During sleep your nerves, muscles, bones, and immune system all recover from the stresses of daily life and undergo repair, restoration and growth (in a process called anabolism - the metabolic activities that build new cells). This restoration process occurs at specific times during your sleep cycle. When you sleep you go through 5 sleep stages:
Stage 1: The lightest stage occurs as you start falling asleep and lasts about 5 – 10 minutes.
Stage 2: Still light sleep lasting about 30 minutes but transitions you towards a deeper sleep.
Stages 3 – 4: During these stages you move into deep sleep or slow wave sleep lasting between 10 and 30 minutes where brain activity decreases and your body begins restoring itself mentally and physically.
Stage 5: REM or Rapid Eye Movement Sleep, where you brain becomes more active and you dream. REM sleep can last from 5 minutes anywhere up to an hour and your body and mind continue to replenish their reserves through this stage.
During a night’s sleep your body will cycle through stages 3, 4 and 5 several times, and it is these stages where you are properly rested and most muscle growth occurs. The quality of sleep during these stages has a direct impact on the amount of muscle you will build. More good quality stage 3, 4 and 5 sleep means greater muscle gains, but only if you have a ready supply of protein in your system.