Which of the following is NOT a sign of overtraining?

Improved muscle strength is indeed not a sign of overtraining. Overtraining syndrome occurs when there is an imbalance between training intensity and recovery, leading to physical and psychological stress. Common signs of overtraining include frequent illnesses, such as colds, as the immune system may be compromised due to excessive stress on the body. An increased resting heart rate can also be an indicator, as the body struggles to recover and adapt from the strain of intense training. Chronic fatigue is another prevalent symptom, indicating that the body is not replenishing its energy stores effectively and may be in a state of constant exhaustion.

In contrast, improved muscle strength generally suggests that training is effective and that the body is responding positively to the exercise stimulus. When an individual is not overtraining, the body typically strengthens and adapts to the stresses of workouts, resulting in increased strength and performance. Thus, an increase in muscle strength would be contrary to the signs and symptoms associated with overtraining.