The reliability of methods to estimate the number and size of human motor units and their use with large limb muscles

Piasecki, M. ORCID: 0000-0002-7804-4631, Ireland, A., Piasecki, J. ORCID: 0000-0001-9758-6295, Stashuk, D.W., McPhee, J.S. and Jones, D.A., 2018. The reliability of methods to estimate the number and size of human motor units and their use with large limb muscles. European Journal of Applied Physiology, 118 (4), pp. 767-775. ISSN 1439-6319

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Purpose: Current methods for estimating muscle motor unit (MU) number provide values which are remarkably similar for muscles of widely differing size, probably because surface electrodes sample from similar and relatively small volumes in each muscle. We have evaluated an alternative means of estimating MU number that takes into account differences in muscle size.

Methods: Intramuscular motor unit potentials (MUPs) were recorded and muscle cross-sectional area (CSA) was measured using MRI to provide a motor unit number estimate (iMUNE). This was compared to the traditional MUNE method, using compound muscle action potentials (CMAP) and surface motor unit potentials (sMUPs) recorded using surface electrodes. Data were collected from proximal and distal regions of the vastus lateralis (VL) in young and old men while test–retest reliability was evaluated with VL, tibialis anterior and biceps brachii.

Results: MUPs, sMUPs and CMAPs were highly reliable (r = 0.84–0.91). The traditional MUNE, based on surface recordings, did not differ between proximal and distal sites of the VL despite the proximal CSA being twice the distal CSA. iMUNE, however, gave values that differed between young and old and were proportional to the muscle size.

Conclusion: When evaluating the contribution that MU loss makes to muscle atrophy, such as in disease or ageing, it is important to have a method such as iMUNE, which takes into account any differences in total muscle size.

Item Type: Journal article
Publication Title: European Journal of Applied Physiology
Creators: Piasecki, M., Ireland, A., Piasecki, J., Stashuk, D.W., McPhee, J.S. and Jones, D.A.
Publisher: Springer
Date: April 2018
Volume: 118
Number: 4
ISSN: 1439-6319
3811Publisher Item Identifier
Rights: © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Divisions: Schools > School of Science and Technology
Record created by: Linda Sullivan
Date Added: 28 Jun 2018 08:27
Last Modified: 28 Jun 2018 08:27

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