The best part? You don’t need any equipment at all. Here’s how to do it:

• Start in a hollow body position: Lie on your back. Press your lower back into the ground. Lift your shoulder blades off the ground one inch, and your legs off the ground — all without letting your lower back lose contact with the ground. Tighten your abs to drive your lower back into the ground.

• Do a sprinter sit-up, contracting your abs then bringing right elbow to left knee; your right leg stays straight. Do 1 rep.

• After that one rep, keep your right elbow connected to your left knee; you’re now in corkscrew hollow rock position. Do one hollow rock, then return to hollow body position.

• Do 2 sprinter sit-ups; after the second one, stay in corkscrew hollow rock position and do 2 hollow rocks. Continue this pattern, laddering up to 5 sprinter sit-ups and 5 corkscrew hollow rocks.

• Rest 30 to 45 seconds. Do 3 sets per side.