Does Running Lower Testosterone? What 30 Years of Research Shows

Running is one of the most popular forms of exercise on the planet. It supports cardiovascular health, mental wellbeing, and a healthy body composition. But a persistent concern circulates in fitness communities: does running lower testosterone? The honest answer, as with most things in exercise science, is that it depends on how much you run, how long you have been doing it, how well you fuel, and how well you recover. This article summarizes what the published research does and does not show. It is educational and not medical advice.

Volume Matters, but There Is No Exact Threshold

Decades of research on endurance athletes and hormones point in a similar direction: some men with long histories of high-volume endurance training show lower resting testosterone than untrained men. In the 1984 JAMA study mentioned above, runners logging at least 64 kilometers per week had significantly lower total testosterone and prolactin than sedentary controls, while other hormones, including cortisol and luteinizing hormone (LH), were similar.^[1] A 1988 study found the same direction of effect, with mean total and free testosterone significantly lower in endurance-trained men than in untrained men.^[2]

The findings are not uniform, and they do not tell us where a safe line sits. In a 1986 study of six highly trained marathoners running 125 to 200 km per week, plasma testosterone was similar to controls, even though the runners showed fewer and smaller LH pulses, a sign of altered signaling from the brain.^[6] Reviews by Hackney and colleagues state that the time course and the amount of training needed to produce lower testosterone remain unresolved^[3], and that the pattern seems limited to men who have trained persistently for years and is not highly prevalent.^[4]

One more caveat: the studies above focus on well-trained endurance athletes. We did not find controlled data showing that recreational running at 20 to 40 kilometers per week lowers or raises testosterone. Figures like “56 kilometers per week” that circulate online are best treated as rough rules of thumb, not research-derived cutoffs.

The Cortisol Question: Plausible, Not Proven

A popular explanation is that endurance training raises the stress hormone cortisol, which then suppresses testosterone. The first half of that idea is well supported: in a controlled study of 12 active men, 30 minutes of exercise at 60 and 80 percent of VO2max raised circulating cortisol by roughly 40 and 83 percent, while exercise at 40 percent of VO2max did not raise it.^[7] The second half is less certain. In both of the runner studies above, resting cortisol did not differ from controls, and the 1988 authors concluded that cortisol was not the cause of the lower testosterone they saw.^[1,2] The mechanism is still debated and is postulated to involve the hypothalamic-pituitary-testicular axis.^[3,8]

This is not unique to running. Any pattern of heavy training without enough recovery can disturb hormones. Our full breakdown of overtraining syndrome and testosterone covers the warning signs and recovery strategies. For background on how stress physiology fits in, see stress, cortisol, and testosterone.

Endurance Runners vs. Sprinters: What Can We Say?

It is tempting to contrast marathoners with sprinters, with sprinters coming out ahead hormonally. The research does not support a clean story. In the sprint study we found, 96 men (endurance-trained, strength-trained, and untrained) performed five 10-second all-out sprints, and the researchers saw no significant changes in salivary testosterone or cortisol in any group. They suggested that the exercise volume may simply have been too low to provoke a response.^[9] So while short sprint intervals are a time-efficient way to train, current research does not let us say they raise testosterone. For a broader look, see our article on HIIT versus weight training.

Low Energy Availability and Male Runners

Relative energy deficiency in sport (RED-S, now often written REDs) was first described in female athletes and is now recognized in men too. The International Olympic Committee's 2023 consensus describes a syndrome of health and performance problems in female and male athletes who take in too little energy relative to what they expend, and notes growing data on its impact in males.^[10]

A 2023 mini-review of male endurance athletes found that low energy availability occurs in this group and correlates with lower testosterone, lower bone density, and lower resting metabolic rate.^[5] Hackney has proposed that exercise-related low testosterone in men can arise from low energy availability or from excessive training load, can be transient, and often resolves with appropriate intervention.^[8] A clinical review likewise recommends nutritional intervention and training modification when low testosterone with symptoms (fatigue, sexual dysfunction, low bone density) is found in an athlete.^[11]

This suggests that for some high-mileage runners, the issue may be less about running itself and more about whether food intake keeps pace with training. If you suspect this applies to you, a doctor or sports dietitian can help you work it out. Do not try to diagnose it yourself from symptoms alone.

Practical Takeaways: A Sensible Way to Think About Mileage

Because no research-derived threshold exists, it is more useful to watch signals than to chase a number. The signals that matter most are consistent: how you recover, how you sleep, how your energy and libido hold up, and whether you are eating enough for the work you are doing. Most recreational runners who sleep adequately, eat enough, and allow recovery between hard sessions are not in the population these studies describe.

If your mileage is climbing toward the levels seen in the studies above (64 kilometers per week and up), if you are training in a calorie deficit, or if you are noticing persistent fatigue, low libido, or reduced morning erections, speak with a doctor. They can test your hormones and look for other causes before you change your training.

How to Program Cardio Sensibly

Resistance work still earns its place in a runner's week for muscle and bone health, even though a meta-analysis in men aged 60 and over found it did not significantly change basal testosterone.^[12] A man who runs a moderate amount, lifts weights twice a week, trains with compound movements, eats enough, and sleeps well is following the habits most consistently associated with good overall health. If you enjoy running and want a lower-stress option, consider zone 2 cardio for part of your week. The real risk lies in a “more is better” culture where weekly mileage becomes a point of pride rather than a variable to manage.

The Bottom Line

Running does not categorically lower testosterone. Some men with long histories of high-volume endurance training show lower resting testosterone than untrained men, and low energy availability appears to play a role. No exact mileage threshold has been established, and the pattern is not common. Moderate running supports cardiovascular health and general wellbeing.

If you are a recreational runner, the research summarized here gives you little reason to worry, as long as you fuel and recover well. If you are training for marathons or ultra events, pay close attention to nutrition, sleep, and recovery, and talk to a doctor if you notice symptoms. You might also try rucking or sprint intervals and resistance training to diversify your training rather than simply adding more miles.

How Thrive Helps

Thrive is a wellness app that helps you track your training volume, recovery, sleep, and daily habits in one place so you can spot patterns over time. It is a habit tracker and educational tool, not a medical device, and it cannot diagnose or treat any condition. Try Thrive free and build a routine that balances fitness with recovery.