Testosterone but not estradiol level is positively related to muscle strength and physical performance independent of muscle mass: a cross-sectional study in 1489 older men

Objective: To examine the relationship between different measures of testosterone and estradiol (E-2), muscle mass, muscle strength, and physical performance; and to test whether the association of sex hormone level with muscle strength and physical performance was independent of muscle mass. Design and methods: A cross-sectional survey on 1489 community-dwelling men older than 64 years of age. Serum levels of testosterone and E2 were measured by mass spectrometry, and sex hormone-binding globulin (SHBG) levels were measured by immunoradioassay. Muscle mass was examined by dual-energy X-ray absorptiometry and physical performance was assessed by hand-grip strength, gait speed, step length and chair-stand test. Results: Appendicular skeletal mass (ASM) was positively associated with total testosterone (TT; P<0.001), free testosterone (FT; P<0.001), and total E-2 (P<0.001) but not with free E-2 (P=0.102). After adjustment for age, serum SHBG and relative ASM, both TT and FT were significantly associated with grip strength, narrow-walk speed and the composite neuromuscular score. Higher total E-2, but not free E-2 was associated with lower grip strength (P<0.05) after adjustment for age, FT, SHBG and relative ASM. Conclusions: Testosterone level was related to both muscle mass, strength and physical performance. Total E-2 level, though related to muscle mass positively, affected muscle strength adversely in older men.