Age-related decreases in motor unit discharge rate and force control during isometric plantar flexion |
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| Authors: | J. Kallio K. Søgaard J. Avela P. Komi H. Selänne V. Linnamo |
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| Affiliation: | 1. School of Medical Imaging, Xuzhou Medical University, Xuzhou, China;2. Department of Mechanical Engineering, University of Utah, Salt Lake City, UT, USA;3. Department of Biomedical Imaging and Radiological Sciences, National Yang-Ming University, Taipei, Taiwan;1. Carrera de Kinesiología, Departamento de Ciencias de la Salud, Facultad de Medicina, Pontificia Universidad Católica, #7820436 Santiago, Chile;2. School of Sport, Exercise and Rehabilitation Sciences, Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), College of Life and Environmental Sciences, University of Birmingham, # Edgbaston, B15 2TT Birmingham, United Kingdom;3. Centro de Investigacion en Fisiologia del Ejercicio (CIFE), Universidad Mayor, Santiago, Chile;4. Laboratory of Biomechanics and Kinesiology, Hospital San José, #8380419 Santiago, Chile;5. Laboratory of Clinical Biomechanics, Department of Physical Therapy, Faculty of Medicine, Universidad de Chile, #8380453 Santiago, Chile;6. Laboratorio LIBFE, Escuela de Kinesiología, Universidad de los Andes, #7620086 Santiago, Chile;7. Kinesiología, Universidad de Santiago de Chile, #9170124 Santiago, Chile;8. Servicio de Tobillo y Pie, Instituto Traumatológico, #8340220 Santiago, Chile;9. Facultad de Medicina, Universidad de Chile, #8380419 Santiago, Chile;10. Laboratory of Neuromechanics, Universidade Federal do Pampa, Campus Uruguaiana, #97508000 Uruguaiana, Brazil;11. Centro de Salud Deportivo, Clinica Santa Maria, #8340518 Santiago, Chile |
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| Abstract: | Aging is related to multiple changes in muscle physiology and function. Previous findings concerning the effects of aging on motor unit discharge rate (DR) and fluctuations in DR and force are somewhat contradictory. Eight YOUNG and nine OLD physically active males performed isometric ramp (RECR) and isotonic (ISO) plantar flexions at 10 and 20% of surface EMG at MVC. Motor unit (MU) action potentials were recorded with intramuscular fine-wire electrodes and decomposed with custom build software “Daisy”. DR was lower in OLD in RECR-10% (17.9%, p < 0.001), RECR-20% (15.8%, p < 0.05), ISO-10% (17.7%, p < 0.01) and ISO-20% (14%, n.s.). In YOUNG force fluctuations were smaller at ISO-10% (72.1%, p < 0.001) and ISO-20% (55.2%, p < 0.05) which were accompanied with a slight increase in DR variation (n.s.). The observed lower DR in OLD is in line with earlier findings in small distal muscles. Also the larger force fluctuation in OLD was in line with previous studies with smaller hand muscles. These findings suggest that the age-related changes in MU control do exist also in large leg extensors that play an important role in human locomotion and balance control. |
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