I teach a class called Metabolic Effect, and this is my spiel at the beginning of each class:
“Welcome to Metabolic Effect! The purpose of Metabolic Effect is to rest. If you are doing this class correctly, you will be resting just as much as you are working out. The goal of this work is to push yourself as hard as you can during the exercises to the point where you need to rest, take that rest, rest completely, and then get back into it when you are ready.”
What is the reason for this? Some research has show that exercise of a high intensity is extremely beneficial. However, without bouts of rest, you would only be able to do a very short amount of intense exercise. Rest is needed to reset the body. You can read more about the theory and physiology behind that here.
Rest is also important after exercise. After a stretch of challenging work outs, the body needs the chance to recover. During work outs, a few different things happen. First, your muscle tissue breaks down in response to the stress placed upon it, whether that be through running, weight lifting, or some other form of exercise. These are tiny, tiny microtears. In response, your muscles repairs that muscle and makes in stronger in order to sustain the same stress next time. This is how your muscles get stronger. This is also why you need to progressively increase your work load–your muscles adapt to the stress you put on it. If you don’t increase the work load (weight, distance, etc.) then you will plateau. However, if you do not allow your muscles the time to repair those microtears, it will lead to injury, fatigue, and ultimately overtraining. Overtraining=bad!
Rest is also important mentally. Have you ever tried a lifestyle behavior change and done PERFECTLY the first 10 days and then you reach a certain point where you’re sick of it and just ruin the whole thing? You eat a wonderfully clean diet and then BAM!! Hello grilled cheese, brownies, french fries, cake, ice cream, pizza, etc. It all goes to hell. Give yourself a rest day as a mental AND physical rest from your work outs to avoid physical and mental burn out.