Exercise balls have caused a revolution in home fitness. Unlike big, bulky machines that take up too much space, exercise ball workouts can be done in smaller amounts of space, yet yield terrific results when done consistently.

First, be sure you have the proper size and type of exercise ball. In general, people who are 4'11" to 5'4" to should get a 55 cm ball; people who are 5'5" to 5'11" should get a 65 cm ball and people who are 6' to 6' 7" should get a 75 cm ball. However, test the ball by sitting on it before you buy; your hips should be level with your knees or just slightly above them.

It's also crucial to keep good alignment with the ball. Don't tilt backward or forward while seated on the ball. Also be sure to keep the stomach muscles tightened while exercising to get the greatest benefit.Next, learn to maintain proper alignment on the device, which means don't lean forward or back while in the seated position. Be sure to tighten the abdominal muscles while exercising. Good alignment will keep you safe and get the most benefit from each exercise.

Here are a couple of exercise ball workouts to try. Most balls come with exercise instructions included.

Crunches: Position your middle back on the ball with feet flat on the floor separated about shoulder width apart. Place the hands behind the head. Raise upper body using abdominal muscles. Be sure not to pull on the neck. Repeat 8-10 times. It's also possible to do crunches while lying on the floor with the ball placed beneath the feet or the ankles. Keep the legs at a 90-degree angle. Place the hands behind the head, but don't pull on the neck. Tense abs and raise shoulders toward knees. Hold a few seconds, then release the stomach muscles and return to start. Repeat 8 to 10 times.

Hamstring Curls: Lie on a mat or floor on your back with the exercise ball placed under your heels. Keep your palms flat on the mat or floor. Raise hips slightly and bend knees to draw the ball toward buttocks, without moving hips. Repeat 8-10 times.