Start by laying down flat on your back, with your knees bent and feet flat on the floor.
Use your core to lift your torso and sit all the way up, so that your shoulders are stacked directly atop your hips. Finish the movement by reaching your hands up to the ceiling for a full extension of your core.
Slowly lower back down to the starting position and repeat four rounds of 10-15 repetitions, resting just long enough to recover in between rounds.
If this variation is too difficult, place a weighted object on top of your toes for additional leverage.