Which of the following can negatively impact an athlete's sleep quality?

High-stress levels can significantly undermine an athlete's sleep quality due to the direct impact of stress on the body's physiological responses. When an athlete experiences elevated stress, the body produces higher levels of cortisol and adrenaline, which can lead to increased heart rate, heightened alertness, and difficulties in relaxing. These changes create an environment that can delay sleep onset and reduce overall sleep quality, making it harder to achieve restorative sleep necessary for optimal recovery and performance. Other factors such as regular physical activity, relaxation techniques, and a well-balanced diet generally promote better sleep quality, illustrating the contrast with how high-stress levels can inhibit restful sleep.