Influence of timing variability between motor unit potentials on M-wave characteristics |
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| Institution: | 1. Department of Electrical and Electronical Engineering, Public University of Navarra, Pamplona, Spain;2. Pediatric Neurology Unit, Virgen del Camino Hospital, Pamplona, Spain;1. Biomechanics and Sport Performance Laboratory, California State University, San Bernardino, San Bernardino, CA 92407, United States;2. Sensory and Muscle Function Laboratory, The University of Oklahoma, Norman, OK 73019, United States;3. Applied Biomechanics Laboratory, The University of Mississippi, University, MS 38677, United States;4. Department of Kinesiology and Health Promotion, Troy University, Troy, AL 36081, United States;1. Private practice, Chesterfield, MO, United States;2. University of Missouri-Kansas City, School of Dentistry, Kansas City, MO, United States;3. East Tennessee State University, College of Public Health, Johnson City, TN, United States;4. Texas A & M University, Baylor College of Dentistry, Dallas, TX, United States;5. University of Nebraska Medical Center, College of Dentistry, Lincoln, NE, United States;1. Laboratory of Biomechanics and Clinical Epidemiology, PAIFIT Research Group, Universidade Estadual de Londrina, Londrina, PR, Brazil;2. Universidade Federal do Vale do São Francisco, Colegiado de Educação Física, Petrolina, PE, Brazil;3. Faculdade Assis Gurgacz, Cascavel, PR, Brazil;4. Instituto Federal do Paraná, Londrina, PR, Brazil;5. Institute of Nursing and Health Research, School of Health Sciences, Ulster University, Belfast, Northern Ireland, UK;6. Sports Sciences Department, Universidade Estadual de Londrina, Londrina, PR, Brazil;7. Aquatic Physical Therapy Center “Prof. Paulo A. Seibert”, University Hospital, Universidade Estadual de Londrina, Londrina, PR, Brazil |
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| Abstract: | The transient enlargement of the compound muscle action potential (M wave) after a conditioning contraction is referred to as potentiation. It has been recently shown that the potentiation of the first and second phases of a monopolar M wave differed drastically; namely, the first phase remained largely unchanged, whereas the second phase underwent a marked enlargement and shortening. This dissimilar potentiation of the first and second phases has been suggested to be attributed to a transient increase in conduction velocity after the contraction. Here, we present a series of simulations to test if changes in the timing variability between motor unit potentials (MUPs) can be responsible for the unequal potentiation (and shortening) of the first and the second M-wave phases. We found that an increase in the mean motor unit conduction velocity resulted in a marked enlargement and narrowing of both the first and second M-wave phases. The enlargement of the first phase caused by a global increase in motor unit conduction velocities was apparent even for the electrode located over the innervation zone and became more pronounced with increasing distance to the innervation zone, whereas the potentiation of the second phase was largely independent of electrode position. Our simulations indicate that it is unlikely that an increase in motor unit conduction velocities (accompanied or not by changes in their distribution) could account for the experimental observation that only the second phase of a monopolar M wave, but not the first, is enlarged after a brief contraction. However, the combination of an increase in the motor unit conduction velocities and a spreading of the motor unit activation times could potentially explain the asymmetric potentiation of the M-wave phases. |
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| Keywords: | Electromyogram Motor unit potentials Compound muscle action potential M-wave potentiation Conduction velocity |
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