Over the last several years, issues like overtraining and relative energy deficiency in sport (RED-S) have become a centrepiece in conversations about distance running. Much of the research surrounding this topic has been focused on its effects on females, specifically athletic amenorrhea (i.e. loss of the menstrual period) and the female athlete triad. Researchers are now looking at how low energy availability affects men, with the focus on one key hormone: testosterone. For male distance runners experiencing a lengthy performance rut, chronically-low testosterone could be a potential culprit.
How does testosterone affect running performance?
Most people think of testosterone as the hormone that allows bodybuilders to get bulging biceps and massive quads, but it also has a significant impact on performance in endurance sports. Of course, it does play a key role in building lean mass, and while distance runners don’t want to be packing on pounds of muscle, a decrease in muscle strength will impair running performance.
Just like women need estrogen to maintain bone mass, men need testosterone to keep their bones strong. For this reason, chronically low levels of the sex hormone could put them at a greater risk for stress fractures. Perhaps most importantly, testosterone helps increase your red blood cell count, which has a direct impact on running performance. The more red blood cells you have, the more oxygen you can carry to your muscles and the longer you can run before having to slow down or stop.
As a side note, if you’re a woman reading this and you’re wondering if low testosterone is something you need to worry about, you can relax. Women do have some testosterone, but they don’t require nearly the amount their male counterparts need, and there has been no research that links low testosterone in women to decreased athletic performance.
How does running affect testosterone?
Distance running (or any other endurance sport) may cause a slight decrease in testosterone levels, but it’s usually not enough to cause health problems or a performance decrease. Chronically low levels of testosterone, then, are a result of overtraining. A 2018 study published in the Journal of Biochemistry and Physiology found that a small percentage of men who engage in regular endurance training (roughly 15 to 25 per cent) have low resting testosterone levels. Most of these men don’t qualify as having a testosterone deficiency, but they are on the very low end of what is considered normal.
Why does this happen? Running, for all of its benefits, puts a lot of stress on your body, especially when you’re doing a lot of volume and intensity. Your endocrine system (which produces and secretes all of your hormones) is particularly sensitive to stress, especially the components that are responsible for reproduction. Basically, when your body is under a lot of stress, it’s going to prioritize the functions that are more essential for life. In this case, reproduction is fairly low on the totem pole, so it’s one of the first things to get the boot.
This is why some scientists believe that extremely low body fat, which is often associated with overtraining, may also play a role in decreasing testosterone levels. Fat cells produce a chemical called leptin, which tells your brain that you’ve had enough food to avoid starving. If your body isn’t producing enough leptin (because you have so little fat), your brain will think you’re starving and shut down the production of testosterone because reproducing is not essential to survival.
What are the signs of overtraining and low testosterone?
The only way to know with certainty that you have low testosterone is to get bloodwork done, which typically won’t happen unless you’re showing symptoms of a possible problem. Signs of overtraining (and potentially low testosterone) could include having trouble sleeping, chronic fatigue, decreased libido and of course, a decrease in performance. Low testosterone can also result in diminished bone mineral content, but unfortunately, this is not a symptom you will notice until you’re sidelined by a stress fracture. For young athletes in their peak reproductive years, chronically low levels of testosterone for an extended period of time can permanently impair fertility.
Hormones are not black and white, and every runner will have varying levels of testosterone. Just because your training partner has higher levels of the sex hormone won’t necessarily mean that he’ll be faster than you, but if you have chronically low testosterone, your performance may take a hit. If you suspect you have low testosterone, talk to your doctor about getting it checked. It is also wise to take a serious look at your training load and how well you’re recovering, and to make some changes if you think you might be overtraining.