Testosterone and Muscle: How Much is Enough?

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It is well accepted that testosterone helps in building a muscular physique and strength. If it weren’t, there might be less temptation for some people to abuse steroids. Leaving that contentious issue aside, various studies do link healthy testosterone levels with muscle mass, strength and performance. Let’s look in more detail at this relationship, and the situations in which boosting levels may be desirable.

  1. There is an association between testosterone levels and muscle mass, strength and performance. It appears to increase the net protein synthesis within muscle fibres.
  2. Both testosterone and muscle mass generally decline with age. 
  3. However, the most convincing evidence that increasing levels can help in building muscle comes from people who start with low levels. If your levels are healthy, increasing them further may not assist you in building muscle. 

Evidence for testosterone’s effect on muscle

While longitudinal and cross-sectional studies show an association, there are few well controlled, randomised interventional studies that have directly examined the impact of increasing testosterone levels on muscle building and athletic performance among healthy people. Furthermore, this is unlikely to change in the future. Ethical considerations make trials of supplements problematic, seeing as testosterone can have marked effects beyond the muscles. For example, excessively high levels places you at increased risk of a whole host of problems, including blot clots, heart disease, liver disease, insomnia and mood swings, enlarged prostates and testicular shrinkage. Furthermore, testosterone studies among elite sportspeople are infeasible due to doping issues.

However, hypogonadal men (those whose levels are below a standard clinical threshold) have offered a safe opportunity to study the cause-effect relationship. Supplementation in these cases has often been beneficial. Furthermore, supplementation has been seen to boost muscle strength, mass and performance in females too. 

This leaves us in a position where we can say boosting levels when they start low is often beneficial, but we don’t know if it is when they start normal. The response may also vary between individuals, for example, according to age. 

Testosterone, muscle and ageing

We do know that levels naturally decrease with age- in both men and women. It is said that ageing is associated with 1-2% annual reductions. This may go some way to explaining the muscle atrophy (loss) that is also commonly associated with ageing. A preferential loss of fast twitch fibres with age may also be related to drops in testosterone. 

It is not clear whether muscle mass progressively decreases along with testosterone levels, or- as one longitudinal study of middle-aged and elderly Japanese men- loss occurs once levels dip below a critical threshold.

As a side note, testosterone also has positive effects on sexual development, bone strength, the immune system, fat mass, creation of mitochondria and brain function. 

How does testosterone help build muscle?

Testosterone appears to increase the net protein synthesis within muscle fibres. For example, in a small study among 65-75 year old (healthy and hypogonadal) men, it was seen that twice-weekly testosterone injections plus resistance training increased net protein synthesis increased more than resistance training and placebo. Note that both protein synthesis and breakdown increased. This means, to obtain the net muscle gains, amino acids released from the protein breakdown were reused, less of these were lost and it was unnecessary for muscle fibres to import more from the bloodstream. i.e. muscle-building from resistance training becomes more efficient. 

The precise details of how it accomplishes this is not completely elucidated. There is no doubt a complex network of effects at the genetic, enzyme and signalling molecule levels. For example, mice studies have shown testosterone regulates genes involved in muscle development, contraction and metabolism, and increases the availability of glucose and amino acids for glycogen and protein synthesis. Such findings cannot be relied upon as a direct representation of what happens among humans, but do offer some possible insights. 

It is also thought that testosterone may improve the neural component of strength (remembering that motor nerves must fire optimally for maximum force output). For example, there is some evidence that it may enhance the production of neurotransmitters, help the activity of motor nerves to fluctuate less, and encourage larger/more powerful motor units (i.e. those involving fast twitch muscle fibres) to fire earlier.

What is the healthy range for testosterone levels?

Different authorities suggest slightly different ranges, but they are all in a ballpark figure of each other:

  • The American Urology association suggests below 300 nanograms/decilitre of blood- when accompanied by symptoms- indicates low total testosterone
  • The Mayo Clinic suggests total levels should be in the range of 240-950 ng/dL for males aged 19 and up, and 8-60 ng/dL for females. 
  • Coming from a slightly different angle, some researchers have suggested that older men whose total testosterone <231 ng/dL could benefit from testosterone replacement therapy 

The Verdict

Low testosterone levels are associated with reduced muscle mass and strength. Healthy levels seem to facilitate protein synthesis within muscle, and it’s unlikely further increases will offer additional advantages as far as muscle building goes- but there may be unwanted side effects. On the other hand, if they are low or starting a downward trend with advancing age, there are ways to boost and/or maintain them. Stay tuned for our next post, 7 natural ways to boost testosterone and build muscle.

Have you got a burning question about hormones or muscle health?

References

American Urological Association (2018). Evaluation and Management of Testosterone Deficiency (2018). Accessed at: https://www.auanet.org/guidelines/testosterone-deficiency-guideline

Basaria, S., Coviello, A.D.,  Travison, T.G. et al. (2010). Adverse Events Associated with Testosterone Administration. The New England Journal of Medicine. 363:109-122. DOI: 10.1056/NEJMoa1000485

Haren, M.T., Siddiqui, A.M., Armbrecht, H.J., et al. (2011), Testosterone modulates gene expression pathways regulating nutrient accumulation, glucose metabolism and protein turnover in mouse skeletal muscle. International Journal of Andrology, 34: 55-68. doi:10.1111/j.1365-2605.2010.01061.x

Mayo Clinic Laboratories. Test ID: TTFB (Testosterone, Total, Bioavailable, and Free, Serum): Clinical and Interpretative. Accessed at: https://www.mayocliniclabs.com/test-catalog/Clinical+and+Interpretive/83686. (Accessed 2020, August 5). 

Steinacker, J.M., Koubaa, D., Nielsen, H.B. et al. (2019). Statement of FISA Sports Medicine Commission: Biological Effects of Testosterone.  Dtsch Z Sportmed, 70: 83-84. DOI:10.5960/dzsm.2019.368

Yuki, A., Otsuka, R., Kozakai, R. et al. (2013). Relationship between Low Free Testosterone Levels and Loss of Muscle Mass. Sci Rep 3, 1818. https://doi.org/10.1038/srep01818.

One thought on “Testosterone and Muscle: How Much is Enough?

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    6 September, 2020 at 1:09 am
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    Terrific article

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