A Sit on the edge of a sturdy chair or box, leaning back slightly. Pull abs in tight, and bend knees about 90-degrees. Point toes lightly on the floor, and bend elbows and hands in front of shoulders.
B Quickly lift knees up and lightly tap thighs with hands, sitting upright as you draw legs in. Immediately return to start and repeat as quickly as possible for 45 seconds. Tip: Think 'up' during this movement—try to accent the lift, rather than the lowering, of the legs to work your abs more and help keep your heart rate high.