The condition, which is the second most commonly diagnosed musculoskeletal disorder after osteoarthritis, is described by Richard B. Gremillion, M.D. ``as a noninflammatory, diffuse pain syndrome of unknown cause."

In his article for The Physician and Sportsmedicine publication in April, Gremillion identifies the most common symptoms as debilitating fatigue and severe muscle pain, which typically clusters around the neck and lower back. But other symptoms include swelling in soft tissue, stiffness, tender points and muscle spasms.

Often confused with rheumatoid arthritis and chronic fatigue syndrome, the exact cause of FM remains unknown. What is known, however, is that FM:

It strikes women more often than men. FM usually develops between puberty and menopause. It can be treated, in part, by exercise. In addition to conditioning the affected muscles, exercise often relieves depression and improves the quality of sleep. However, experts emphasize caution when designing an exercise program for FM patients. Because pain is an almost constant companion, workouts should be low- to non-impact (cycling, swimming, walking). Studies indicate that aerobic exercise is best.

If you enjoy dancing, the following exercise is a great way to increase your heart rate and gently challenge your muscles. Warm up for at least five minutes with movements that use the large muscle groups of your body.

Stand with your feet slightly wider than shoulder width apart and your knees slightly bent. Leading with your hips, shift your weight from right to left in time with the music. Keep your weight on the balls of your feet so that your feet can easily pivot as you do this.

To add more intensity to the movement, you can add arm movements of your choice, alternating them overhead as shown or keeping them low if you prefer.

As with any exercise, make sure you are standing tall with your abdominal muscles in and your shoulders relaxed. Alternate this exercise with others for at least 10 minutes of vigorous dancing. As you become more fit, you can gradually build up to 30 minutes of continuous dancing.

Always end your workout with at least five minutes of slow, cool-down movements and stretching to allow the heart rate to gradually return to a normal level.

Judi Sheppard Missett is CEO of Jazzercise Inc., an international aerobic dance instruction company.