Ask any professional body builder what they do when they’re not working out, and you’ll quickly find out it has nothing to do with exercise. In fact, it’s quite the opposite. Fitness buffs use their downtime to relax — as in, their muscles.

The reason for this is that the truth behind building muscle has a lot less to do with “building” than many people think. When we work out, we may feel that our muscles are growing larger and harder as we work, but in truth this is just a temporary expansion due to the current stress on the muscle.

Part of the reason for this expansion is that when we work out, we are actually causing our muscles to tear. That might sound bad, but it surprisingly isn’t. Believe it or not, in order to “build” muscle, it has to first broken down.

Real muscle building doesn’t occur until after the workout. In a similar fashion to a tear in your skin healing and scarring over, the tears in your muscles scar over, causing the muscle to become thicker, larger, and stronger. This is why it is so important to body builders that they get plenty of rest; the more rest time they have, the more time is dedicated to their muscles actually building and properly healing before the next workout and tearing-rebuilding cycle.

If you see a body builder in the gym every single day, take a look at what muscles he or she is working. You will notice that he or she does not work the same muscle groups every day. They rotate days so that each group has an appropriate amount of rest time before being worked on again.

You don’t have to be a body builder to understand the necessity of muscle rest, though. Even if you are not necessarily trying to “bulk up” (you may be trying to do just the opposite!), imagine the damage you could do to your muscles if you haven’t allowed the tears from your last workout to properly heal.

When your muscles are sore or feel exhausted, even though the rest of your body feels fine, it means that they have not fully recovered yet. Stretching assists the muscle healing process by improving blood flow to the muscles, which is why it is so important to stretch not only before each workout, but after as well.

So how much is enough — rest that is? The period of rest will vary greatly from person to person, and from muscle group to muscle group. In general, abdominal muscles are the quickest muscles to recover, and can be worked out every day (apologies to all those who were praying for a break from abdominal exercises!).

Legs are next on the list, meaning that you can go walking, running, biking, etc. every other day safely. It starts to get tricky when you get to the arms, chest, and back. Play it safe and work each of those muscle groups just once a week, and you’ll be sure to be giving those muscles plenty of recovery time.

Muscle rest is essential to your safety while working out, as well as your health in general; make sure not to ignore it, and you will see the results you are looking for while feeling your best.