Supine toe tap

This is a basic exercise. It engages your core muscles while working your legs and will work your hips and spine.

Toe taps also put minimal stress on your spine. If you have back pain, toe taps can be an ideal alternative to crunches.

Start on your back. Lift your legs, bend your knees to 90 degrees. Place your hands at your sides, palms down.
Tighten your core. Lower your right leg and gently tap the floor, keeping your left leg still and your back flat.
Raise your right leg to return to the starting position.
Repeat with your left leg.

Start with 3-4 sets of 8 to 12 repetitions.