When your testosterone levels drop significantly, you know about it. You feel distinctly different. Your quality of life takes a nosedive. You’ve been looking for your libido, but you can’t find it anywhere. Things you once looked forward to are now dull inconveniences. One day you’re cleaning the house. You find your libido. In the toilet. 💩

No one wants to put in a ton of effort and get nothing back. But if you’ve always had low testosterone, you might not know anything’s wrong until you find you’re struggling to build muscle.

If you’ve dialled in every training variable, but you’re still not making gains and are wondering what gives, maybe it’s time to test your testosterone. 🧪

In this article, I cover:

• What we actually mean by low testosterone.
• How higher or lower levels of testosterone can affect muscle growth.
• Whether or not you can build muscle with low testosterone.
• How much testosterone you need to see results.

What do we mean by low testosterone?

First, we need to define what we mean by ‘low’ testosterone.

You’ve probably heard about the concerning trend of declining testosterone levels over the last few generations. Anecdotally, official levels of ‘optimal’ or ‘normal’ testosterone appear to have dropped too. Presumably as a result of the new (lower) normal.

Optimal levels, then, are likely a little ways off the bottom of today’s ‘normal’ range, which a quick search online reveals to be 300-1,000ng/dL.

There’s a massive spread, though, between 300 and 1000ng/dL. At 300ng/dL, your levels are closer to zero than they are to the top of the range. But these ranges apply to total testosterone. And when it comes to physiological responses to the big T, it’s free testosterone you should be interested in.

Free vs total testosterone

Free, or ‘unbound’ testosterone circulates through the blood freely, and can latch onto receptor sites in body tissue (like muscle) to work its magic.

Other molecules circulate through your body - sex hormone binding globulin (SHBG), and albumin - and testosterone can bind to these instead. Testosterone that’s ‘bound’ like this can’t latch onto receptor sites, so it can’t ‘express’ itself, or affect you in the normal ways you’d expect.

So someone with higher total testosterone who also has higher levels of SHBG and other binding molecules, won’t experience the same effects.

On the other hand, those with lower total testosterone, but also fewer total binding molecules, could have higher free testosterone. As a result, they could exhibit more of the signs of high testosterone than our friend with high total test and high SHBG and albumin.

It’s worth mentioning - free testosterone is difficult to measure directly. What you see in blood tests tends to be an estimate based on your total testosterone and levels of SHBG.

But it’s still an important figure. So, if you’ve had a recent blood test and are concerned about a lower-than-expected level of total testosterone, take a quick check of your free test before jumping to any conclusions.

The symptoms of low testosterone

By now you should be getting a sense of the truth: ‘low testosterone’ isn’t a black and white, “you have it, or you don’t” phenomenon. Symptoms exist on a scale, and can crop up even when levels are apparently normal for a number of reasons - if SHBG climbs too high, for example.

Broadly speaking, if your total testosterone is below 400ng/dL, you might be experiencing some detrimental effects that could be improved by boosting those levels. It’s unlikely (though not impossible) that you’d have issues if your levels are above 500ng/dL.

If your levels are below 300 and you’re otherwise young and fit, then you’ve got something worth investigating.

Unfortunately, edge cases that don’t fit the mould often get left out and forgotten about. If you suspect something is wrong, and you’ve got the budget for it, then it’s worth looking into. And if your levels look normal, but you’re experiencing many of the below symptoms, there could be something else going on:

• Low libido.
• Erectile dysfunction.
• Hot flashes.
• Fatigue.
• Irritability.
• Slow hair growth or hair loss.

Testosterone and muscle growth

Alright, so that’s low testosterone in a nutshell. What’s testosterone’s relationship with muscle growth?

Spikes in testosterone after resistance training

You may have heard that lifting weights raises testosterone levels. While this is true, the change is ‘acute’, meaning it’s short-lived. Testosterone levels stay elevated for a short while after training, then return to baseline levels.

It’s thought this acute increase might have something to do with the body shifting protein balance in favour of muscle protein synthesis, which spurs muscle repair and growth. If this is true, then anything interfering with a proper boost in anabolic hormones, including testosterone, after training might limit how much muscle you can grow from the session.

But there are other ways chronically low testosterone might impact muscle growth.

Low testosterone and impaired FGF2 expression in muscle tissue

Ghanim et al. found that FGF2 expression in muscle tissue was 57% lower in men with hypogonadotropic hypogonadism than in those with normal testicular function⁽¹⁾. After 22 weeks of testosterone replacement therapy (TRT), FGF2 expression increased, while expression of myostatin and MRF4 decreased “significantly”.

Let’s break down the findings from that study:

First, the hypogonadal subjects had much lower expression of FGF2 in muscle tissue at the start of the study.

Second, after 23 weeks of TRT, FGF2 expression in skeletal muscle increased by as much as 179%, lifting it to similar levels as subjects with normal testicular function.

Third, plasma concentrations of IGF-1, another important regulator of muscle growth, also increased.

Fourth, myostatin, a protein that inhibits muscle growth, decreased in expression after 23 weeks of TRT.

So, this study showed that very low levels of testosterone wreak havoc on some of the mechanisms that govern muscle repair and growth. Those being FGF2, IGF-1, and myostatin expression in muscle tissue.

What the study does not show is how these mechanisms would respond to merely low testosterone levels in the region of 200-400ng/dL, and how those might differ from very high levels of testosterone above 800ng/dL.

Women and testosterone

The average woman has 10-20 times less testosterone than the average man - around 15-70ng/dL. Despite that, women can transform their physiques, adding respectable amounts of muscle mass, when they begin resistance training.

What’s important about this is it shows significant muscle growth is possible (relative to an untrained state) with low levels of circulating testosterone. The ceiling for that growth is lower, but growth can and does occur.

I’d argue this does a good job at filling the gap in our concerns with the study mentioned earlier. Namely, that it doesn’t show the consequences of merely low levels of testosterone in the region of 200-400ng/dL. This is still higher than the levels observed in women (15-70ng/dL), who are capable of building muscle through training.

Can you build muscle with low testosterone?

Given that women can build appreciable muscle mass from baseline with less than 100ng/dL of testosterone, I think it’s safe to say you, too, can build muscle by resistance training. Even with low testosterone.

But there are other factors that will impact the amount of muscle you’ll be able to build.

These include your:

• Training age.
• Genetics.
• Training stimulus.
• Other training variables.

Training age

Your ‘training age’ is the amount of time you’ve been resistance training. When you’re a complete novice and have had no experience at all, your body is incredibly receptive. Even with low testosterone, you’re likely to see results fast.

That said, your results won’t be as pronounced as they would be if your testosterone levels were normal or high.

Also, once you’re past the ‘newbie gains’ phase (roughly the first year of training), you’ll find your gains stalling much earlier than other trainees.

Genetics

Just as training novices are far more receptive to the stimulus resistance training provides, some people are more genetically predisposed to respond well, and respond quickly, than others.

If you’re a genetically gifted high responder, you’ll build more muscle than someone less genetically gifted, potentially even with the handicap of low testosterone.

Training stimulus

The way you set up your training is important, too. The more optimised your training is, the more gains you’ll be able to eke out.

Acute increases of hormones like testosterone after training seem to be inextricably tied to the muscle building process⁽²⁾. So you might be less receptive to any raw training stimulus when your testosterone is low. Plus, you’ll recover more slowly from any stimulus, giving you fewer opportunities to stimulate growth each month⁽³⁾.

Other training variables

Just as a highly optimised, individualised training routine will net you more gains than a bog standard one might be able to, the same goes for optimising other training variables.

That means your:

• Nutrition.
• Sleep.
• Supplementation.
• Stress.
• Active recovery.
• Other physical activity.
• Caloric intake.

If all these are on point, you’ll maximise your recovery capabilities. This might offset your otherwise impaired recovery slightly, increasing overall growth potential.

How much testosterone is needed to build muscle?

So how much testosterone do you need to build muscle? 🧐

Some muscle growth possible with T levels above zero

Since unenhanced women are able to build appreciable muscle mass, you’ll be able to build some muscle so long as your testosterone isn’t at zero.

But is it the case that, the more testosterone you have, the more muscle you’ll be able to build? 🤔

More test, more muscle?

When bodybuilders go enhanced for the first time, they’re able to gain incredible amounts of muscle mass. Even if they’d reached their natural genetic ceiling beforehand. This is true even if testosterone is all they take.

For that reason, I think it’s safe to assume that the more testosterone you have, the more muscle you’ll be able to build… as a general rule.

Other factors

But as we’ve spoken about before, there are all kinds of variables impacting muscle growth. If your testosterone levels are lower than the next guy’s but you’ve dialled in every training variable under your control and he hasn’t, you may well match or exceed his progress.

All this stuff matters. If you suspect you have low testosterone, get it checked. But don’t make a decision based on a single data point. Especially if there are other factors relating to your training and lifestyle you know you’re dropping the ball on.

How do I know if my testosterone levels are low?

Mail-order blood test services, like Thriva and Optimale in the UK, are accessible ways of testing your testosterone levels. These at-home testing kits are simple to use and deliver pretty accurate results.

But we’ll say it again: a single test gives you a single data point. With the many variables that affect your testosterone levels, you need to establish a clear trend of consistently low, or declining, testosterone over a period of months or years before you should be worried.

It’s best to test regularly and build a profile of multiple data points to establish a trend. This’ll give you a sense of what’s normal and how you respond to changes in your lifestyle, diet and training.

Also, bear in mind that some people are high responders. They’re genetically predisposed to respond like crazy to lower levels of circulating testosterone. If that’s you, you might consistently have levels sitting at around 400ng/dL, but feel fine and notice great progress in the gym.

Others might have twice that amount and be less sensitive to it, meaning they’ll see similar progress despite their higher concentrations.

TL;DR

Alright, so what does all this mean in practical terms?

First, if your testosterone levels are consistently below 400ng/dL over a period of months or years and you have symptoms of low T, speak to your doctor.

Second, if they’re within the normal range but you have strong symptoms over a period of months or years, speak to your doctor.

Third, for most people, a single low reading is nothing to worry about

Fourth, as a general rule, the more testosterone you have the more muscle you’ll be able to build. But raising your testosterone levels naturally is a multifaceted endeavour consisting of advice that boils down to, “eat well, exercise, and lose body fat”.

Fifth, most people will serve themselves best by optimising their training instead. If you’re not consistently getting stronger in the gym, troubleshoot your lack of progress by asking yourself the following questions:

• Am I training close enough to failure?
• Am I doing enough volume for my stalled body parts?
• Am I doing too much volume or work overall? Do I need a break from training?
• Do I need to rotate in new exercises for a novel stimulus?
• Am I getting a minimum of seven or eight hours of quality sleep every night?
• Am I definitely eating in a caloric surplus?
• Am I eating a gram of protein for every pound of my body weight?

To further troubleshoot stalled progress, check out our guide to the fundamental principles of muscle building.

References

1. Ghanim, Husam et al. “Effect of Testosterone on FGF2, MRF4, and Myostatin in Hypogonadotropic Hypogonadism: Relevance to Muscle Growth.” The Journal of clinical endocrinology and metabolism vol. 104,6 (2019): 2094-2102. doi:10.1210/jc.2018-01832. PMID: 30629183.
2. Kraemer, William J et al. “Growth Hormone(s), Testosterone, Insulin-Like Growth Factors, and Cortisol: Roles and Integration for Cellular Development and Growth With Exercise.” Frontiers in endocrinology vol. 11 33. 25 Feb. 2020, doi:10.3389/fendo.2020.00033. PMID: 32158429.
3. Kraemer, William J et al. “Recovery responses of testosterone, growth hormone, and IGF-1 after resistance exercise.” Journal of applied physiology (Bethesda, Md. : 1985) vol. 122,3 (2017): 549-558. doi:10.1152/japplphysiol.00599.2016. PMID: 27856715.