A

SETUP Strengthens buttocks and upper fibers of the hamstrings; works ab and back muscles as stabilizers - Kneel on all fours with elbows in line with shoulders and forearms on floor, hands clasped and knees in line with hips. Then place a stability ball behind right knee and hold it in place by pressing right heel against the ball. - Contract abs so body forms straight line from head to hips.

B

ACTION - Maintaining torso position, contract buttocks muscles as you lift right knee up to hip height, keeping hips square. - Slowly lower knee to floor, then repeat for 15-20 reps. Switch legs and repeat for 15-20 more reps. Trainer's Tip: Move your leg upward in an arc so sole of foot faces ceiling at top of movement. If you have trouble controlling the ball, deflate it slightly or switch to a smaller ball.