Lie flat on a floor mat. Grasp a light dumb-bell (2-3kg) in each hand and position your arms at the sides of your chest. Lift your upper back off the floor to get into a crunch position.

Keep your heels glued to the mat. Extend your right arm (as if you were throwing a punch) over your left knee and hold for one second. Try to lift your shoulder as high as you can off the mat. Return to the starting position; then, without resting, lift and extend your left arm to your right knee in the same manner. Repeat.

Added difficulty: Lift your legs and bend 90 at the knees to engage your lower abdominals.