Six million people a year see a doctor for back pain and approximately 16 percent of the population has endured pain lasting two weeks or more. For those with aching backs, working out and being active can either hinder you-inappropriate exercise is the root cause of most recurrent low back problems-or help you, depending upon whether you know how to strengthen the back and shore up the surrounding muscles. In general, a regular combination of aerobic, strength and flexibility training can bolster weak spots and help keep you out of the pain zone.

Strength Exercises: Most individuals with a history of low back pain have poor muscle endurance in their low back muscles. The area may be strong but the muscles fatigue rapidly with repeated contractions. The same thing goes for the abdominal muscles, although to a lesser extent. You can improve muscle endurance in your back and abs by gradually increasing the number of repetitions and sets that you do. Just be sure to avoid large movements (you don't need to use a wide range of motion to affect the muscle) and keep your back as straight as possible; many low back problems are caused by repeatedly flexing the trunk muscles (e.g., bending forward), but severely hyperextending the back is equally dangerous. (Any combination of rotation and flexion, as in a golf swing, is also very detrimental.)

Flexibility Exercises: The tighter your hamstrings are, the likelier you are to suffer back pain because tightness in this area transfers strain from the hips to the low back. Unfortunately, many people don't know how to stretch their hamstrings correctly. When doing hamstring stretches, always try to maintain a relatively straight back. Putting a foot up on a chair and bending your head toward your knee is not an appropriate stretch for someone with low back pain. Instead, lie on your back in a doorway, raise one leg and place it against the door frame (keep the leg as straight as possible). Keep the other leg straight on the floor. You can increase the stretch by moving your hips closer to the frame. If you can comfortably hold a stretch with your leg at a 90-degree angle to your torso, you have good hamstring flexibility.

Don't just focus on your hamstrings, though. Illiotibial band (the muscle that runs up the outer thigh) flexibility is also important for people with low back problems. To stretch this area, lie flat on your back, bend your right knee approximately 90 degrees and let it fall across your body to the left side. Hold for 10-30 seconds and repeat with the other leg. If you're really tight, you'll probably feel this most along the outside of your butt.

Aerobic Exercise: One of the problems that anyone with persistent low back pain encounters is getting out of shape. If your symptoms last for several weeks, you may become sedentary and lose aerobic fitness. Then, when (or if) the pain finally goes away, you can't work out nearly as hard or as long as you used to, and if you try to do more than you're ready for, your back starts to hurt again. The key to getting in shape under these circumstances is to find some kind of workout that doesn't stress the back. Try the Nordic Trac or StairMaster; both place minimal pressure on the back.

While these guidelines may be helpful, if you have low back problems you should always get a complete diagnosis and treatment suggestions from a sports medicine physician or orthopaedic surgeon before you start or return to an exercise program.