Muscle function in monozygotic female twin pairs discordant for hormone replacement therapy |
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Authors: | Finni Taija Noorkoiv Marika Pöllänen Eija Ronkainen Paula H A Alén Markku Kaprio Jaakko Kovanen Vuokko Sipilä Sarianna |
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Institution: | 1. Neuromuscular Research Center, Department of Biology of Physical Activity, P.O. Box 35 (VIV227), University of Jyv?skyl?, FI‐40014 Jyv?skyl?, Finland;2. Gerontology Research Center, Department of Health Sciences, University of Jyv?skyl?, Jyv?skyl?, Finland;3. Department of Medical Rehabilitation, Oulu University Hospital, Oulu, Finland;4. Department of Public Health and Institute for Molecular Medicine, University of Helsinki, Helsinki, Finland |
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Abstract: | 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 differ. There were no differences in the activation level or twitch time characteristics between the co‐twins. Fatigue caused decreases in MVC (P = 0.001), twitch torque (P = 0.001), time to peak (P = 0.013), and half‐relaxation time (P = 0.001) similarly in HRT users and non–HRT users. Conclusion: In early postmenopausal women, involuntary but not voluntary force‐generating mechanisms of the plantarflexors are augmented by the use of HRT. Muscle Nerve, 2011 |
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Keywords: | aging estradiol fatigue plantarflexor strength skeletal muscle twitch |
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