That’s not to say that exercise and nutrition aren’t important when it comes to building and maintaining muscle. “When I’m working with someone who’s really trying to build lean muscle mass, I always remind them that you have to eat protein macros, you have to lift heavy, and you have to get quality sleep,” she explains. “You can’t build healthy muscle mass without all three.”

With that in mind, it’s common to skimp on the sleep part of the equation, but Thurlow recommends flipping the script. After all, sleep is necessary to restore the body; and deep sleep (also known as stage 3 sleep or slow-wave sleep) promotes muscle and tissue growth along with cell repair.

Studies have even shown that people with low muscle mass are more often report very poor sleep efficiency1. Another study showed that even one night of sleep deprivation is enough to decrease in muscle protein synthesis2 in young healthy males and females. Essence? Catching Zzz’s is very, very important for building muscle—just as important as strength training and proper nutrition, Thurlow would say.