If you think all the progress you make fitness-wise occurs while you’re actually in the gym, think again. Turns out, you make gains when you give your body the rest it needs.
Here, experts break down what happens in your body when you take a recovery day — and how taking days off from the grind ultimately helps you become a fitter, stronger individual.
It probably comes as no surprise your muscles have lots of recovery work to do when you take a day off from training.
“Your muscles are constantly in a state of either breaking down or building up,” explains physical therapist William Kelley, DPT, athletic trainer and certified strength and conditioning specialist. When you push your body during workouts, you essentially create micro-tears in your muscle fibers. In the 24–48 hours that follow, your muscles repair — and grow larger and stronger — through a process called muscle protein synthesis. (Your body uses the protein you eat to make this happen.)
Muscle protein synthesis can only occur during rest. “If you’re not recovering, you just always are fighting to get back to baseline,” Kelley says.
Even if you don’t feel sore after a challenging workout, your muscle tissue still sustains damage and needs to heal, adds Max Castrogaleas MA, certified strength and conditioning specialist and, exercise physiologist at New York City’s Hospital for Special Surgery.
In addition to physically rebuilding your muscle fibers, rest also allows the cells in your muscles to restock the fuel they need for you to perform during your next workout. First, there’s glycogen, a form of stored sugar that acts as a “sustained energy source for when you need to perform for longer periods of time,” Kelley says. Then there’s creatine phosphate, a compound we get from red meat our muscles use to power quick, explosive movements.
Just as your muscles take a hit during exercise — and need to do some renovating on rest days — so do your connective tissues, such as tendons.
Think of these tissues — which transfer the forces your muscles produce to your bones so you can move your limbs — like ropes, Kelley says. “During recovery, these ropes thicken and strengthen, so you can pull harder on them without worrying about them fraying or tearing.”
Unlike muscles, tendons are made primarily of the protein collagen (which you get from food sources like bone broth) and shuttle that protein in to repair damaged tissue and increase overall strength.
Though you may not feel soreness in these tissues, the micro traumas they sustain during strenuous exercise can cause swelling you can’t see, which may leave your joints feeling tight and tender, says Castrogaleas.
Your nervous system, the electrical network that connects your brain to the rest of your body, plays a bigger role in fitness than many people realize. After all, it’s your nervous system that signals your muscles to contract when needed.
When you exercise, “you stimulate your nerves to move a muscle or perform a task or do something coordinated,” explains Kelley. Then, when you rest, your body strengthens the pathway between that signal and movement (called a ‘motor connection’) so you can do it more efficiently next time.
“If, however, you jump from stimulus to stimulus, your body never quite forms that pathway properly,” he says. The result: You don’t improve at a certain move as quickly as you could.
Though you might not see any similarities between exercise and an obnoxious email from a co-worker, your body considers both stressors.
In fact, tough workouts can boost our production of the stress hormone cortisol, as well as the other adrenal (or ‘fight or flight’) hormones epinephrine and norepinephrine, explains Castrogaleas. “These hormones increase our heart rate and blood pressure so we feel a surge of energy when we need it.”
While these hormones come in handy during a HIIT session, you certainly don’t want them jacked up all the time.
When too high too often, these hormones — especially cortisol — can affect our sleep, make us hungrier and contribute to weight gain, says Kelley. (They can also contribute to athletes feeling stale or ‘overtrained.’)
That’s where rest days come in: “Recovery days give your cortisol the opportunity to settle back down to baseline,” Kelley says.
Rest also allows your body’s natural ‘steroids,’ IGF (aka insulin-like growth factor) and growth hormone, to step in and do their jobs. “When you experience muscle breakdown, your body produces these hormones to help it repair and grow stronger,” Kelley explains.
In the long run, supporting balance between your stress and growth hormones helps your body adapt and perform more efficiently.
The lymphatic system, which essentially functions as your body’s sewer system, gathers waste products from throughout your body so they can be eliminated. Exercise creates a lot of these waste products, so your lymphatic system kicks into high gear during recovery.
“When you take a rest day, you give your lymph vessels a chance to drain back toward lymph nodes, which disperse lymph fluid into your circulatory system to be processed by your kidneys and kicked out of the body,” Kelley says.
Your heart’s ability to make small heart rate adjustments in response to different stimuli, known as heart rate variability (HRV) has become a buzzy indicator of recovery recently.
In a perfect world, your ticker would quickly pick up its pace to meet the demands of different intensities of exercise — and then settle back down fast. Go hard day after day, though, and “it takes more and more of a stimulus to get your heart rate up,” explains Kelley. Essentially, your heart, too, fatigues.
According to Kelley, recovery days allow the electrical wiring and chemical balance that makes your heart beat to reset. This then re-sensitizes your HRV, making you better-prepared to tackle whatever challenges you push your body through in the days ahead.
Physiological adaptations aside, rest also just does your soul good. “The constant grind can feel never-ending and monotonous,” Kelley says. “If you walk into the gym and groan instead of feeling motivated and excited, that’s a clear indicator that you need to rest.”
When you take regular breaks from training hard, you ward off mental fatigue, give yourself the opportunity to enjoy more leisurely activities (like neighborhood walks or pickup basketball), and ultimately feel more motivated the next time you hit the gym hard.