The formula couldn’t be much simpler:
Go all in for 60 seconds: running, cycling, rowing, whatever gets your pulse racing.
Slow it way down for 120 seconds. Catch your breath, bring your heart rate down.
Repeat for several rounds.
That’s it. The “fast” piece should feel tough, not comfortable, like you’re working at a pace you couldn’t possibly keep up for long. Recovery is the time to shake out your legs and let your body recover just enough to go again.
Military training isn’t cookie-cutter, though. The Army uses all sorts of intervals, like 30 seconds of work, 60 seconds of rest, and so on, depending on what a soldier needs. The big idea is always the same: expose your body to hard effort, then let it adapt.