5-Minute REHIT is the gentlest doorway into REHIT - reduced-exertion high-intensity training - the protocol built on the finding that two brief, honest sprints inside a few minutes of easy movement can move the needle on cardiovascular fitness more than long sessions of moderate effort. This version needs no floor, no equipment and no burpee tolerance: march steps or half step jacks carry the easy minutes, and high knees carry the sprints. Five minutes, start to finish, including the parts that feel like a stroll.

This one works differently from the usual Darebee circuit: it's one continuous timed sequence - 90 seconds easy, 20 seconds of all-out high knees, 90 seconds easy, 20 more all-out seconds, then 80 easy seconds to land the plane. The architecture matters more than the exercises. The two 20-second windows are where the adaptation is bought: a genuinely maximal burst drains the working muscles' ready fuel fast, and that sudden demand is the signal the heart, lungs and metabolism reorganize themselves around. The easy segments in between are load-bearing too - they keep you warm and moving so the second sprint can be as honest as the first. Where its sibling workout spends those windows on burpees, this one keeps everything standing, which makes it the version you can do in a hallway, a hotel room or a mood.

Treat the easy segments as genuinely conversational - relaxed march or soft half jacks, shoulders loose. When the 20 seconds arrive, sprint in place like the floor is timed: knees driving to hip height, arms pumping hard, the fastest turnover you own. Don't ration effort across the two windows; each one deserves everything, and each one is over before regret forms.

Five minutes, twice all-out, done before the kettle boils. Efficiency this good should probably cost more.

Make it Harder: Upgrade the easy segments to full step jacks while keeping both sprint windows maximal.

Make it Easier: March all the easy segments and run the high knee windows at a brisk jog instead of a sprint.