Starting Position: Lie flat on your back on the floor / mat in a bent-knee position with feet placed firmly on the floor and arms at your sides. Stiffen (“brace”) your abdominal muscles to stabilize your spine, depress and retract your scapulae (pull shoulders back and down) and attempt to hold these positions throughout the exercise. Slowly lift both feet off the floor, extending your knees until your thighs are aligned vertically with the floor, and allowing your toes to point away from your body (DO NOT move your thighs beyond this point as it shifts your body weight from your butt into your low back, which increases the stress to your low back). Position your hands on your thighs (front or side) without lifting your shoulder blades off the floor / mat.
Gently exhale, contract your abdominals to flex (curl) your trunk, lifting your scapulae (shoulder blades) off the floor, slowly sliding your hands down your thighs towards your ankles. Maintain your head position aligned with your thoracic (upper) spine and avoid flexing your head too far forward. This movement will press your low back into the floor / mat.
Continue curling upward until your scapulae (shoulder blades) lift completely off the floor and hold this up-position briefly for 5 - 10 seconds then slowly return downwards to your starting position and repeat the movement. Complete a set of quality reps until your experience fatigue or until your technique (form) becomes compromised.
To maximize the benefits of this exercise and reduce the potential for injury, it is important to control your movement speed, keep your thighs aligned vertically and roll your trunk upwards and downwards during the exercise.