The effects of testosterone administration on muscle areas of the trunk and pelvic floor in hysterectomized women with low testosterone levels: proof-of-concept study.

The aim of this study was to determine the effect of testosterone administration on trunk and pelvic floor muscle area in women with low testosterone levels. Participants were hysterectomized women with total testosterone<31 ng/dL and/or free testosterone<3.5 pg/mL; participating in the Testosterone Dose Response in Surgically Menopausal Women (TDSM) trial. All participants received a standardized transdermal estradiol regimen during the 12-week run-in period, and were then randomized to receive weekly intramuscular injections of placebo, or 3, 6.25, 12.5, or 25 mg testosterone enanthate for 24 weeks. Muscle areas of the trunk and pelvis were measured at baseline and end of treatment using 1.5 Tesla magnetic resonance imaging. Total and free testosterone levels were measured by liquid chromatography-tandem mass spectrometry and equilibrium dialysis, respectively. Testosterone effect on muscle areas was analyzed using linear regression models. A total of 24 women who had available baseline and posttreatment magnetic resonance imaging were included in the analysis. Increased cross-sectional areas of the paraspinal, psoas, and abdominal wall muscles were seen after testosterone administration. The estimated mean change (95% CI; P value) between treatment groups was 4.07 cm (1.26-6.88; P = 0.007) for paraspinal, 1.60 cm (0.10-3.09; P = 0.038) for psoas major, and 7.49 cm (1.96-13.02; P = 0.011) for abdominal wall muscles. Increases in psoas muscle area were significantly associated with changes in free testosterone concentrations. No significant changes in obturator internus and pelvic floor muscle areas were observed. Short-term testosterone administration in women with low testosterone levels was associated with increased trunk muscle area.