Key takeaways
Testosterone raises haemoglobin, which helps explain part of the sex difference in VO2max, but small changes within the normal male range matter little
Years of high-volume endurance training can lower resting testosterone, and low energy availability is a key cause to rule out
Sleep, enough food, a healthy body fat level and strength training support normal testosterone far better than over-the-counter boosters
Testosterone has a reputation as the "strength hormone", but it also matters for aerobic fitness, mainly through the blood. At the same time, endurance athletes are one of the groups most likely to have low testosterone. Here is what the research says about both sides, and why a supplement aisle "booster" is rarely the fix.
Does testosterone affect VO2max?
VO2max is limited mainly by how much oxygen the heart can pump and the blood can carry (see what limits VO2max). Testosterone acts on the second part.
The haemoglobin link
In a trial in older men, 6 months of testosterone gel raised haemoglobin and haematocrit by roughly 7–10%, by stimulating erythropoietin (EPO) and lowering hepcidin, the hormone that restricts iron absorption (Bachman et al., 2014). More haemoglobin means more oxygen delivered per heartbeat, which is why haemoglobin mass is closely tied to VO2max.
This is also part of the sex difference. A review by Handelsman and colleagues (2018) found a dose-response relationship between circulating testosterone and both muscle mass and haemoglobin, and concluded these largely account for an ergogenic advantage of at least 8–12% in men (see VO2max norms by age and sex).
The important caveat: that is the gap between female and male levels, or between a deficient man and a treated one. Small shifts within the normal male range have far less effect.
Low testosterone in male endurance athletes
The exercise-hypogonadal male condition
Anthony Hackney's group described men who, after years of heavy endurance training, show persistently low resting total and free testosterone without the rise in LH that would normally signal the body to make more. Hackney (2008) called this the "exercise-hypogonadal male condition" and noted that it seems limited to men training for years, is not highly prevalent, and may be either a dysfunction or an adaptive readjustment of the hormone axis. A later review (Hackney, 2020) discussed whether it is a problem at all, since very active men in non-industrial populations also have lower testosterone.
How common is it? In 196 competitive runners training at least 7 hours or 80 km a week, Hackney and Lane (2020) found androgen deficiency in 15.3%, versus 5.6% of matched non-exercising men.
Does low T hurt performance?
Not necessarily. In a small study of an 18-week intensive endurance programme, resting testosterone fell by 25–45%, yet running performance improved by 18.6% (Hackney and Hooper, 2020). The authors cautioned that reproductive and bone health may still suffer even when performance does not.
Low energy availability and RED-S
The most important cause to rule out is not eating enough for the training load. The 2023 IOC consensus statement (Mountjoy et al.) defines Relative Energy Deficiency in Sport (REDs) as impaired physiological or psychological function caused by problematic low energy availability, in male as well as female athletes, and highlights growing evidence on how it affects men.
In national and world-class distance athletes, Heikura and colleagues (2018) found that men with testosterone in the lowest quartile of the reference range also had lower thyroid hormone, and low testosterone was associated with more bone injuries. Their conclusion: reproductive hormones may be a more practical marker of energy deficiency than trying to calculate intake and expenditure. Cyclists, rowers, combat athletes, distance runners and jockeys are among the higher-risk groups (Burke et al., 2018).
If your testosterone is low and you train a lot, the first questions are about food, carbohydrate and recovery, not supplements. Women face parallel issues with the menstrual cycle; see VO2max, the menstrual cycle and menopause.
Sleep, body fat and strength training
- Sleep. Restricting young healthy men to 5 hours a night for one week lowered daytime testosterone by 10–15% (Leproult and Van Cauter, 2011). See VO2max and sleep.
- Body fat. In a meta-analysis of 24 studies, weight loss in men with obesity raised testosterone, and the more weight lost, the bigger the rise (Corona et al., 2013). See VO2max and body weight. For lean athletes, the risk runs the other way: chasing race weight can cause low energy availability.
- Strength training. Heavy resistance exercise raises testosterone briefly after sessions, though resting levels often do not change with training (Kraemer and Ratamess, 2005). It builds muscle and bone regardless; see strength training for runners.
- Training load. Easy volume and planned recovery, as in 80/20 training, and watching resting heart rate and HRV can help spot overload early.
Boosters versus medical testosterone therapy
Over-the-counter "testosterone boosters" mostly do little for healthy men:
- Zinc restores testosterone only if you are deficient.
- Boron rests on one tiny week-long study.
- Tongkat ali shows an effect mainly in men with low testosterone, with quality concerns.
- Fenugreek may cause a small rise in total testosterone, with very low certainty.
- D-aspartic acid failed in trained men.
None raises VO2max. Worse, booster products can be contaminated: Geyer and colleagues (2004) found 14.8% of 634 supplements contained undeclared anabolic steroids, which under WADA's strict liability rule is the athlete's problem. Competitors should stick to Informed Sport or NSF Certified for Sport products. Our supplements guide covers what does help endurance.
Medical testosterone therapy is a different thing entirely. The Endocrine Society guideline (Bhasin et al., 2018) recommends diagnosing hypogonadism only in men with symptoms and consistently low morning fasting testosterone on repeat tests, then looking for the cause before treatment. Therapy is prescribed and monitored by a doctor, because it can push haematocrit too high and suppresses sperm production. In sport, testosterone is prohibited at all times under the WADA Prohibited List, and athletes with a genuine medical need must apply for a Therapeutic Use Exemption.
The bottom line
Testosterone supports VO2max through haemoglobin, but healthy men gain little from nudging it within the normal range. If you have symptoms such as low libido, erectile problems, persistent fatigue, low mood, frequent injuries or stalled progress, see a doctor and get tested, and review your energy intake and sleep first. For fitness itself, training is still the lever; see how to improve VO2max.
This article is not medical advice.
Frequently asked questions
Does testosterone affect VO2max?
Yes, indirectly. Testosterone stimulates red blood cell production and raises haemoglobin, which carries oxygen, and higher male testosterone is part of why men have higher VO2max on average. Normal variation within the male range has a much smaller effect.
Can endurance training lower testosterone?
In some men, yes. Hackney described an exercise-hypogonadal male condition in men who have trained heavily for years, and a study of 196 runners found androgen deficiency nearly three times as often as in matched non-exercisers.
Do testosterone boosters work?
Most do little in healthy men. Zinc helps only if you are deficient, tongkat ali and fenugreek show small or uncertain effects, and some booster products have been found to contain undeclared steroids.
Should athletes take testosterone?
Only if a doctor diagnoses hypogonadism and prescribes it. Testosterone is banned in sport at all times, and it carries risks such as high red cell counts and suppressed fertility.
Sources
- Bachman E, et al. Testosterone induces erythrocytosis via increased erythropoietin and suppressed hepcidin: evidence for a new erythropoietin/hemoglobin set point. J Gerontol A Biol Sci Med Sci, 2014.
- Handelsman DJ, Hirschberg AL, Bermon S. Circulating testosterone as the hormonal basis of sex differences in athletic performance. Endocr Rev, 2018.
- Hackney AC. Effects of endurance exercise on the reproductive system of men: the "exercise-hypogonadal male condition". J Endocrinol Invest, 2008.
- Hackney AC. Hypogonadism in exercising males: dysfunction or adaptive-regulatory adjustment? Front Endocrinol, 2020.
- Hackney AC, Lane AR. Increased prevalence of androgen deficiency in endurance-trained male runners across the life span. Aging Male, 2020.
- Hackney AC, Hooper DR. Reductions in testosterone are not indicative of exercise performance decrement in male endurance athletes. Aging Male, 2020.
- Mountjoy M, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). Br J Sports Med, 2023.
- Heikura IA, et al. Low energy availability is difficult to assess but outcomes have large impact on bone injury rates in elite distance athletes. Int J Sport Nutr Exerc Metab, 2018.
- Burke LM, et al. Relative Energy Deficiency in Sport in male athletes: a commentary on its presentation among selected groups of male athletes. Int J Sport Nutr Exerc Metab, 2018.
- Leproult R, Van Cauter E. Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA, 2011.
- Corona G, et al. Body weight loss reverts obesity-associated hypogonadotropic hypogonadism: a systematic review and meta-analysis. Eur J Endocrinol, 2013.
- Kraemer WJ, Ratamess NA. Hormonal responses and adaptations to resistance exercise and training. Sports Med, 2005.
- Bhasin S, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab, 2018.
- Geyer H, et al. Analysis of non-hormonal nutritional supplements for anabolic-androgenic steroids: results of an international study. Int J Sports Med, 2004.
- World Anti-Doping Agency. The Prohibited List (S1 Anabolic agents).