The Effects of Weight Training on Women

There's a phrase women still hear frequently in the fitness world:

"If I train with weights, I'll get very muscular."

It's no coincidence that elite sports have separate categories for men and women; biologically, men have a distinct advantage in strength, speed, and endurance thanks to their greater average muscle mass, higher hemoglobin levels, and larger bone structure. At the heart of this difference lies testosterone. A large summary study by Handelsman et al. (2018) shows that performance differences in adults can be largely explained by circulating testosterone levels .

This data also helps us understand that it is biologically highly improbable for a woman with normal hormone levels to "accidentally become muscular and look like a man" simply by weight training.

Female and Male Testosterone: The Numerical Facts

Handelsman 2018, using the reliable measurement method LC-MS to analyze large series, provides the following reference ranges:

• Healthy young men: 7.7 – 29.4 nmol/L

• Healthy premenopausal women: 0 – 1.7 nmol/L

Well:

• Men's testosterone levels are approximately 15–20 times higher than women's .

• The distributions hardly overlap : the testosterone range for "normal men" and "normal women" is distinctly separated.

• Even when mild hyperandrogenic conditions such as polycystic ovary syndrome (PCOS) are taken into account, a reasonable upper limit of 5 nmol/L is recommended for women; levels above this are generally considered to be associated with conditions such as tumors, DSD, doping, etc.

  
  

  

This means that a normal woman's hormone profile is structurally well below the range that would allow her to develop "male-type muscle mass." Weight training doesn't change this biological fact; it simply optimizes the body within this range .

Same Training, Different Results

Research has shown since ancient times that muscle strength is related to androgens (particularly testosterone and DHT). At the modern level, testosterone binds to androgen receptors in muscle cells, triggering a series of cellular responses:

• It increases the number and size of muscle fibers.

• It increases the number of satellite cells and myonuclei , which play a role in muscle repair .

• It increases the size of motor neurons.

• It also enhances muscle energy production and endurance through mitochondrial biogenesis , IGF-1 production , and myoglobin expression .

On average, women have 50–60% of men's upper body muscle mass and 65–70% of their leg muscle mass . Women's upper body strength is approximately 50–60% of men's , while their leg strength is 60–80% . Even at the same age and weight, men have an average of 12 kg more muscle mass . This difference is explained not only by genetics or athletic history, but also by differences in circulating testosterone levels .

The article presents a clear picture when age group performance data and testosterone levels are overlaid:

• Girls and boys perform similarly during the pre-puberty period.

• In boys, testosterone levels rise rapidly with puberty; in girls, however, they remain in the <2 nmol/L range.

• After this period, men experience greater muscle development than women.

  

The study concludes:

Much of the difference in gender performance in adult sports can be explained by the effects of circulating testosterone on muscle mass, muscle strength, bone size, and hemoglobin.

This difference arises not because "men work out," but because men's testosterone levels are many times higher than women's . Therefore, a woman with normal hormone levels is not expected to reach male-level muscle and performance through training alone.

What do these statistics tell us about women's weight training?

Handelsman's compilation focuses primarily on elite sports, category fairness, and testosterone levels; however, the physiology he reveals offers important lessons for everyday life.

• A woman's testosterone level within the normal range is at the "lower plateau" end of the testosterone dose-response curve on muscle function.

• Dramatic effects on muscle, bone, and hemoglobin only become apparent when testosterone levels rise above the female physiological range , i.e., into the male range (e.g., ≥5–7 nmol/L and above).

  
  

What does this mean?

• A woman with natural hormone levels:

  • It gets stronger when you lift weights .

  • Muscle tissue increases somewhat, the body looks firmer,

  • However, since testosterone levels do not reach the male range, there is no biological basis for excessive hypertrophy resembling a "male body."

    
    

  "Accidentally becoming very muscular" is not a scenario consistent with this physiology. On the contrary, even elite-level muscle development requires years of high-volume training, good nutrition, and genetic advantage for women.

So why should women do weight training?

Weight training has many health benefits for muscle and bone health, mental health, cardiovascular health, metabolism, and posture, but that's a topic for another article. Since this article specifically focuses on women's weight training, we won't stray from the subject.

Most women want to "look thinner, firmer, and fitter." Ironically, it's not cardio that achieves this look, but muscle mass. Fat loss without muscle mass often results in a "thin but shapeless" body. Resistance training increases muscle tone, reduces body fat, and makes the body firmer, more defined, and balanced . Furthermore, weight training allows you to target specific muscle groups, isolating and developing areas where you want to increase strength or mass.

Moreover, muscle is a metabolically active tissue; meaning it expends energy even when at rest. This translates to a faster metabolism, easier weight control, and longer-term fat loss. In short, women should do weight training to look fit , not to "build muscle . "

Weight training unlocks the potential of the female body in the most natural and safe way. Muscle doesn't "harden" the body — it defines, balances, and refines it. Cardio might make you smaller, but weight training shapes you.

So the point isn't "getting too muscular," but rather using your muscles to design your own body. Because beauty doesn't contradict strength — strength is the most enduring form of beauty.

Reference:

• Handelsman DJ, Hirschberg AL, Bermon S. Circulating Testosterone as the Hormonal Basis of Sex Differences in Athletic Performance. Endocr Rev. 2018 Oct 1;39(5):803-829. doi: 10.1210/er.2018-00020. PMID: 30010735; PMCID: PMC6391653.