Sleep and Athletic Performance: Your athletic performance depends not only on the way you train but also on the way you rest. That's why fitness coaches from around the world now pay more attention to the amount of sleep you get. After an intense training session, the body requires rest for your gains to show. During the workout, the muscle cells break down, which gets repaired when we sleep. So it's really important to get adequate sleep and take regular naps for muscle gain and fat loss.