Background: Testosterone is crucial for muscle hypertrophy and strength. In transgender men on testosterone therapy, hormone levels reach the male range, yet previous studies show inconsistencies due to poor matching for physical activity and training experience. This study compared strength and hypertrophic responses between transgender men on stable testosterone therapy and cisgender men, matched for activity level and training history.

Methods: Twenty-six inactive men (13 cisgender, 13 transgender on testosterone ≥1 year) performed an 8‑week progressive resistance training program (leg press, 5 sets, 8‑12 reps, 60‑75% 1RM). Vastus lateralis and rectus femoris (upper/lower regions) thickness were measured by ultrasound, and strength by 1RM test. Data were analyzed by two‑way repeated‑measures ANOVA.

Results: Both groups significantly improved all strength and hypertrophy variables (p<0.001). The group×time interaction for rectus femoris strength was not significant (p=0.215). However, a region‑specific hypertrophy effect was found: only the upper rectus femoris showed greater increase in transgender men versus cisgender men (p=0.039), with no differences in vastus lateralis or lower rectus femoris (p>0.05).

Conclusion: Resistance training improved strength and hypertrophy in both groups. Transgender men showed greater upper rectus femoris hypertrophy, possibly due to biomechanical differences, heterogeneous androgen receptor distribution, or testosterone‑dependent regional responses. These findings may inform personalized training, but generalization requires further research.