Slide show: Core-strength exercises with a fitness ball

When you're comfortable doing the bridge with the fitness ball, add a heel dig for more core strength:

1. Lie on your back with your legs resting on top of the ball. Raise your hips and buttocks off the floor into a bridge (A).
2. Tighten your abdominal muscles.
3. Keep your hips off the floor while you pull the ball closer to your buttocks with your feet (B). Dig your heels into the ball for traction and to engage the muscles along the back of your thighs (hamstrings). Hold for three deep breaths.
4. Return to the start position and repeat.