This exercise works your spinal stabilising muscles, which helps you pedal smoothly, not slump down and helps prevents rocking hips by working your gluteal and oblique abdominal muscles.
Start by laying on your back with your knees bent up and your feet a crank’s width apart. Make sure your shoulders and neck are relaxed.
Lift your back from the floor starting at your tailbone and working up your back, concentrate on using your gluts and not arching up with your back. If you can maintain this position without gripping on with your back muscles then try and lift one leg then the other whilst keeping your back still and pelvis level. Lower down to the floor and repeat.
Make sure you keep breathing, your ribs, shoulders and neck are relaxed and your hips are level.