Lower back flat on the floor, lower the opposite arm and leg slowly, breathe out as you reach.

How to do it

Lie on your back with the arms pointing to the ceiling and the knees bent at 90 degrees over the hips.
Press the lower back flat into the floor.
Slowly lower one arm overhead and the opposite leg towards the floor.
Stop before the lower back lifts, return, and switch sides.

Common mistakes

Breathe out fully as you reach and in as you return. Move slowly, about 2-3 seconds each way.

Harder: Hold a light dumbbell, or straighten the leg further.

Easier: Move only the legs, or only the arms.

Beginners: 2-3 sets, stopping each 2-3 reps short of failure.

Building muscle: 3-4 sets of 8-20 reps, stopping 0-2 reps short of failure. Past 20, move to the harder version.

One of the gentlest core exercises; a good start after back pain once a doctor or physiotherapist agrees.

Full gym: Cable crunch, Crunch, Hanging leg raise, Ab wheel rollout, Bird dog

Dumbbells and a bench: Crunch, Ab wheel rollout, Bird dog

Bodyweight only: Crunch, Bird dog