The best available evidence does not support the claim that muscle growth in women is impossible or negligible. The 2025 Bayesian meta-analysis found that absolute increases in muscle size slightly favoured males, but relative increases in muscle size were similar between the sexes, with the authors concluding that females have a similar potential to induce muscle hypertrophy as males, particularly when measured as percentage change from baseline. Type II muscle fibre hypertrophy was similar between sexes; Type I fibre hypertrophy slightly favoured males. Roberts, Nuckols and Krieger (2020) reached a broadly similar conclusion about relative adaptations to resistance training.

On mechanism, the evidence is more nuanced than the post suggests. Reviews note that baseline testosterone differences are considered responsible for larger baseline muscle size in males, and that this contributes to women having roughly 50 to 60 percent of male upper body strength and 60 to 70 percent of lower body strength at the group level. However, the experimental work on whether testosterone drives the training response found the opposite of what the post implies: in West et al. (2010), despite very different acute testosterone responses between conditions, muscle mass and strength gains were comparable. The 2024 Exercise and Sport Sciences Reviews primer summarises that acute exercise-induced elevations in endogenous anabolic hormones do not enhance hypertrophy or strength. So testosterone explains where women start, not whether they can grow muscle from training.

On the "toned versus bulky" framing, exercise physiology sources are consistent that "toning" is not a distinct physiological process. Visible definition results from having muscle plus lower body fat, which is the same muscle-building process the post says does not happen.