Jackknife sit-ups

These combine a leg raise and a sit up to work both upper and lower abs simultaneously.

Step 1: Lie down on the floor with your hands stretched out behind you.

Step 2: Exhale as you raise your feet off the floor while keeping your knees straight till they reach a 45 degree angle, at the same time raise your torso off the floor with your hands reaching for your toes till the point where your legstouch your chest and pause for a second.

Step 3: Lower yourself down in a controlled movement while inhaling.

Step 4: Repeat as many times as possible.

Beginners: Skip the pause at the top of the rep, but do lower yourself down slowly.

Experienced readers: place a small medicine ball between your legs to up the difficulty.