(Photo Courtesy of John Blanding / The Boston Globe / Getty Images)

Ryan Hall, one of the great American distance runners of the past decade, announced recently that he is retiring from competition. Hall blamed low testosterone and fatigue so deep and unrelenting that, after years of running more than 15 miles daily, he can now barely manage 12 miles a week. Among insiders, that sounds an awful lot like a mysterious but pervasive affliction broadly known as Overtraining Syndrome — a miserable suite of physiological and psychological symptoms that stalks surprising numbers of endurance athletes, both amateur and professional.

Hall is a famously driven hard-worker who became a stand-out track star at Stanford, where he won the 2005 NCAA Championships in the 5,000 meters. Hall set the American half-marathon record in 2007, and he ran the fastest-ever marathon by an American in Boston, in 2011. But the last few years of Hall’s professional career have been characterized mostly by races that he failed to complete or never even started. Hall dropped out of the 2012 Olympic marathon close to the 11-mile mark, and he withdrew from the New York Marathon in 2012 and 2013, from the Boston Marathon in 2013, and from the Utah Valley Marathon in 2014.

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Researchers have known since the late 1980s that chronic and extreme endurance training has a tendency to lower testosterone levels, causing depression, fatigue, and lack of motivation. More recently, however, exercise-induced low testosterone has been recognized as one of many common biomarkers for a more systemic breakdown: training that is so hard, frequent, and long, and with such inadequate rest along the way, that fitness, performance, energy levels, and mood all fall off a cliff.

To understand how this can happen, it helps to be familiar with the progressive overload principle, which is the basic mechanism behind all athletic training. Put simply, we only get fitter by pushing our bodies a tiny bit harder each workout — running a little further, swimming a little faster, lifting a little more weight. Each new overload depletes our muscle fuel stores, tears down muscle fibers, burns up neurotransmitters, and causes the secretion of various hormones, like testosterone, adrenaline, and cortisol. As we rest after each hard training session, a kind of neuroendocrine recovery system kicks into gear, restocking the fuel in our muscles, rebuilding our muscle fibers, and replenishing depleted hormones and neurotransmitters.

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According to one theory about Overtraining Syndrome, this recovery system can itself get worn out or even permanently damaged, causing the body to lose its capacity to bounce back from exercise. Let’s look at this through the lens of a hypothetical athlete: He pushes himself despite mounting fatigue, still running and lifting weights or doing whatever he does, but he finds his fitness going the wrong direction. The harder he trains, the less fit he gets. The more he powers through swim workouts, the slower his lap-splits become. At night he wakes up repeatedly to find his heart racing. He grows irritable and unhappy, and soon finds himself so tired that he cannot even complete workouts. Being an overachiever, our athlete tells himself that he has to push harder, so he loads up on sugar and caffeine to fight through training sessions when his body is begging for the couch. The most difficult part, given that our athlete has built his entire identity around the positive feelings that come from training hard, is that he finds the entire mechanism of work and reward flipping upside down; now hard training sessions leave him stressed and depressed instead of elated.

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When our overtrained athlete finally hits the wall — and, shortly thereafter, the couch, as depression and fatigue become irresistible — he takes a week off training, but finds that he still cannot sleep properly and that his fatigue will not abate. A week becomes two weeks, then three, then a month. Our athlete’s competitive season is now shot and yet, despite long nights in bed and daily two-hour naps and big healthy meals and almost no exercise, he feels like he has a chronic case of jet-lag, plus mononucleosis, low self-esteem, and maybe the flu.

The only reliable cure for Overtraining Syndrome is rest — as in, near-complete cessation of exercise for weeks or even months — although athletes have been known to experiment with anti-depressants like Prozac. In extreme cases, like the overtraining that afflicted world-champion triathlete Scott Tinley in the 1980s, or, by all accounts, distance runner and current Nike running coach Alberto Salazar, it can last for years, permanently impairing performance and terminating careers.

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It takes a lot to push your body off this big of a cliff — hours a day, generally speaking, for years. But according to professor Jack Raglin, in the School of Public Health at Indiana University Bloomington, studies have found that 34 percent of teenaged competitive swimmers and 64 percent of elite American male distance runners will develop the syndrome at some point in their careers. Individual vulnerability also seems to vary widely, meaning that some of us can get overtraining syndrome on far less training than others. A cursory glance through online endurance-sport discussion forums turns up long threads on the topic, full of anguished testimony from recreational athletes who have been there, and who are desperate to know how long it lasts.

The takeaway? Ryan Hall has almost certainly been suffering worse than he lets on. For the rest of us, though, the bigger news is that overtraining syndrome is real, scary, and waiting around some distant corner for every competitive athlete who doesn’t know when to stop.

By Daniel Duane

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