Table top alternate LL lowering in flexion (Core/abdominal stabilization, lowering/lifting bent leg, supine legs 90/90)

Lie on your back with your legs bent and your feet flat on the floor.
Place your hands on your abdomen and tighten your abdominal muscles.
Raise one leg, and then the other leg, up to the table-top position, with your hips and knees at 90 degrees.
Maintaining a strong stable position with your back, lower one heel down towards the floor, then return to the table-top position.
Repeat with the other leg.
Continue this movement, ensuring you do not allow your lower back to arch.