Endocrine Abstracts

Background: The effects of gender-affirming hormonal therapy (GAHT) on body composition in transgender people assigned female at birth (AFAB) have been an area of interest. However, the impact of GAHT on muscle strength remains inadequately studied. We aimed to evaluate early alterations in muscle strength following GAHT in transgender people AFAB by isokinetic dynamometry, the gold standard for assessment of strength.

Subjects and Methods: A total of 20 transgender people AFAB were assessed at baseline, and after 3 months of testosterone injections. Fifteen participants were also assessed after 6 months. Muscle strength parameters including lower limb peak torque (PT), PT to body weight ratio (PT/BW) and average PT (AvPT) were measured using isokinetic dynamometry. Hand-grip strength (HGS) was also assessed by a dynamometer. Bioelectrical impedance analysis was used to assess body composition characteristics. Serum androgens, fasting glucose and insulin were measured at all three time points.

Results: The mean age and BMI (±SD) were 23.0±3.5 years and 25.1±5.7 kg/m² at baseline. Free androgen index was correlated with lean body mass (r=0.45, P=0.04), and fasting insulin was with truncal fat mass (r=0.65, P= 0.002) before initiation of GAHT. BMI did not show a significant change after 3 and 6 months of GAHT. After three months, significant increases occurred in knee flexors’ PT (56.6±18.7 N-m to 63.7±20.1 N-m, P=0.008), PT/BW (82.5±24.2% to 92.8±27.3%, P=0.01) and AvPT (52.1±17.0 N-m to 57.9±18.7 N-m, P=0.02), as well as in lean body mass (49.8±9.0 kg to 54.6±8.9 kg, P=0.001). There were no further alterations in these composition and strength parameters after 6 months. However, an increase in HGS was only significant after 6 months. Serum creatinine increased significantly with GAHT but remained within the normal range. Lean body mass and knee flexors’ AvPT were positively correlated at all timepoints. Muscle strength did not show any correlation with biochemical parameters including serum androgens and insulin.

Conclusion: Our results suggest an early increase in lower limb muscle strength and lean body mass within the first three months of GAHT in transgender individuals AFAB which are preserved and accompanied by a significant increase in upper limb strength at 6 months. Muscle strength appears to be associated with lean body mass. Given these outcomes, early initiation of an exercise plan to further enhance muscle mass and mechanical function may be considered for individuals undergoing GAHT.