Athletes often complain about the physical and mental effects of over-training. Over-training occurs when the amount or intensity of exercise exceeds the body’s ability to recover from the stress placed upon it. Although athletes need to push their physical limits in order to improve, repeated strenuous exercise without sufficient recovery can eventually reduce rather than enhance their performance. Over-training can occur in three main ways: failing to allow enough rest between training sessions, repeatedly training the same part of the body, and increasing the intensity or volume of exercise too quickly. A lack of rest prevents damaged muscles and tissues from repairing themselves properly. Similarly, working the same body part too frequently places repeated stress on muscles, joints and tendons, increasing the risk of overuse injuries. Athletes who suddenly increase their workload may also demand more from their bodies than they are physically prepared to tolerate.