Nicole Krupa: Core exercises strengthen your core muscles, including the muscles in your abdomen and back. You can do many core exercises with a fitness ball. Let's try the abdominal ball raise.

Lie on your back and rest your legs on top of the ball. Your legs should be about hip-width apart.

To begin the exercise, tighten your abdominal muscles and squeeze your legs together. The ball will create resistance for your inner thigh muscles. To protect your low back, focus on pulling your bellybutton in toward your spine and keeping your abdominal muscles contracted.

Raise the ball off of the floor. Hold for three deep breaths. Then return to the starting position.

If you're just starting out, repeat the exercise five times. To make the exercise more challenging, raise the ball off of the floor and then let your legs slowly fall to one side. Stop before you reach the floor. Hold for three deep breaths, keeping your shoulders on the floor. Return to the starting position and repeat on the other side.

Remember to breathe freely and deeply throughout the exercise, and keep your abdominal muscles nice and tight. As you get stronger, gradually increase to 10 to 15 repetitions.

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