Testosterone and Lean Mass

Testosterone and Lean Mass

Written by Ben Bunting: BA, PGCert. (Sport & Exercise Nutrition) // British Army Physical Training Instructor // S&C Coach.

Testosterone concentrations correlate positively with fat-free mass, leg muscle size and strength in young males who are healthy.

Administration of exogenous testosterone for 20 weeks shifts weight loss towards greater reduction of fat mass while simultaneously maintaining or increasing lean mass gains and handgrip strength.

Testosterone therapy increases both fat-free mass and muscle size in men with low testosterone levels, due to inhibiting fat cell differentiation and aromatisation of testosterone to estradiol. This occurs through inhibition of cell differentiation as well as aromatisation to estradiol.

Testosterone and Lean Mass

Testosterone is an androgen that plays an essential role in skeletal muscle growth and maintenance, especially among males.

Though testosterone concentrations in premenopausal females tend to be much lower compared to that in men, pre-menopausal females show similar muscle gains from resistance training as males.

Although low levels of testosterone exist within female bodies at low concentrations for reproductive and nervous system regulation purposes; its precise role regulating premenopausal women remains poorly understood.

Untrained young healthy men exhibit a strong positive correlation between testosterone concentrations and leg muscle size and strength when expressed as a percentage of body mass.

Hysterrectomized men experience similar correlations during menopause transition when testosterone circulating levels decline by approximately 50 percent.

However, little information exists on the relationship between endogenous testosterone, fat-free mass (FFM), and handgrip strength among premenopausal females.

With respect to secondary data from the National Health and Nutrition Examination Surveys used as sources, multiple linear regression was employed to analyze relationships among endogenous testosterone, free androgen index (FAI), SHBG lean mass and handgrip strength for 18-40 year old pre-menopausal women.

FFM changes were found to be positively correlated with testosterone changes (p 0.05), with an upward slope in FFM for every 100 ng/dL increase in testosterone outside of female physiological limits (13-56 ng/dL).

When adjusted for insulin, PCOS patients have higher insulin levels which decrease SHBG production. These results were unaltered even after making adjustments for insulin in this model.


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Testosterone and Fat Mass

Testosterone stimulates myogenesis and increases protein synthesis through its interactions with muscle-cell-expressed androgen receptors (AR), encouraging myogenesis and increasing protein synthesis.

Furthermore, testosterone also prevents protein degradation while encouraging satellite cells to differentiate into progenitor cells that differentiate into skeletal muscle fibers.

Finally, testosterone also increases fat oxidation while decreasing carbohydrate utilization, contributing to weight loss during periods of intense exercise.

Recently, in a randomised placebo-controlled trial involving obese dieting men with BMIs of 30 kg/m-2 who were randomly assigned either 56 weeks of intramuscular testosterone undecanoate or placebo was performed.

Results showed that fat loss was significantly greater among participants in the testosterone group than placebo, due to decreased abdominal fat as measured by dual energy X-ray absorptiometry and computed tomography.

Men participating in a randomized clinical trial (RCT) testing testosterone and participating in a 10-week very low energy diet (VLED) showed greater reductions of body fat than those receiving placebo and not participating in the VLED.

Men assigned testosterone and VLED also experienced an increase in lower-body lean mass index, reduced visceral fat mass accumulation and saw their bench press and squatting exercise strength improve significantly.

Another RCT investigated the relationship between endogenous serum testosterone levels and body composition using cross-sectional data from the National Health and Nutrition Examination Surveys.

Unadjusted and adjusted models demonstrated that total and free androgen index (FAI) positively associated with upper-body and lower-body muscle mass as well as handgrip strength.

On the contrary, total and truncal fat mass negatively associated with FAI.

Observational studies have also demonstrated the relationship between testosterone and body fat mass.

A longitudinal study in postmenopausal women demonstrated this correlation, with higher testosterone levels associated with decreased truncal fat and an increase in lean mass, while lower levels were linked with more abdominal fat and decreased lean mass.

This correlation can be explained through interactions between testosterone and estrogen which affect fat distribution, muscle mass development and overall body weight.

When conducted under an intention-to-treat approach for data missing value imputation, statistically significant dose response relationships between physiologic testosterone levels and both lower body and thigh muscle mass was discovered.

Testosterone also was associated with improved body composition among those suffering from polycystic Ovary Syndrome while showing negative correlations with BMI and truncal fat mass in those without PCOS.

Testosterone and Muscle Strength

Testosterone plays a significant role in maintaining muscle mass and strength for good physical functioning, which is necessary for good physical performance.

Testosterone also stimulates cellular signaling pathways that promote protein synthesis in muscle cells while inhibiting degradation, contributing to muscular growth.

Together with other factors, this makes testosterone an extremely potent performance enhancer.

Research indicates that men with low testosterone levels who undergo treatment experience increases in both size and strength gains.

Researchers conducted one study where they administered testosterone to healthy non-diabetic male subjects who were at risk of sarcopenia.

Participants received either placebo or 100 mg/d of testosterone daily for six months and were instructed to participate in weight training three times weekly comprising both bench press and squat exercises.

Subjects who received testosterone experienced greater gains in triceps and quadriceps muscles than their placebo-treated peers as well as increased shoulder and hip-flexion strength, and scored higher on 10-repetition maximal strength tests than their counterparts in placebo group.

These findings support the notion that low testosterone levels may contribute to sarcopenia and replacement therapy may reverse it.

However, due to being cross-sectional this study limits any inferences drawn from its data.

Furthermore, NHANES does not contain measures of growth hormone or IGF-1 which could potentially impact lean mass and strength.

Therefore, the authors of this study included these as covariates in their statistical model to try and account for any curvilinear relationships that might exist between testosterone, FAI and SHBG and handgrip strength or lean mass and handgrip strength respectively.

The authors found that their model with SHBG as a covariate explained a substantial portion of FAI-lean mass association, while including session of examination (morning, afternoon or evening) to account for diurnal variation in serum hormone concentrations and SHBG concentration.

They discovered these variables explained a large percentage of variance in FAI relationships with both lean mass and handgrip.

Testosterone and Performance

Testosterone impacts many body systems that contribute to physical performance, including muscle, fat, and bone density.

Furthermore, testosterone can alter an individual's response to startling stimuli as well as their empathy with others and motivation and confidence levels - factors that play an essential role in sports and other competitive activities.

Researchers examined the effects of testosterone on technical and physical performances among semi-professional soccer players.

They found an inverse relationship between postgame testosterone concentrations and ability to participate with the ball during games, and serum 25(OH)D levels and testosterone.

A significant correlation was also discovered between serum 25(OH)D levels and testosterone in this same group of subjects.

No such relationship between baseline testosterone concentrations and participation occurred, possibly suggesting vitamin D deficiency plays an integral part in how testosterone impacts athletic performance.

Studies on testosterone's impact on performance are somewhat conflicting. While some show that supplementing with testosterone increases nitrogen retention and fat-free mass in castrated animals and hypogonadal men.

Other research indicates that supraphysiologic doses do not enhance muscle strength in healthy adults.

Studies involving testosterone's effects on performance often employ non-standardized diets and exercise regimes or fail to account for caloric intake.

Other factors that could potentially have an effect include age, body mass index (BMI), genetic predisposition or social context.

A 2017 review of literature concluded that "there is no single, linear path that leads from T to increased athleticism."

For example, its authors point out a study conducted by track and field's global governing body and published in the British Journal of Sports Medicine found that increasing testosterone resulted in faster times during competition.

However, this also reduced endurance and power levels. Another Harper study conducted with eight amateur trans women runners comparing post-transition race times vs pre-transition race times revealed no improvements due to suppressing testosterone.


Research suggests a positive relationship between testosterone and lean mass.

Biologically active testosterone enhances fat-free mass through androgen receptor signalling in mature adipocytes, lipolysis promotion, anabolic pathways activation in myocytes (muscle fibre size and strength increasers), as well as supraphysiologic doses combined with resistance training enhancing muscle mass and strength gains in normal men.

Testosterone sends chemical messages that boost protein synthesis in muscle tissue, helping build more muscles.

But low testosterone levels prevent your body from receiving those muscle-building signals and instead cause muscles to convert to fat instead. Optimizing hormone levels helps preserve muscle mass while increasing strength.

Studies have demonstrated that when testosterone binds to receptors on muscle cells, it stimulates protein synthesis and increases muscle fiber size - leading to greater strength and endurance, making workouts and exercise routines simpler as well as helping control weight and increase energy.

Researchers discovered that men with low testosterone levels could still increase muscle growth by taking testosterone supplement pills in combination with resistance training and light exercise.

When comparing these two groups, those using both methods showed superior muscle development than their counterparts who only did light exercises or didn't take supplements at all - men who combined weight training and taking testosterone had greater gains than all the others groups combined.

Testosterone treatment was found to prevent lean mass loss during short-term, severe energy deficit in non-obese young men without obesity, significantly augmenting diet-induced decreases in both total and visceral fat mass reduction.

As opposed to placebo treatment which caused both muscle and fat mass reduction simultaneously, testosterone treatment resulted in nearly exclusive fat mass reduction instead.

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