Initial action: prone on the bent leg, with the knee just above the end of the prone board. Adjust the resistance roller pad so that the back of the ankle is just below the roller pad. Grab the handle and take a deep breath.
Action process: keep the trunk straight, contract the biceps femoris to move the rolling pad to the buttocks, and when the action reaches the midpoint, start exhaling. At the top of the action, squeeze your biceps femoris hard, and then slowly reverse back to the initial position.