What is a common symptom of overreaching?

Chronic muscle tenderness is indeed a common symptom of overreaching. Overreaching occurs when an athlete increases their training intensity or volume to the point where they surpass their body's ability to recover. This can lead to muscle soreness and tenderness due to repeated microtrauma to the muscle fibers without adequate recovery time. This tenderness can be indicative of the body struggling to repair itself, reflecting a state of physical stress that can leave the athlete vulnerable to further fatigue, injury, or even progression into overtraining if not addressed. The other choices suggest positive aspects such as enhanced concentration, improved muscle performance, and increased energy levels, which are not typically associated with the stress and fatigue that accompany overreaching. These conditions reflect states of optimal performance, which are not characteristic of an athlete who is overreached and in need of recovery.