Motor unit recruitment and firing rate at low force of contraction. Muscle Nerve 2022 Dec;66(6):750-756
Date
10/11/2022Pubmed ID
36214178DOI
10.1002/mus.27737Scopus ID
2-s2.0-85140235887 (requires institutional sign-in at Scopus site) 2 CitationsAbstract
INTRODUCTION/AIMS: A prevailing concept of motor unit (MU) recruitment used for calculating recruitment ratio (RR) suggests a progressive linear increase in firing rate (FR). The objective of this study is to assess its validity.
METHODS: Concentric needle electromyography (EMG) recordings were made in normal muscle and abnormal muscle of patients with neurogenic findings. Signals recorded at low force were visually decomposed to study MU FR at onset, recruitment of a second MU, and recruitment of more MUs with further increases in force.
RESULTS: We observed one to six MUs discharging at a rate < 15 Hz in normal muscles at low force. The MU FR was 5-8 Hz at onset. With increasing force, FR increased by 3-5 Hz and then idled at <15 Hz while other MUs were recruited. The recruitment frequency (RF) and RR had low sensitivity and were abnormal mainly in moderately to severely weak muscles.
DISCUSSION: Our data are consistent with FR analysis results described by other investigators. It does not support a progressive linear increase in MU FR with recruitment. A revised model for MU recruitment at low effort during gradual increase in force is presented. On subjective assessment, the FR of the fastest firing MU can help detect MU loss in neurogenic processes.
Author List
Nandedkar SD, Barkhaus PE, Stålberg EVAuthor
Paul E. Barkhaus MD Professor in the Neurology department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
ElectromyographyHumans
Isometric Contraction
Motor Neurons
Muscle Contraction
Muscle, Skeletal
Muscles
Recruitment, Neurophysiological
