Firing behavior of single motor units of the tibialis anterior in human walking as non-invasively revealed by HDsEMG decomposition

Hikaru Yokoyama; Naotsugu Kaneko; Atsushi Sasaki; Akira Saito; Kimitaka Nakazawa

doi:10.1088/1741-2552/aca71b

Firing behavior of single motor units of the tibialis anterior in human walking as non-invasively revealed by HDsEMG decomposition

J Neural Eng. 2022 Dec 14;19(6). doi: 10.1088/1741-2552/aca71b.

Authors

Hikaru Yokoyama^{1

2}, Naotsugu Kaneko^{2

3

4}, Atsushi Sasaki^{2

3

5}, Akira Saito⁶, Kimitaka Nakazawa²

Affiliations

¹ Institute of Engineering, Tokyo University of Agriculture and Technology, Tokyo 184-8588, Japan.
² Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan.
³ Japan Society for the Promotion of Science, Tokyo 102-0083, Japan.
⁴ Department of Neuropsychiatry, Keio University School of Medicine, Tokyo 160-8582, Japan.
⁵ Graduate School of Engineering Science, Department of Mechanical Science and Bioengineering, Osaka University, Osaka 560-8531, Japan.
⁶ Center for Health and Sports Science, Kyushu Sangyo University, Fukuoka 813-8503, Japan.

PMID: 36541453
DOI: 10.1088/1741-2552/aca71b

Abstract

Objective.Investigation of the firing behavior of motor units (MUs) provides essential neuromuscular control information because MUs are the smallest organizational component of the neuromuscular system. The MUs activated during human infants' leg movements and rodent locomotion, mainly controlled by the spinal central pattern generator (CPG), show highly synchronous firing. In addition to spinal CPGs, the cerebral cortex is involved in neuromuscular control during walking in human adults. Based on the difference in the neural control mechanisms of locomotion between rodent, human infants and adults, MU firing behavior during adult walking probably has some different features from the other populations. However, so far, the firing activity of MUs in human adult walking has been largely unknown due to technical issues.Approach.Recent technical advances allow noninvasive investigation of MU firing by high-density surface electromyogram (HDsEMG) decomposition. We investigated the MU firing behavior of the tibialis anterior (TA) muscle during walking at a slow speed by HDsEMG decomposition.Main results.We found recruitment threshold modulation of MU between walking and steady isometric contractions. Doublet firings, and gait phase-specific firings were also observed during walking. We also found high MU synchronization during walking over a wide range of frequencies, probably including cortical and spinal CPG-related components. The amount of MU synchronization was modulated between the gait phases and motor tasks. These results suggest that the central nervous system flexibly controls MU firing to generate appropriate force of TA during human walking.Significance.This study revealed the MU behavior during walking at a slow speed and demonstrated the feasibility of noninvasive investigation of MUs during dynamic locomotor tasks, which will open new frontiers for the study of neuromuscular systems in the fields of neuroscience and biomedical engineering.

Keywords: EMG; motor units; muscle; spinal motor neurons; walking.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adult
Electromyography / methods
Humans
Isometric Contraction / physiology
Locomotion
Motor Neurons* / physiology
Muscle Contraction / physiology
Muscle, Skeletal* / physiology
Walking