Boo! is a Halloween core workout that behaves exactly like its namesake - long quiet stretches, then something jumps out at you: one jump squat, a 10-count plank hold, one jump squat, a 10-count side plank, one jump squat, a side plank on the other side, and one final jump squat. Four single jump squats, haunting the gaps between three holds.

A single jump squat is the jump scare of exercise programming. Ten in a row you can pace and prepare for; one, arriving out of stillness, demands everything at once - full depth, maximal drive, controlled landing - with no rhythm to hide inside. Placing each one immediately after an isometric hold sharpens the scare: your body settles into the quiet, steady-state effort of a plank, your nervous system dials into stillness, and then the workout leaps out from behind the door and asks for peak power with zero warm-up into it. That transition - static to explosive in a single beat - is a genuinely valuable athletic quality, and almost nothing trains it. The two side planks make sure both sets of obliques take a turn holding the haunted house together.

Make each single jump squat a complete performance: sink to full depth, jump for real height, land soft and quiet - a ghost, not a poltergeist. In the plank, push the floor away and hold one line from head to heels. In side planks, stack your shoulder over your wrist, lift your hips high and reach the top arm to the ceiling. Between stations, move without dawdling; the scare only works if you don't see it coming.

The scariest number in fitness turns out to be one. Boo.

Make it Harder: Make every jump scare a double - two jump squats at each station.

Make it Easier: Swap jump squats for regular squats and take the side planks from your knees.