The back is a complex joint that's supported by large muscle groups. It's important to keep back muscles strong and flexible to avoid injury. There are certain exercises you can do to strengthen your back, depending on your fitness level. Walking and running help strengthen lower back muscles and stair climbers work these muscles as well. Swimming is one of the best exercises to strengthen the entire body in a weightless environment. It's an exercise almost everyone can do without injuring joints. You can also specifically target the muscles of the back in several safe exercises. Lying on your stomach and lifting your legs off of the floor one at a time works the muscles in your upper and lower back. You can also lie on your stomach and raise your chest off of the floor to target upper back muscles. There are other exercises you can perform with and without weights, but it's best to consult your chiropractor for the proper positioning and amount of weight you should use. If you have a back injury, however, you should consult your chiropractor before doing any exercise.