Muscle function in monozygotic female twin pairs discordant for hormone replacement therapy

Introduction: Postmenopausal monozygotic twin pairs discordant for hormone replacement therapy (HRT) provide an advantageous study design controlling for genetic background for elucidating the relationships between aging, sex hormone levels, muscle strength, contractile capacity, and fatigability. Methods: Thirteen postmenopausal monozygotic twin pairs discordant for HRT were measured for maximal voluntary torque (MVC) and twitch characteristics using electrical stimulation before and after intermittent dynamic plantarflexor exercise until exhaustion. Results: Peak twitch torque was 32% higher in HRT users than in their non-HRT, genetically identical sisters (P = 0.002), but MVC did not dif…