Technically, you don’t grow in the gym, you grow most when your body is at rest. Adequate sleep also helps keep Cortisol (a hormone that can cripple your efforts to gain muscle and loose body fat) at bay. Ensure 7-9 hours. Also keep in mind that the hours of sleep before midnight are especially beneficial, so there is in fact a difference between sleeping from 10pm-6am versus 1am-9am.