Journal
EXPERIMENTAL BRAIN RESEARCH
Volume 239, Issue 2, Pages 463-474Publisher
SPRINGER
DOI: 10.1007/s00221-020-05973-x
Keywords
Corticospinal excitability; Posterior root-muscle reflex; Electromyography; Quadriceps femoris; Spinal cord stimulation
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Funding
- JSPS KAKENHI [JP17J02997, 18H04082]
- Grants-in-Aid for Scientific Research [18H04082] Funding Source: KAKEN
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The study found that voluntary muscle contraction affects the excitabilities of corticospinal and spinal reflex circuits in lower-limb muscles, with differences observed among different muscles. MEP and posterior root-muscle reflex amplitudes of agonists increased with increasing torque levels, while MEP amplitudes of antagonists were also influenced. The modulation of corticospinal and spinal reflex circuit excitabilities during agonist and antagonist muscle contractions varied across lower-limb muscles.
Voluntary contraction facilitates corticospinal and spinal reflex circuit excitabilities of the contracted muscle and inhibits spinal reflex circuit excitability of the antagonist. It has been suggested that modulation of spinal reflex circuit excitability in agonist and antagonist muscles during voluntary contraction differs among lower-limb muscles. However, whether the effects of voluntary contraction on the excitabilities of corticospinal and spinal reflex circuits depend on the tested muscles remains unknown. The purpose of this study was to examine inter-muscle differences in modulation of the corticospinal and spinal reflex circuit excitabilities of multiple lower-limb muscles during voluntary contraction. Eleven young males performed isometric plantar-flexion, dorsi-flexion, knee extension, and flexion at low torque levels. Motor evoked potentials (MEPs) and posterior root-muscle reflexes from seven lower-leg and thigh muscles were evoked by transcranial magnetic stimulation and transcutaneous spinal cord stimulation, respectively, at rest and during weak voluntary contractions. MEP and posterior root-muscle reflex amplitudes of agonists were significantly increased as agonist torque level increased, except for the reflex of the tibialis anterior. MEP amplitudes of antagonists were significantly increased in relation to the agonist torque level, but those of the rectus femoris were slightly depressed during knee flexion. Regarding the posterior root-muscle reflex of the antagonists, the amplitudes of triceps surae and the hamstrings were significantly decreased, but those of the quadriceps femoris were significantly increased as the agonist torque level increased. These results demonstrate that modulation of corticospinal and spinal reflex circuit excitabilities during agonist and antagonist muscle contractions differed among lower-limb muscles.
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