The breakdown of skeletal muscle cells, rhabdomyolysis, is often caused by physical exercise. The exact mechanism of muscle injury is poorly understood. When injured, muscle cells release enzymes into the bloodstream, which can be detected on laboratory examination. In most cases, the amount of breakdown is minimal and patients suffer no ill effects from this condition. In severe cases, however, potentially life-threatening complications such as acute renal failure may develop. Risk factors, methods of diagnosis, treatment, and reconditioning are summarized.