You see those guys that are always in the gym? I mean, always in the gym... Everyday. For some reason they're not making any process. Well consistency is clearly not the issue, it's a lack of rest. The importance of rest days is sometimes overlooked in gym goers, especially new ones. It is rest that makes you stronger, because it is the rest that allows the muscles that you have broken down to heal and recover. It is during sleep where Growth Hormone (GH) levels are at their highest. Physiologic improvement in bodybuilding can only occur during the rest period following hard training. This is also why consuming the proper foods and supplements immediately following such training is key. If you don't ever take a rest day your body will never fully heal and you will eventually not only stop improving, but become weaker.