Muscular strength and power are correlated with motor unit action potential amplitudes,but not myosin heavy chain isoforms in sedentary males and females |
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| Institution: | 1. Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia;2. Department of Biomedical Engineering, Faculty of Engineering and Technology, University of Ilorin, P. M. B. 1515 Ilorin, Nigeria;3. Department of Rehabilitation Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur 50603, Malaysia;4. Clinical Exercise and Rehabilitation Unit, Discipline of Exercise and Sports Sciences, Faculty of Health Sciences, The University of Sydney, Sydney, 2006 NSW, Australia;1. Graduate School of Health and Sports Science, Juntendo University, Chiba, Japan;2. The Leonard Davis School of Gerontology, University of Southern California, California, USA;3. Faculty of Medicine, Tokai University, Kanagawa, Japan;4. Faculty of Nursing and Nutrition, University of Nagasaki, Nagasaki, Japan;5. Faculty of Education, University of Miyazaki, Miyazaki, Japan;6. Faculty of Liberal Arts, The Open University of Japan, Chiba, Japan;7. Faculty of Management and Information Sciences, Josai International University, Chiba, Japan;8. Faculty of Pharmacy, Meijo University, Aichi, Japan;9. Faculty of Sport and Health Science, Ritsumeikan University, Shiga, Japan;10. Faculty of Sport Sciences, Waseda University, Saitama, Japan;11. Faculty of Health and Nutrition, Tokyo Seiei College, Tokyo, Japan;12. Department of General Medicine, Mito Medical Center, Tsukuba University Hospital, Ibaraki, Japan |
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| Abstract: | It remains unclear if the sizes of higher-threshold motor units (MU) are associated with muscular strength and power. Therefore, the purpose of this study was to examine sex-related differences in muscle cross-sectional area (mCSA), percent myosin heavy chain (%MHC) isoform expression, and the MU action potential amplitudes (MUAPAMPS)-recruitment threshold (RT) relationships of the vastus lateralis and isometric peak torque, isokinetic peak torque and mean power at 1.05 rad·s−1 of the leg extensors. Surface electromyographic decomposition techniques were used to quantify MUAPAMPS recorded during isometric muscle actions at 70% of maximal voluntary contractions and regressed against RTs with the slopes calculated. Ultrasound images were used to measure mCSA. Males had greater slopes from the MUAPAMP-RT relationship than the females (P < 0.05). The greater slopes likely reflected larger higher-threshold MUs for the males. The mCSAs and slopes from the relationships were strongly correlated with isometric and isokinetic peak torque and isokinetic mean power (r = 0.78–0.82), however, type I %MHC isoform was only moderately correlated with isometric peak torque (r = −0.54). The results indicated that sex-related differences in muscular strength and power were associated more so with the sizes of the higher-threshold MUs (slopes) and mCSA than MHC isoforms. The amount of cross-bridge activity within muscle fibers that comprise higher-threshold MUs may be the primary contributor to muscular strength and power rather than the contractile properties of the muscle. |
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| Keywords: | Motor unit action potential amplitude Muscle cross-sectional area Isokinetic Myosin heavy chain Ultrasound EMG decomposition |
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