How does testosterone build muscle?

Crouch and Defoe, Ant and Dec, testosterone and muscle mass – some things just go together. We're sure about the strike partnership and Geordie duo, but is the link between muscle mass and testosterone justified? Strong evidence says it is.¹

Here's how the link works, and what it means for your training.

What is testosterone?

Testosterone is a sex hormone that affects far more than what happens in the bedroom. In men, it helps regulate sex drive, bone mass, fat distribution, muscle mass and strength, and the production of red blood cells and sperm.² Healthy testosterone levels underpin a healthy body.

How testosterone builds muscle

Training damages your muscle fibres. Your body repairs and rebuilds them through muscle protein synthesis, and testosterone increases the rate at which that happens.¹ More synthesis means faster recovery and better conditions for growth.

Within the healthy range, that's the mechanism working as it should. Pushing testosterone beyond it isn't a shortcut to a muscular physique, and it comes with real risks. Diet and training still decide your results.

Can you build muscle with low testosterone?

Yes. Resistance training and a protein-rich diet still work. But testosterone deficiency can make progress harder: low levels are linked with reduced muscle mass and strength, along with the fatigue and low motivation that keep you away from the gym.²

If that sounds familiar, skip the guesswork. A testosterone blood test shows exactly where you stand.

How can I increase my testosterone levels?

It depends on why they're low. If a blood test confirms testosterone deficiency, testosterone replacement therapy (TRT) is an effective, clinician-led treatment. Men typically notice more energy, a stronger sex drive, and gains in muscle strength over time.³

If your levels are normal and you want to look after them, start with the basics: a testosterone-friendly diet and regular exercise. Testosterone Support contains nutrients linked to the maintenance of normal testosterone levels, including zinc and vitamin D. It isn't a treatment for testosterone deficiency, though. If you think your levels are low, get a diagnosis first.

Does building muscle increase testosterone?

To a point, the link runs both ways. High-intensity resistance training can raise testosterone levels, though the effect is often short-lived, and regular exercisers tend to have healthier baseline levels than sedentary men. Endurance training, on the other hand, can lower them. For the full picture, read our guide to exercise and testosterone.

How else can I build muscle?

The tried and tested way: lift weights, eat enough protein, and stay consistent. The details matter (how heavy, how many reps, how often), but any well-structured resistance programme will move you forward.

It gets more important with age, too. Men tend to lose 3% to 5% of their muscle mass per decade after 30, so the training you do in your 40s and beyond counts double.⁴

Testosterone and weight loss

Healthy testosterone levels support the things that make weight loss easier: energy, motivation, and lean muscle, which burns more calories at rest than fat. If weight is part of the picture, our weight loss programme can help.

The numan take

Testosterone builds muscle, but it can't do it alone. Training, protein, sleep, and healthy hormone levels work together. Check where your testosterone stands, then put the work in. And if your levels turn out to be low, there's a clear path forward.

References

^{1 Griggs, R. C., Kingston, W., Jozefowicz, R. F., Herr, B. E., Forbes, G., & Halliday, D. (1989). Effect of testosterone on muscle mass and muscle protein synthesis. Journal of Applied Physiology, 66(1), 498–503. https://doi.org/10.1152/jappl.1989.66.1.498}

^{2 Tsujimura, A. (2013). The relationship between testosterone deficiency and men's health. The World Journal of Men's Health, 31(2), 126–135. https://doi.org/10.5534/wjmh.2013.31.2.126}

^{3 Saad, F., Aversa, A., Isidori, A. M., Zafalon, L., Zitzmann, M., & Gooren, L. (2011). Onset of effects of testosterone treatment and time span until maximum effects are achieved. European Journal of Endocrinology, 165(5), 675–685. https://doi.org/10.1530/EJE-11-0221}

^{4 Harvard Health Publishing. (2022). Building better muscle. Harvard Medical School. https://www.health.harvard.edu/staying-healthy/building-better-muscle}