Just like motor oil keeps your car running smoothly, there's an important fluid that lubricates and nourishes your joints. This substance is called synovial (syn ö vi àl) fluid, and joints that contain it — like your shoulders and hips — are called synovial joints.

As you move, sacks of this fluid cushion your knees and elbows against friction, and these sacks are known as bursae (bûr`s∂). When you hear people talk about tennis elbow — outer elbow pain often caused by repetitive motion — they actually have inflamed bursae, which physicians refer to as bursitis.

Joint pain can interfere with your physical activity and daily life. The flip side, however, is that as your fitness level increases, joint pain may decrease. Here are some things you can do to encourage both of these desired results:

• Warm up before any activity. Try this for your knees: Sit in a chair, and slowly raise your left foot until your leg is straight. Hold for a second, and slowly lower it. Repeat this motion 10 to 15 times with each leg.
• To warm up your hips and get a great back massage in the process, lie on your back with your knees bent in toward your chest. Slowly move your knees in gentle circles, keeping the small of your back on the floor. Repeat the motion 10 times, and then switch directions.
• If you use weights, choose lighter weights and do more repetitions. Eventually, work up to heavier weights.
• Be sure to use correct form as you exercise. For example, never do any activity that causes you to bend your legs until your knees stick out beyond your toes. This position puts too much pressure on your knees.

(Note: Be sure to check with your physician before starting any new fitness regimen.)