Although it takes a tremendous amount of force to destroy the back, it's easy to disrupt it. Back problems are the second most common reason for a person to see a doctor (after sore throats) and the second most common reason for absences from work (after upper respiratory infections).

To prevent back trouble during sports or other exercise, it's important to develop a conditioning program that gradually strengthens the back muscles as well as the abdominal muscles. If stomach muscles become flabby, the opposing back muscles tighten up; strengthening abdominal muscles stretches out the back muscles.

Experts suggest several back exercises, including:

* Situps. Lie flat on your back with knees bent and toes tucked under a couch. (Never do situps with legs straight -- it can strain your back.) Put your hands either at your sides or clasped behind your head. Rest your chin on your chest and curl up until your upper body is at about a 45-degree angle, but don't touch the knees. Ease down and repeat.

* Knee Touch. Standing, bend forward and touch your left knee with your right hand. Then stand up, and repeat to the right. Begin with as many as you can do comfortably, and work up to 50 to 100 repetitons. When 100 repetitions becomes easy, try it holding light weights.

* Ground Reach. Stand up and bend over slowly, reaching for the ground. Stay relaxed, with knees bent, grab your ankles and pull down gently. The same exercise can be done while sitting in a chair.

* Trunk Twist. Lie flat on the floor on your back with knees bent. Push the knees to the right, toward the floor, while keeping the shoulders flat on the floor, and then bring the knees back up. Repeat to the left side.