Hollow rocks

1. 1Lie on your back on a mat with your arms overhead and your legs straight together, toes pointed.
2. 2Press your lower back flat into the floor, then lift your shoulders, arms and legs a hand's width or so off the ground so only your lower back and hips stay in contact.
3. 3Keep that banana shape rigid and rock back and forth from your upper back to your hips, driving the motion from your shoulders rather than by pumping your legs.
4. 4Breathe in short, shallow breaths through the set and keep your ribs pulled down toward your hips the whole time.
5. 5To finish, stop the rocking first, then lower your arms and legs under control rather than dropping them.

• The lower back arches off the floor and the rock turns into a flop.

  →Fix: Tilt your pelvis so your ribs close toward your hips, and raise your legs higher until the back stays pressed down.

• The body bends in the middle, so arms and legs swing at different times.

  →Fix: Think of yourself as one stiff plank and squeeze your legs, glutes and abs together before the first rock.

• Rocking so fast that momentum does the work and the shape is lost.

  →Fix: Slow the rhythm down and make each rock small and controlled, holding the hollow shape at both ends.

None of the fixed workouts uses it. Pick a workout for your kit, or start today's session on /gym.