Why Rest Days Are Important For Long-Term Growth

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Sentience ain’t easy. For athletes, a lot of that difficulty lies in how our brains and bodies develop in different ways.

Our brains can expand to encompass the universe. Grey matter often seems to act like a sponge, but when it should be saturated and can’t absorb another drop, you just get more sponges to play with.

Bones and gristle don’t work that way. Outside of our brains, the processes of stress, recovery and adaptation are playing by much less lofty rules. You get one sponge; use it wisely.

That gap is a major problem for motivated athletes. Distance? The brain can run 100 miles a week without a problem. Workouts? Like that rap song, the brain can work hard every day-ay-ay-ayyyy.

The body follows orders. And all too often, that can lead to stagnation, regression and injury from overdoing it. Here’s a scenario I see all the time. A motivated athlete finishes a workout, let’s say 10 x 3 minutes fast with 2 minutes easy recovery in the context of a 12-mile trail run. As they take off their shoes, they are exhausted. How long do you think it takes for them to be mentally ready to go again?

It varies, but among some athletes, their brains would be ready again in 30 minutes or less. That workout is ancient history in the prefrontal cortex. Meanwhile, the physical stress of the workout has an exponentially longer tail. Even when the brain feels ready to go, the body is working on a different timeline.

So it makes sense that motivated athletes hate rest days. That is time to be working! The competition is getting stronger while I’m sitting on my ass! Why are you treating me like an injury-prone baby?!

I get that feeling. But what I have seen in athletes is that rest days are by far the most important days of the week. Full rest is often essential for strength, speed, endurance and almost everything else that goes into athletic performance.

This article is about reframing rest days for that pesky brain that considers empty spaces lost opportunities. Rest days are not about being cautious and playing it safe. Rest days are about shooting your shot and going all in on your potential.

Rest days are by far the most important days of the week.

The physiology is complex and debated, but here is a basic summary of eight points to think about:

Glycogen Repletion

Consistent training puts the body under relatively constant strain to refill depleted glycogen stores. As glycogen levels go down, there is some evidence that top-end performance decreases even before the tank is fully depleted. And while training in a glycogen depleted state may enhance some adaptations (see this article in the Nutrition & Metabolism journal), doing it chronically increases stress (see this article in the Medicine and Science in Sports and Exercise journal). That can reduce or reverse subsequent adaptations.

Avoiding low energy availability is absolutely essential for long-term growth. Glycogen burns rapidly but refills at a drip, so constant training makes any slip-ups in fueling (even just for a few hours) prohibitively risky. Rest days give athletes plenty of time to fill up the tank. With that extra energy, the body can adapt to the work that was done.

Sex Hormones

Here’s something that won’t be on a running magazine masthead: hard training can hurt your sexual drive and performance. A 2017 article in the Medicine & Science in Sport & Exercise journal found men with higher levels of chronic intense exercise and greater durations of endurance exercise had lower libido. A 2018 Letter to the Editor in the journal Hormones found that men who trained seven hours or more a week had an approximate 30-percent reduction in testosterone levels after five years of training, after which testosterone leveled off. A 2019 article in the International Journal of Sport Nutrition and Exercise Metabolism reviewed the literature on low energy availability from training, finding that it could suppress sex hormones in female athletes.

This point gets back to that brain-body offset. Our brains might be like “I consider myself a voracious sexual beast.” And the chemicals in our nervous system might be like “Umm … I regret to inform you … but no.”

Rest days could improve sex-hormone balance over time, particularly when combined with adequate fueling. That will improve performance on the trails due to the importance of sex hormones for adaptation and health. And it may also improve performance other places. Like the roads. This is a family publication.

Rest days could improve sex hormone balance over time, particularly when combined with adequate fueling.


Cortisol is produced by the adrenal glands in response to stress, which includes most athletic activity due to the hormone’s role in regulating glucose concentration in the blood. Chronic cortisol exposure can undermine almost every element of what makes a sentient human, from cognitive function to athletic performance to body composition.

Cortisol is like that crazy friend you enjoy being around for short periods. “Hey, Jared can really be the life of the party!” But when Jared gets drunk and overstays his welcome, everything goes to hell. “Jared, why are you holding an empty container of lighter fluid? And where’s the cat?!”

Rest days give your adrenal glands a break. Cortisol is probably connected to all of the bad things listed in this article in one way or another, so being 80-percent too safe and over-resting is usually better than being one-percent too risky and pushing the limits of stress.

Adaptation Processes

Think about this question: how does adaptation actually work? While we can scientifically pinpoint important variables (genetics, genetic expression, proteins, molecular pathways, system-wide stress response), we can’t really model every detail as it occurs in the real world. Training for performance is taking an immense amount of physiological complexity, spinning a wheel of chance and saying, “I really think this will work.”

A few weeks and months and years later, we look back and try to connect dots to form patterns that may or may not actually be there. It’s a lot like looking at the stars. If you want to see a man riding a bull, you can probably see that. If you want to see random chaos, you got that too.

Given that we aren’t 100-percent sure how training interventions lead to adaptations over time, the key is to avoid cutting the adaptation processes off altogether. The main way to stop adaptation is to chronically under-recover from stress. Give me an athlete that did a little bit less than they could (whether due to caution or time constraints or an injury) and I’ll bet they can progress more long-term than an athlete that did too much for too long.

Rest days are long-term adaptation insurance. Maybe you’ll sacrifice a very small amount of aerobic adaptations short term (and I think that’s debatable for most athletes). Long-term, the rest investment will pay off massively.

Rest days are long-term adaptation insurance.

Overuse Injuries

The hardest part of being a runner is impact. It’s why this article would be totally different if we were looking at cyclists or swimmers, who may barely need to rest at all. The mere act of moving under load causes significant stress to the musculoskeletal system, even at slow paces. Overuse injuries are often brewing long before they become apparent as discomfort.

Rest days can prevent problems before you even know about them. And all of the variables talked about above can contribute to overuse injuries too. It’s all thrown together into a genetic context that varies heavily based on the individual. There are some people reading this article that were dealt a genetic full house—those people might not have much to worry about with some injuries. But for most athletes, the rest-day insurance can give our genetics the best possible chance to work magic.

For example, my wife and co-coach Megan works with a company called Axgen that provides a genetic test for sports injury risk to athletes. Across massive sample sizes, they have seen that genetics can influence everything from risk of bone stress injury to ankle sprains. Most likely, everything in an athletic life plays by similar rules, mixing genetics with environment and behavior. When in doubt about how complex variables interact, giving the body space and time to build is usually the best bet.

Blood Volume and Cardiac Output

Now we’ll briefly get into three variables that may make rest days less advisable. Blood volume can contract with rest, though it’s debatable how much it will decrease with one day off. In addition, cardiac stroke output (how much blood the heart pumps with each beat) may go through changes as well. However, both variables rebound rapidly, and even with perfect training they reach an upper limit, so you’re not leaving long-term adaptations on the table by having a low-stress day.

Reduced blood volume and cardiac output may be part of the explanation for why athletes sometimes feel tired or sluggish after rest days (along with the neuromuscular variables). Often, that sluggish day precedes a fitness boost the following day, so consider not taking a rest day directly before your harder workouts and races.

Neuromuscular Variables

Neuromuscular economy is a catch-all term I’m using to describe how your brain and your muscles communicate to coordinate the complex task of running. Rest days could reduce muscle tension, essentially slackening the muscle fibers slightly (though the science on muscle tension is not definitive). Rest could also make the movement of running feel slightly unnatural, possibly due to minor changes in the nervous system. If you’re running consistently, you should be good to go during or after your next run (especially if it includes strides).

Cardiac and neuromuscular variance requires athletes to be patient the day after a rest day. Feeling a bit off is OK. That doesn’t mean you shouldn’t rest. In fact, post-rest sluggishness may actually be an essential part of adaptation, wringing out the sponge so you can absorb more subsequently.

Genetic Expression

I am pretty sure that when you don’t know exactly what’s going on, the best answer to give is “epigenetics.” Epigenetics is how gene expression changes depending on the environment, and we don’t really know how it works for athletics, so it’s the best irrefutable response. Why does this workout work? Epigenetics. Why didn’t you do the dishes? EPIGENETICS.

For rest days, you could argue epigenetic influence either way. My guess is that it depends on an athlete’s underlying genetics. My brain is a pretzel now. Let’s move on.

Psychological Variables

Here’s the most important variable. Psychologically, rest days guard against burnout. They give time to step back and practice mindfulness and self-love (not the type connected to sex drive). They stoke the fire. They get an athlete ready to freaking go for the many years that it takes to chase true potential.

Often, athletes will complain about rest taking away their fire. An object at rest and all that jazz. To that, I say that any athlete that doesn’t like rest days is not the type of athlete who needs to worry about their fire. It will be burning tomorrow, and if it’s not, there are deeper psychological issues that are important to explore that go beyond running.

Putting It All Together

I like every athlete to fully rest at least once each week, from top pros to people just starting out. On the rest day, athletes can be active with prehab or other low-stress activities, but no pounding on their legs and no structured aerobic exercise. Instead, the focus is on something much more important: gratitude.

Life is hard. We’re all staring into the abyss and trying to find meaning in the inky blackness that looks back. There’s no universal answer, but I think most spiritual frameworks would say that it’s not about the abyss we are looking into, but the eyes we are staring with.

Our conscious can love and laugh. It can also hate and destroy. Given free reign, I’d bet that the conscious state of most motivated runners will default to compulsion that can ultimately lead to our own destruction, or at least undermine growth.

Rest days are for love and laughter.

Rest days are for love and laughter. They provide the time for our brains to do the work to remember that even though we want to use every second we have to work harder and harder, our bodies don’t operate that way. We’re fragile bones and gristle, after all. And how cool is that?

David Roche partners with runners of all abilities through his coaching service, Some Work, All Play. His book, The Happy Runner, is about moving toward unconditional self-acceptance in a running life, and it’s available now on Amazon.

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