Pushing through a hard workout requires mental toughness and stamina, which means that physical activity is not only hard on your body, it can really fatigue your brain as well. Spending a day away from your typical training can give you a psychological break from exercise while also helping your mind relax, allowing it to recover along with your muscles.
This is where the magic happens, when we rest our muscles recover and grow back stronger.
Taking a rest day can help your body properly replace the energy stores (glycogen) in your muscle cells so that you have a full battery for your next hard workout.Often times feeling sluggish or drained at the end of a workout could mean your glycogen levels are depleted.
Avoiding rest days can set you up for things like repetitive stress injuries or overtraining, which will eventually force you to take some rest days. This might leave you away from your favorite exercise routine longer then you would like.
Last tip: A well-designed exercise program will help you meet your goals and include adequate rest to fully recover from the stresses of hard exercise.