Rolling Hamstring Curl
Works: thighs, hips, butt, calves (Bonus: core)
A. Lie on your back with legs straight, heels resting on top of ball and arms on the floor.
B. Tighten abs and lift hips off the floor until your body forms a diagonal line from shoulders to heels. With back straight, hold hips high and bend legs so ball rolls toward you; the soles of your shoes touch the ball.
C. Straighten your legs but keep hips raised. Do eight to 12 reps.