Testosterone & Muscle: A Complicated Relationship

This article is from the Lifestyle section of our Library.

It's revered as the ultimate muscle-building hormone, “vitamin T”, but misunderstood about what can be realistically achieved naturally. 

Spend enough time in the gym, on fitness blogs or around athletes, and you'll hear about “boosting T levels” through supplements, specific foods, or different types of training. But what actually affects testosterone? Or does it even matter if it does?

The relationship between testosterone and muscle growth is undeniable. However, the difference between naturally increasing your testosterone levels and pharmaceutical increasing it is vastly different — far more than most people realise. 

Understanding this distinction is crucial for setting realistic expectations and making informed decisions about your goals.

This article examines what testosterone actually does in the body, how it influences muscle growth, the natural decline that occurs with ageing, and evidence-based strategies to support optimal testosterone production. 

You can read our comprehensive Muscle Growth Guide if you want to know about 26 other things that influence muscle growth (including testosterone).

Testosterone & Muscle: A Primer

The Master Regulator of Muscle?

Testosterone is a steroid hormone produced primarily in the testes (specifically in specialised cells called Leydig cells) in males, and to a much lesser extent in the adrenal glands and ovaries in females. 

In men, approximately 95% of testosterone production is controlled by “luteinizing hormone”, which is released from the pituitary gland in the brain.

While testosterone is known for regulating male sexual characteristics and reproduction, its role in muscle growth is equally effective. Testosterone functions as a master regulator of muscle mass and muscle growth.

It controls the rate at which your body synthesises new proteins — the fundamental building blocks of muscle. 

This process, called “muscle protein synthesis”, determines whether your muscles grow, maintain their size, or shrink. Higher testosterone levels accelerate this process, creating a more favourable environment for growth.

This increases muscle fibre size (or muscle “hypertrophy”), the enlargement of existing muscle cells, by increasing the protein content within each “fibre” — making the individual muscle fibres larger and stronger.

The Evidence?

The muscle-building effects of testosterone aren't theoretical; they're demonstrated clearly and consistently in controlled research. 

Many studies have shown that administering testosterone as a pharmaceutical drug substantially increases muscle growth, whether combined with exercise or not.

A landmark study in the New England Journal of Medicine divided men into four groups: no exercise with placebo, no exercise with testosterone (600 mg of testosterone enanthate a week), exercise with placebo, and exercise with testosterone.

The men receiving testosterone without any exercise gained more muscle mass than men who exercised without testosterone. The group that combined testosterone with exercise gained the most muscle of all, about 6 kg in just 10 weeks.

Even in clinical settings where testosterone is used as replacement therapy (TRT) at relatively modest doses to restore levels to normal ranges, it still triggers measurable muscle growth. 

These findings confirm that testosterone in its pharmacological form powerfully stimulates muscle growth.

Testosterone Works in Concert With Other Hormones

Testosterone doesn't operate in isolation. It works together with other “anabolic” (muscle-building) hormones, including growth hormone and insulin-like growth factor-1 (IGF-1). 

These hormones have overlapping and complementary effects, amplifying each other's muscle-building ability. This creates a more powerful anabolic environment than any single hormone could achieve alone.

T-Levels: Natural vs. Pharmaceutical

Here's where expectations meet reality. The presence of natural testosterone in your body is fundamentally different from what occurs when testosterone is administered as a therapeutic or performance-enhancing drug.

When testosterone is injected or applied transdermally (through the skin), it creates sustained, very high levels of free testosterone in the bloodstream — often 600% or more above natural levels. 

These elevated concentrations remain consistently high throughout the day and night, providing continuous anabolic signalling to muscle tissue for hours or days.

In contrast, natural testosterone levels fluctuate throughout the day. Healthy men experience peak testosterone levels in the morning, with concentrations gradually declining throughout the day. 

These peaks last minutes to a few hours rather than days or weeks. Natural testosterone levels, even when optimised through lifestyle factors, remain within a relatively narrow range.

This distinction is critical: changes in natural testosterone levels within the normal physiological range do not appear to impact muscle growth anywhere near as much as pharmacological doses do, if they impact it measurably at all. 

Research comparing men with naturally higher versus naturally lower testosterone (both within normal ranges) shows small differences in muscle-growth capacity.

What does this mean for Natural Lifters?

Does this mean improving natural testosterone is pointless? Not at all. Maintaining healthy testosterone levels supports overall health, energy, mood, motivation, recovery capacity, and training performance. 

These factors indirectly support muscle growth by enabling consistent, high-quality training and proper recovery.

However, realistic expectations are essential. Natural testosterone “optimisation” won't replicate the dramatic muscle-building effects seen with pharmaceutical doses. 

The goal should be maintaining normal, healthy testosterone production, rather than expecting drug-like muscle gains from lifestyle changes alone.

What Happens to Testosterone As We Age?

Testosterone levels naturally decline with age. After age 30, testosterone decreases by approximately 1-2% annually. 

While this decline is unavoidable, its effects are far from negligible over time. A 50-year-old man may have 20-40% lower testosterone than he did at age 30.

Low testosterone is associated with multiple negative outcomes, including reduced muscle mass, decreased strength, slower recovery from training, reduced motivation and drive, increased fat accumulation (particularly abdominal and visceral fat), lower energy levels, and reduced bone density. 

All of these factors compromise muscle growth potential, health, and overall quality of life.
However, the rate and severity of decline vary considerably between individuals. 

Genetics plays a role, but certain lifestyle factors significantly influence testosterone production and may slow age-related declines.

The Importance of Maintaining Healthy Levels

The difference between low-normal and high-normal testosterone levels within the physiological range may not dramatically affect muscle building, but the difference between clinically low testosterone and normal levels certainly does.

Men with clinically low testosterone (hypogonadism) experience genuine impairments in muscle building, fat loss, recovery, and overall health. For these people, medical intervention through testosterone replacement therapy may be appropriate and beneficial.

Training and T-Levels

Resistance Training: The Most Effective Natural Stimulus

The good news is that weightlifting and resistance exercise are among the most effective natural stimulators of testosterone production. 

Resistance exercise can increase testosterone levels by approximately 30% for up to an hour following training sessions. 

While this increase is temporary, regular training creates chronic adaptations that may support overall testosterone production.

More importantly, regular resistance training enhances how your muscle cells respond to testosterone — a concept sometimes called “testosterone sensitivity”. 

Just as insulin sensitivity determines how effectively your cells respond to insulin, testosterone sensitivity influences how effectively muscle tissue responds to the testosterone that's present. 

Improved sensitivity may amplify testosterone's effects even without dramatically increasing hormone levels whatsoever.

Does Training Type Matter?

Research suggests certain types of training may improve testosterone response to training. Compound exercises that engage large muscle groups (squats, deadlifts, presses, rows) appear to produce larger acute testosterone increases compared to isolation exercises. 

Training with moderate-to-heavy loads (70-85% of one-repetition maximum) for moderate volume (3-5 sets of 6–12 repetitions) and with relatively short rest periods (60-90 seconds) tends to generate more robust hormonal responses.

However, these acute hormonal spikes during and after training are probably not the primary driver of long-term muscle growth. 

The mechanical tension, metabolic stress, and muscle damage from training likely matter more than the hormonal responses. The hormonal benefits should be viewed as a supporting factor rather than the main driver of growth.

Can you Train Too Much?

While training stimulates testosterone, overtraining does the opposite. Excessive training volume without adequate recovery, combined with insufficient nutrition, can suppress testosterone production and elevate “cortisol”.

Cortisol is a catabolic hormone that opposes some of testosterone's effects, creating a poor hormonal environment for muscle growth and recovery.

Warning signs of overtraining include persistent fatigue, declining performance, increased resting heart rate, sleep disturbances, reduced motivation, frequent illness, and extended recovery times. 

If you experience these symptoms, reducing training volume and prioritising recovery is essential.

Nutrition and T-Levels

Dietary Fat & Testosterone

A balanced diet generally supports normal testosterone production, but dietary fat plays a particularly important role. Testosterone is synthesised from cholesterol (a type of fat), making adequate fat intake essential for hormone production.

Research shows that very low-fat diets (below 15% of total calories) can reduce testosterone levels. Conversely, diets providing 20-35% of calories from fat support normal testosterone levels. 

Beyond this range, eating more fat doesn't appear to increase testosterone further — there's an adequate intake threshold rather than a direct dose-response relationship (i.e., more isn’t always better). Your body can make cholesterol if and when it needs it anyway.

The type of fat also matters. 

Focus on healthy fats, including monounsaturated fats from olive oil, avocados, and nuts; omega-3 fatty acids from fatty fish (salmon, mackerel, sardines), cod liver oil, and flaxseeds; and moderate amounts of saturated fat from eggs, dairy, and quality meat sources. 

Avoid trans fats and minimise oxidised fats from heavily processed foods, as these may have negative effects on overall health and hormone production.

Micronutrients & Testosterone

While fat is the primary nutritional regulator of testosterone, several micronutrients play supporting roles. Zinc, magnesium, and vitamin D have all been shown to support testosterone production in research studies.

However, an important caveat applies: these nutrients appear most effective at correcting deficiencies rather than raising testosterone above normal levels in people with adequate status. 

If you're deficient in zinc, supplementation can normalise testosterone. But if your zinc levels are already adequate, additional supplementation won't further increase testosterone.

Zinc is essential for testosterone production and is found in oysters, red meat, poultry, beans, nuts, and whole grains. Deficiency is relatively common, particularly in vegetarians and people with high training volumes (zinc is lost through sweat).

Magnesium supports hundreds of biochemical reactions, including those involved in testosterone synthesis. Sources include leafy greens, nuts, seeds, whole grains, and legumes.

Vitamin D functions more like a hormone than a traditional vitamin and influences testosterone production. Many people have low vitamin D levels, particularly those living in northern regions or spending limited time outdoors. 

Fatty fish, egg yolks, and fortified foods provide some dietary vitamin D, though sunlight exposure and supplementation are often necessary for optimal levels.

Energy, Carbohydrate & Testosterone

While overlooked, adequate total energy (calories) intake is needed for normal hormone production. Severe calorie restriction, particularly when combined with high training volumes, can suppress testosterone and the production of other anabolic hormones.

Carbohydrate intake, particularly around training sessions, supports training performance, recovery, and energy availability, all of which indirectly support normal testosterone production. 

Very low-carbohydrate diets combined with intense training may compromise hormone production in some individuals, though responses vary.

Try to avoid chronic energy deficits unless fat loss is your primary goal, and even then, moderate deficits (300-500 kcal below maintenance) are preferable to aggressive restriction for supporting hormone production.

Lifestyle and T-Levels

Sleep & Testosterone

Sleep may be the most important lifestyle factor for testosterone production. Studies show that sleeping fewer than six hours per night can reduce testosterone levels by approximately 15% after just one week. The suppression becomes more severe with chronic sleep deprivation.

Testosterone is primarily produced during sleep, particularly during REM (rapid eye movement) stages. Disrupted or insufficient sleep interferes with nighttime testosterone production. 

Aim for 7–9 hours of quality sleep nightly, with consistent sleep and wake times to support circadian rhythm regulation.

Practical strategies to improve sleep include maintaining a cool, dark bedroom environment; avoiding screens for 1–2 hours before bed; establishing a consistent bedtime routine; limiting caffeine after early afternoon; and managing stress through relaxation techniques.

Stress & Testosterone

Chronic psychological stress negatively affects testosterone by increasing cortisol and other glucocorticoid hormones that directly inhibit testosterone release and production. Stress will shift the body toward a catabolic (breakdown) state rather than an anabolic (building) state.

Effective stress management techniques include regular physical activity, meditation or mindfulness practices, adequate social connection and support, time in nature, engaging hobbies and leisure activities, and setting boundaries around work and obligations.

Body Fat & Testosterone

The amount of body fat you carry, particularly visceral fat (the fat surrounding internal organs in the abdomen), significantly influences testosterone levels. High levels of visceral fat lower testosterone through an enzyme called aromatase, which converts testosterone into estrogen.

This creates a vicious cycle: low testosterone promotes fat accumulation, which further lowers testosterone. So, maintaining healthy body composition, typically 10-20% body fat for men, helps preserve normal testosterone levels.

Losing fat and improving body composition through proper nutrition and training can help normalise testosterone levels in overweight or obese individuals. This represents one of the most effective natural interventions for restoring testosterone in men with excess body fat.

Setting (Realistic) Expectations!

Naturally increasing testosterone production, sensitivity and/or activity through training, nutrition, and lifestyle factors can support healthy hormone levels within normal physiological range. 

This supports overall health, energy, recovery, training capacity, muscle mass preservation, and quality of life — all of which indirectly benefit muscle building.

However, naturally improving testosterone levels will not replicate the dramatic muscle-building effects seen with pharmaceutical testosterone use. 

You should not expect rapid, dramatic muscle gains beyond what's possible through proper training and nutrition alone, or physique development comparable to drug-enhanced athletes.

Disclaimer: No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.