Table top alternate LL lowering (Core/abdominal stabilization, extending leg (alternate), legs 90/90, supine)

Lie on your back and bring your legs up to a table-top position with your hips and knees at a right angle.
Relax your upper body as you extend one leg down to the floor, whilst maintaining the table-top position with the other.
Bring this leg back up and repeat with the other leg.
Ensure you keep your core strong and back flattened to the floor throughout this exercise.