Growth hormone (GH) is an anabolic chemical messenger released by the pituitary gland during exercise and SLEEP. This is critical for proper recovery, cell repair, and muscle growth. The largest amount is released after the first two hours of slumber, then tapering off throughout the night. In short, this is why interrupted sleep or sleep deprivation will prevent proper recovery, resulting in mental and physical fatigue. Ladies follow suit; even if muscle building isn't your goal, GH also enhances the utilization of fat and helps maintain a healthy weight, among other things.
Tip: Either limit or avoid carbohydrates before bedtime. Carbs very well may blunt this release of GH