Lie on the floor or a mat on your back, with knees bent and hands behind head. Lift legs and bend knees to 90 degrees. Keep a space between your chin and chest (looking diagonal towards the ceiling). Exhale as you draw your belly inward which will cause your hips to slightly rise off of the floor. Inhale and with control, lower your spine and hops back o the start position.
Don’t use your momentum to swing your legs up. Try to keep the motion controlled by your abs.
Please modify by bending your knees. Go at your own pace and feel free to break the reps up throughout the day.