Motor Unit Number Estimation of the Second Lumbrical Muscle in Human Hand.

Ya Zong,Ping Zhou,Zhiyuan Lu,Lianfu Deng,Maoqi Chen,Qin Xie

doi:10.3389/fphys.2022.854385

Ya Zong, Ping Zhou + Show 4 more

Open Access

https://doi.org/10.3389/fphys.2022.854385

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Abstract

The number of motor units of the lumbrical muscles in human hand has not been explored. The objective of this study was to fill this gap by estimating the number of motor units in the second lumbrical muscle. Compound muscle action potential scan of the second lumbrical muscle was performed in 12 healthy subjects, with 10 of them being tested on two separate occasions. Motor unit number estimation (MUNE) was derived from the MScanFit program. The average MUNE of the second lumbrical muscle was 41.6 ± 2.1 (mean ± standard error) from 12 subjects in the first test, and 42.0 ± 2.2 from 10 of the 12 subjects in the retest, demonstrating excellent measurement reliability. Findings of the study provide novel information about the motor unit number of the second lumbrical muscle in human hand. The relatively low motor unit number in the muscle can facilitate motor unit investigations, especially at high level muscle activation.

Highlights

The human hand lumbrical muscles include four short intrinsic muscles, attached proximally to the tendons of flexor digitorum profundus and distally to the extensor expansions (Gosling et al, 2008)
The difference between the median motor latency to the second lumbrical muscle and the ulnar motor latency to the interossei muscles is sensitive for diagnosis of different grades of in carpal tunnel syndrome (Brannegan and Bartt, 2007; Meena et al, 2008; Kodama et al, 2012; Ozben et al, 2012)
This study presents a novel application of MScanFit Motor unit number estimation (MUNE), and for the first time provides information about motor unit number in the lumbrical muscle, which is largely unexplored in previous literature

Summary

Introduction

The human hand lumbrical muscles include four short intrinsic muscles, attached proximally to the tendons of flexor digitorum profundus and distally to the extensor expansions (Gosling et al, 2008). The first and second lumbrical muscles (innervated by the median nerve) arise from the radial side of the most radial tendons of the flexor digitorum profundus, corresponding to the index finger and the middle finger, respectively. The function of the lumbrical muscles is to flex the metacarpophalangeal joints and extend both the proximal and distal interphalangeal joints. These actions are involved in complex hand movement, contributing to hand dexterity (Palti and Vigler, 2012). The difference between the median motor latency to the second lumbrical muscle and the ulnar motor latency to the interossei muscles is sensitive for diagnosis of different grades of in carpal tunnel syndrome (Brannegan and Bartt, 2007; Meena et al, 2008; Kodama et al, 2012; Ozben et al, 2012)

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