Hydra is a cardio and boxing workout named for the monster that made decapitation a losing strategy: cut off one head, and two more grow back. Here the heads are punches. Three separate blocks of 10 punches run through the set, and every time you finish one, the workout grows new striking work in its place - lunge punches, squat punches - each variety demanding the same hands with a fresh pair of legs attached. You don't beat this one by finishing a block. There's always another head.

The circuit runs without rest between exercises, and the mythology is in the structure. The 10-punch blocks are the recurring heads, and between them the workout keeps mutating the base movement: 4 squats interrupt the first pair, then 4 lunge punches - striking from the bottom of a lunge - appear twice around the third punch block, and 4 squat punches close the set by fusing legs and hands into one compound demand. Notice what never changes: the hands never stop working for long, but the platform under them keeps getting harder. Punching from a stable stance, then from a lunge, then from a squat teaches the body to deliver force from progressively compromised positions - which is the actual skill hiding inside the monster.

Punch with full extension and snap every hand back to guard, whatever your legs are doing at the time. Keep squats at parallel depth with chest up. In lunge punches, drop into a genuine lunge - rear knee toward the floor - and strike from the bottom rather than on the way up. During squat punches, hold your depth honestly while the hands work; the legs shaking is the exercise functioning as designed.

Heracles needed fire and a nephew to beat his hydra. You just need to keep punching - the heads stop regrowing when the set ends.

Make it Harder: Double every 4-count block - 8 squats, 8 lunge punches, 8 squat punches.

Make it Easier: Shallow the lunges and squats to half depth and keep the punch blocks at an easy rhythm.