Testosterone is the primary male sex hormone and is responsible for the development of masculine features during puberty, including a rapid increase in muscle growth. It is produced primarily in the testes, but also small amounts of this powerful steroid hormone are produced in the adrenal glands, located on top of the kidneys, and in females it is also produced in lesser amounts in the ovaries.
Although often associated with androgenic male sexual characteristics such as increased body hair, muscle mass and a deeper voice, testosterone production in women is also important for general health and well-being, however the lower amounts women typically produced is a fundamental reason as to why women do not typically carry as much muscle as men, and is one of the reasons why women should not fear getting too bulky when lifting weights. Developing muscle tissue is hard enough for most men and they have much, much greater levels of this potent muscle building hormone, so in general women need not be worried. That being said, lifting weights can cause acute elevations in women’s testosterone levels and this is a positive thing for fat loss, health, maintaining metabolism, preserving lean tissue when dieting and long term bone health.
The steroid hormones (testosterone, oestrogen, progesterone etc.) are derived from cholesterol and links have been shown between low dietary fat intake and reduced levels of testosterone. As well as testosterone being beneficial for muscle growth, it also plays important roles in fatty acid metabolism and regulating body fat levels. Testosterone can help with the breakdown of body fat for use as a fuel, however it can also be converted to oestrogen through a process called aromatisation under the influence of an enzyme found in fat tissue called aromatase. It is this process that means overweight men can develop a reduced sex drive and ‘man boobs’ if body fat levels become too high. Testosterone also plays an important role in maintaining bone health and this too can be put at risk in the obese. It is also a reason why women, when their natural levels of oestrogen start to fall, are at risk of developing bone disorders as their steroid hormones are in decline after menopause, whereas men produce testosterone their entire life.
Testosterone generates its actions in a similar manner to thyroid hormone (see part 2 in this series). Being fat soluble, it can pass through cell membranes and directly target receptors in the nucleus. This then causes our genes, which are codes to produce proteins, to combine amino acids in a specific order to produce the cell specific proteins that testosterone instructs it to. In a muscle cell this would be new muscle proteins, and this is how testosterone stimulates protein synthesis in order to generate muscle growth.
Testosterone also has unique interactions with other hormones, most notably growth hormone and our ‘stress hormone’ cortisol. Testosterone has the potential to stimulate the release of insulin like growth factor-1 (IGF-1) which has mild anabolic effects, but a positive effect on preventing muscle protein breakdown adding to the amount of muscle we can potentially grow. Cortisol gets a bad reputation as it is associated with catabolic processes including the breakdown of muscle protein and is associated with many health conditions if elevated chronically. However, we will discover later on in our series (Part 6) that maybe it’s not quite as bad as many make it out to be. Cortisol is acutely elevated during resistance training which has positive effects on muscle breakdown, which we need to remodel and grow new tissue.
The real issue is if we get chronically high levels of cortisol, and this is especially problematic when combined with low testosterone. If we have a high cortisol to testosterone ratio, this can mean that we are creating more tissue breakdown (catabolism) than we are building tissue (anabolism) and this is obviously not a good thing for the body! Key factors that can generate an unwanted testosterone to cortisol level include prolonged periods of severe calorie restriction, persistent environmental stress including lack of sleep, and these are all amplified when combined with overtraining. If this doesn’t sound like a recipe to explain the muscle loss and non-existent libido experienced by many bodybuilders in the latter stages of a pre-contest diet, then I don’t know what does!
In order to combat this, we can ensure that we do not place the body on severe calorie restriction, ensure an adequate amount of dietary fat, allow the body rest when feeling run down and the inclusion of carbohydrates at least periodically in large amounts, which will increase insulin; which has an inverse relationship with cortisol and, in short, when insulin goes up, cortisol goes down and at times, this is exactly what you’ll need.
Testosterone can also have a positive effect on structures and activity at the neuromuscular junction. This junction is the point where our nerves (motor neurons) meet the muscles. At the end ‘bulb’ of a motor neuron under stimulation by nerve impulses, this causes the release of neurotransmitters which are signallers for a muscle to contract. This enhancement in neuromuscular efficiency at the ‘junction’ is a key determinant in the strength gains associated with elevations in testosterone levels, independent of increases in muscle size.
It has been suggested that acute elevations in testosterone noted during resistance training are partly responsible for muscle growth, although it is still widely debated as to the extent these acute elevations in testosterone might have on long term muscle growth. It is also possible that a whole host of different factors are responsible for generating hypertrophy synergistically and that isolating any one of these outcomes in short term studies is unlikely to determine its true effect on hypertrophy. High volume, moderate to high intensity, short rest times and stressing large portions of muscle mass produces the highest hormonal elevations of testosterone, and this is similar to the findings that I described for GH in our previous article (check out Part 3: Growth Hormone).
In summary, in order to support testosterones’ effect on increasing muscle protein synthesis and muscle growth, it is important to provide enough fuel in the form of fats and carbohydrate combined with quality sources of protein to provide the amino acids to support this process. Enough dietary fat is essential to provide the raw materials for testosterone production and this should be combined with adequate calorie intake. The periodic use of a higher calorie refeed day, or even days, combined with adequate rest, may not increase testosterone levels significantly, but they may at least be able to reduce the impact of catabolic hormones working in opposition to testosterone.