What physical symptom might result from staleness due to extensive training?

The symptom of loss of appetite is typically associated with staleness, which can occur after extensive training. Staleness, or overtraining syndrome, is characterized by a decline in performance and overall well-being. This condition can manifest through various physical and psychological symptoms, one of which is a decrease in appetite.

When an athlete trains excessively without adequate rest and recovery, it can lead to hormonal imbalances and increased stress levels, contributing to a diminished interest in food. The body might prioritize energy conservation and recovery processes over the digestive system's functions.

In contrast, the other options indicate positive outcomes that are not consistent with the state of staleness. Increased energy levels, muscle gain, and improved sleep are generally associated with a well-balanced training regimen and adequate recovery rather than overtraining. Therefore, recognizing loss of appetite as a consequence of staleness reflects an understanding of how the body responds negatively to excessive training.