When we're sleeping, our bodies try to take full advantage of the low-energy requiring time of the activity to rebuild our muscles so that our most recent workout pays off. This makes us feel fresh and stronger for our next visit to the gym. 8 hours would be ideal. 6 should be the minimum. It's not uncommon for people to say they can function just fine with just a few hours of sleep. They can function, yes, but they're doing nothing to benefit their bodies. Consistency in sleep deprivation can be a big hindrance in muscle growth and fat loss goals.