I don’t have a scientific background—at least not in the hard sciences—but I’m interested in how my body feels and in the experiences of the athletes I coach. To better understand them, I eagerly study sports physiology. One of my sources of inspiration is the writing of David and Megan Roche, who are also my coaches. I read David’s articles, listen to Megan’s podcasts, and then study the sources they cite; little by little, an informed framework emerges that helps me better interpret my own sensations. So I don’t position myself as an expert, but rather as a passionate and curious coach, seeking solid foundations for the widely held truths about sports training.
Here’s one such “great truth”: “Recovery and rest are part of training.” OK, but why?
Athletes, both seasoned and amateur, often view rest days as wasted time, a missed opportunity for progress, or even a step backward. In reality, regularly scheduled rest and recovery days are essential for any progress—rest helps our entire body, from our cells to our nervous system.
Training without allowing time for adaptation amounts to slow destruction. In the world of endurance sports, there’s a tendency to think that training well means training a lot, or even all the time; but in fact, by leaving no room for rest, we’re slowly wearing ourselves down. Training involves creating a load (often called “stress” in this context); this stress impacts the body (the skeletal-muscular, endocrine, nervous, and psychological systems), which responds by becoming stronger. But you have to give it the space to do so. That’s where planned rest comes in.
The Effects of Continuous Training
Let’s first look at the effects of chronic stress—that is, continuous training—on the endocrine system. A 2018 study in the journal *Hormones* and another 2020 study in the *International Journal of Environmental Research and Public Health* show that testosterone levels drop in male athletes (10% after one year, 30% after several years) who undergo high training volumes. This link between hormones and training is more difficult to study in women due to the menstrual cycle, but there are countless studies showing the relationship between overtraining and severe hormonal imbalances, with the resulting consequences (mood swings, depression, weight gain, anemia, amenorrhea, chronic fatigue, etc.).
A 2019 article in the *International Journal of Sports Nutrition and Exercise Metabolism* describes how even a small imbalance between energy intake and expenditure in athletescan disrupt hormonal regulation and bone density, increase the risk of injury, and reduce adaptation to training load. This is a compelling reminder that it’s important to eat when exercising; the effects on the endocrine system can be felt even during a single day of fasting or insufficient caloric intake (see a 2017 study on female athletes and a 2018 study on male athletes).
Exercise also increases cortisol levels (commonly known as the stress hormone); without rest periods, maintaining elevated levels will have various consequences, both physically and psychologically.
Key Takeaway
: For our workouts to be effective, we need a stable endocrine system. If we keep our foot constantly on the gas pedal, the engine will burn out.
The Effects of a Lack of Rest on the Musculoskeletal System
Most of our sports injuries begin with tiny changes in our connective tissues or bones. At this early stage, this is often a stimulus for the body to repair and strengthen itself—and that’s the positive effect of training. Often, a single day of rest is enough to trigger this positive adaptation and come back stronger. But if we ignore the early warning signs of injury, then the day off we denied ourselves at one point turns into weeks or months of forced rest. Taking one rest day per week is a way to prevent this kind of scenario; it gives you time to heal from micro-injuries and become more resilient.
This 2016 study published in *Physiology Reports* shows that when an athlete takes rest days based on their creatine kinase levels (which help assess post-workout muscle damage), that person not only avoids injury but also improves their endurance speed.
Key takeaway
: Rest days planned in advance support adaptation and prevent periods of forced rest.
The Effect of Overtraining on the Nervous System and Stress
Failing to account for physical and mental stress (the body doesn’t distinguish between the two—we recover less effectively from a workout when we’re mentally stressed) can lead to overtraining syndrome. So far, I’ve referred to overtraining as a lack of rest; it is also the clinical term for a state of chronic fatigue, in which the body can no longer recover and performance declines (see the article in *Current Sports Medicine Reports*). As mentioned earlier, all types of stress are absorbed and processed by the nervous system. When in doubt—if you’re feeling stressed or have low energy—rest instead of going through with your scheduled workout.
Key Takeaway
: “Pushing yourself” to the limit on a day when you feel tired can pose risks to your long-term health and performance.
In summary
Rest once a week (real rest, not intense sessions of DIY, moving, cleaning, or gardening). Be proud of your rest days. Training doesn’t make champions—recovery does.
Note: This article is largely inspired by David Roche’s excellent piece and is used here with his permission.