According to ABC News, sleep affects athletic performance because getting sufficient sleep helps an athlete to focus mentally and recover from training. Being mentally focused allows an athlete to prepare, and an athlete obtains the full benefits from his training during sleep.
ABC News explains that when an athlete trains during the day and his body gets tired, it is very important that he gets enough sleep in order for his body to recover completely and adapt to the training performed. According to WebMD, sleep deprivation may cause the athlete to have less energy, an inability to make wise decisions, slower and less accurate reflexes, as well as high levels of cortisol. Cortisol is the stress hormone that can impede healing and make an athlete more prone to injuries.