Typically, you think of resting as wasted time because it’s time when you aren’t burning any calories or building muscle. However, this isn’t the case. Your body requires rest days just as much as it needs cardio and resistance training days.

Replenish Muscle Glycogen Reserves

Your skeletal muscles retain glycogen — the stored form of glucose. During exercise, those glycogen particles break down. Your body uses them for energy before it breaks down fat. As your body uses those reserves, you’ll notice that you experience muscle fatigue.

Through rest, your muscles have an opportunity to rebuild their supplies. In return, you’re ready for your next workout. For this reason, you’ll also be able to work out longer the next time without experiencing muscle fatigue as soon when you give your body a break.

Repair Muscle Tissue

Throughout physical activity, your muscles contract and retract. This process causes microscopic tears in the tissue, although the exact toll depends on the workout’s intensity and the types of exercises you perform. These tears are the reason you have soreness after you exercise.

On rest days, your body sends fibroblasts — cells that form connective tissue — to the site to repair the damage. Therefore, rest days give your muscles a chance to recover between workouts.

Prevent Injury

If you over-exercise, you push your muscles and other soft tissue beyond what they can handle. This repetitive stress may result in an injury that could keep you from exercising or even completing everyday tasks.

One of the more common repetitive stress injuries is tendinitis, which occurs when you overwork a tendon and cause it to become inflamed. When you give your body a rest, you give those tendons and other soft tissue time to heal.

Give Your Mind a Break

While you think of over-exercising as wearing you out physically, it takes a toll on your mind as well. Functional magnetic resonance imaging has shown a connection between overworked athletes and slower response in the lateral prefrontal cortex. This part of the brain is responsible for problem-solving, planning and reasoning. Because of this, if you overexert your mind exercising, you’ll be more at risk of experiencing an injury and making poor decisions in general. You might also overwork your brain to the point that you have difficulty falling asleep due to the adrenaline and cortisol produced when you overexert yourself. 

You may also suffer from depression and anxiety if you’re isolating yourself from your family and friends to exercise. Your rest day gives you time to catch up with those you love and prevent this from occurring.

Prevent Muscle Mass Loss

When you participate in moderate-to-high-intensity exercise, your body burns stored carbohydrates for fuel. That’s why you may feel sluggish after a workout. When your body runs out of reserves, it uses protein for fuel instead. A rest day can give your body time to replenish your energy bank and prevent muscle loss.