HOW: Start by laying flat on your back. Perform the exercise by flattening your low back into the ground, stiffening your legs to keep them straight, then reach forward and towards the ceiling with your arms straight as you perform a sit up while keeping your legs straight and flat on the ground. Lower down with good form and repeat.
FEEL: You should feel your abs, legs, and core working with this exercise.
COMPENSATION: Do not let your knees bend or your heels lift off the ground as you lift your body up and down. Do not let your low back excessively arch as you perform the sit up. Avoid using excessive momentum to perform the sit up.