Age-Dependent Muscular Response to Testosterone-Based Gender-Affirming Therapy: Evidence From a 1-Year Observational...

Area of Science:

• Endocrinology
• Reproductive Health
• Transgender Health

Background:

• Understanding age-related responses to testosterone therapy is crucial for transgender and gender-diverse individuals assigned female at birth (TGD AFAB).
• Previous research has not fully elucidated how age influences muscle adaptation to gender-affirming hormone therapy (GAHT).

Purpose of the Study:

• To investigate 1-year changes in muscle strength and mass in TGD AFAB individuals undergoing testosterone therapy.
• To examine age-specific differences in the response to testosterone-based GAHT.

Main Methods:

• A prospective longitudinal observational study enrolled 107 TGD AFAB adults.
• Participants were stratified into age groups (20-24, 25-29, 30-34, ≥35 years) and assessed for handgrip strength and body composition (dual-energy X-ray absorptiometry) at baseline and 12 months.
• Linear mixed models and quantile regression analyzed within-group changes and age-related trends.

Main Results:

• Handgrip strength increased across all age groups, with the most significant gains observed in younger participants (25-29 and 20-24 years).
• Muscle mass (appendicular skeletal muscle mass index) showed modest increases in younger individuals and plateaued or declined from age 30 onwards.
• The 30-34 age group exhibited a decline in muscle mass, particularly noticeable at the 25th percentile.

Conclusions:

• The age at which individuals start testosterone therapy significantly affects muscle adaptation.
• Strength gains are more pronounced in early adulthood and diminish with advancing age.
• Findings can inform age-appropriate clinical counseling for TGD AFAB individuals initiating testosterone therapy.