIT appealing is how much it does in so little time. Studies report VO2max gains of 10–15% in 6 weeks, better insulin sensitivity, and more mitochondrial enzyme activity. One effect worth knowing is EPOC (Excess Post-exercise Oxygen Consumption), which keeps your metabolism running high for hours after the session and adds to the total calories you burn.

Applications

Aim for 1–3x/week. HIIT asks a lot of the body, and overdoing it pushes you toward overtraining, elevated cortisol, and recovery that never quite catches up. You'll see it done as sprint intervals (running, bike, rower), kettlebell complexes, burpees, or jump rope. It also fits nicely alongside Zone 2 cardio in a polarized plan, where Zone 2 builds the aerobic base and HIIT sharpens the top end.

FAQ

Can HIIT replace longer cardio? Only up to a point. It's an efficient way to raise VO2max and metabolic health, but it won't give you the mitochondrial density or aerobic durability that sustained Zone 2 work does. Pairing the two is what gets you the best results.

How intense is “high intensity”? Your work intervals should hit ≥85–95% of HRmax (RPE 8–10/10). A quick test: if you can get out more than 1–2 words mid-interval, you're not really doing HIIT. That's more likely Zone 3 or threshold work.

Is HIIT safe for beginners? It can be if you ease in. Start with longer work-to-rest ratios (say 30s/90s), pick low-impact options like the bike or rower, and keep it to 1 session a week. Spend 4–8 weeks building an aerobic base with Zone 2 first. If you have a cardiovascular condition, check with a physician before you start.