Overtraining syndrome affects athletes by causing a decline in performance, increased fatigue, mood disturbances, and elevated injury risk. This condition arises when training intensity and volume exceed the body's ability to recover. Symptoms may include persistent soreness, insomnia, and decreased motivation to train. Overtraining can also disrupt hormonal balance, affecting cortisol and testosterone levels, leading to physical and mental health issues. It is essential for athletes to incorporate adequate rest and recovery into their training regimens to prevent overtraining and maintain optimal performance and well-being.