Sleep serves many vital functions. For bodybuilders the main functions are growth and mental alertness. Sleep provides these effects directly. Without adequate sleep, time in the gym could be, to a large extent, wasted.
The following are important functions of sleep:
Sleeping for 8-10 hours per night is similar to fasting and this is catabolic to muscle growth. However, eating just prior to sleeping, can help to reverse this process and increase protein synthesis. Protein synthesis does occur under conditions of sleep but it occurs in the gastrointestinal tract, not the muscles.
Muscle is actually broken down under these conditions to provide our stomach with amino acids during the time of starvation. Eating before bed is crucial in offsetting this. Some reports suggest waking up in the middle of the night to eat (nocturnal eating).
Human growth hormone is also released under conditions of sleep. In men, 60% to 70% of daily human growth hormone secretion occurs during early sleep which is typically when the deepest sleep cycles occur. Poor quality sleep can negatively impact human growth hormone levels.
Research suggests that it's during REM (Rapid Eye Movement) sleep that the body is able to: restore organs, bones, and tissue; replenish immune cells; and circulate human growth hormone. Sleep has a profound effect on muscle growth and physical well being.
During sleep energy consumption is lowered: Lowered energy consumption is a biological mechanism for resource conservation. We would need many meals per day (rather than the normal 4-6 for bodybuilders) if we did not get enough sleep.
With bodybuilders, the name of the game is increased size, so energy conservation out of the gym is paramount. Several meals throughout the day also assists growth, and sleep helps to ensure that food is used to replace energy and rebuild muscle (pre-sleep meals and nocturnal eating help to intensify this effect).
Recovery will take a backward step if one does not prioritize sleep, so get to sleep if you want to grow.