Acute changes in motor unit discharge property after concentric versus eccentric contraction exercise in knee extensor |
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| Institution: | 1. Laboratory of Neuromuscular Biomechanics, School of Health and Sport Science, Chukyo University, 101 Tokodachi, Kaizu-cho, Toyota, Aichi 470-0393, Japan;2. Research Fellow of Japan Society for the Promotion of Science, Kojimachi, Chiyoda-ku, Tokyo 102-0083, Japan;3. Center for General Education, Aichi Institute of Technology, 1247 Yachigusa, Yakusa-cho, Toyota-shi, Aichi 470-0392, Japan;4. Faculty of Education and Integrated Arts and Sciences, Waseda University, 1-6-1, Nishiwaseda, Shinjuku-ku, Tokyo 169-8050, Japan;5. Faculty of Electrical Engineering and Computer Science, University of Maribor, Koro?ka cesta 46, SI-2000 Maribor, Slovenia;1. Faculty of Medicine, Memorial University of Newfoundland, St. John’s, NL, Canada;2. Division of Research and Innovation, Canadian Memorial Chiropractic College, Toronto, ON, Canada;1. Research Centre on Aging, CIUSSS de l’Estrie - CHUS, Sherbrooke, QC, Canada;2. Department of Mechanical Engineering, Université de Sherbrooke, Sherbrooke, QC, Canada;3. School of Rehabilitation, Université de Sherbrooke, Sherbrooke, QC, Canada;4. Department of Health Sciences, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada;5. Research Centre on Health, CIUSSS du Saguenay-Lac-Saint-Jean, Chicoutimi, QC, Canada;1. Department of Sports Medicine and Performance Physiology, Goethe University Frankfurt, Frankfurt, Germany;2. Department of Strength Power and Technical Sports, Institute for Applied Training Science, Leipzig, Germany;3. Department of Engineering and Industrial Design, Magdeburg-Stendal University of Applied Sciences, Magdeburg, Germany;4. Department of Biomechanics, Institute for Applied Training Science, Leipzig, Germany;5. Centre for Human Performance, School of Medical and Health Sciences, Edith Cowan University, Joondalup, WA, Australia;1. Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil;2. Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK;3. Department of Clinical and Experimental Sciences, Università degli Studi di Brescia, Brescia, Italy;4. Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Politecnico di Torino, Torino, TO, Italy;5. PolitoBIOMed Lab, Politecnico di Torino, Torino, Italy;1. Univ Lyon, UJM-Saint-Etienne, Laboratoire Interuniversitaire de Biologie de la Motricité, EA 7424, F-42023 Saint-Etienne, France;2. Université du Québec à Montréal (UQAM), Montréal, Canada;3. Unité de Myologie, Service de Physiologie Clinique et de l’Exercice, Centre Référent Maladies Neuromusculaires Euro-NmD, CHU de Saint-Etienne, France;4. Institut Universitaire de France (IUF), Paris, France;1. Faculty of Kinesiology & Physical Education, University of Toronto, Toronto, ON, Canada;2. Department of Kinesiology & Health Sciences, University of Waterloo, Waterloo, ON, Canada;3. Division of Research and Innovation, Canadian Memorial Chiropractic College, Toronto, ON, Canada |
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| Abstract: | This study aimed to investigate the motor unit firing property immediately after concentric or eccentric contraction exercise. Eighteen healthy men performed repetitive maximal isokinetic knee extension exercises with only concentric or eccentric contraction until they exerted less than 80% of the baseline strength. Before and after the fatiguing exercise, high-density surface electromyography of the vastus lateralis was recorded during submaximal ramp-up isometric contraction and individual motor units were identified. Only motor units that could be tracked before and after exercise were analyzed. Muscle cross-sectional area of the vastus lateralis was measured using ultrasound, and electrically evoked torque was recorded before and after the exercise. Sixty-five and fifty-three motor units were analyzed before and after the concentric and eccentric contractions, respectively. The results showed that motor units with moderate to high recruitment thresholds significantly decreased recruitment thresholds under both conditions, and the motor unit discharge rates significantly increased after concentric contraction compared to eccentric contraction. A greater muscle cross-sectional area was observed with concentric contraction. The evoked torque was significantly decreased under both conditions, but no difference between the conditions. These results suggest that fatiguing exercise with concentric contraction contributes to greater neural input to muscles and metabolic responses than eccentric contraction. |
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| Keywords: | High-density surface electromyography Motor unit discharge rate Fatigue Contraction mode Muscle swelling |
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