What is a common physiological symptom of overtraining?

Lethargy is a common physiological symptom of overtraining because it reflects the body's struggle to cope with the excessive physical and mental demands placed on it. When an athlete trains beyond their capacity to recover, it leads to a decrease in performance and an overall feeling of fatigue. This state is often characterized by a long-term reduction in energy levels, making it difficult for the individual to perform at their usual intensity, which can also lead to decreased motivation and productivity in training sessions.

In contrast, anxiety can be a psychological symptom rather than strictly physiological, while increased appetite might occur in some instances due to higher calorie expenditure during intense training, not as a direct symptom of overtraining. Enhanced recovery typically implies optimal performance and training conditions, which contradicts the state of overtraining where recovery is impaired. Therefore, lethargy serves as a key indicator of the body's inability to recover adequately, marking it as a principal symptom associated with overtraining.