HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Submit a response Alert me when this article is cited Alert me when Rapid Responses are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by McComas, A. J Articles by de Bruin, H. Search for Related Content PubMed PubMed Citation Articles by McComas, A. J Articles by de Bruin, H. Related Collections Anatomy and Physiology: Musculoskeletal System Amyotrophic Lateral Sclerosis Motor Control and Motor Learning Poliomyelitis/Postpolio Social Bookmarking                      What's this?

Motor Unit Populations in Healthy and Diseased Muscles

AJ McComas, MB, FRCP(C), is Professor and Chair, Department of Biomedical Sciences (Room 4N83), McMaster Health Sciences Centre, McMaster University, 1200 Main St W, Hamilton, Ontario, Canada L8N 3Z5.
V Galea, MSc, is Assistant Professor, School of Occupational and Physical Therapy, McMaster University.
H de Bruin, PhD, is Associate Professor, Department of Medicine, McMaster University.

The numbers of functioning motor units can be estimated in proximal and distal muscles of human limbs by an electrophysiological technique in which the mean sizes of the motor unit potentials are compared with the maximum M-waves of the same muscles. Although manual methods of estimation have been used successfully in the past, the introduction of automated techniques has brought considerable advantages, including greater objectivity and reduced contamination of the results by "alternation." In healthy subjects, the intrinsic muscles of the hand have approximately 100 motor units each, and the biceps brachii muscle has only slightly more. With advancing age, there is a loss of motor units, which appears to be more pronounced in distal muscles. The motor unit estimating methodology has been found to be of value in the diagnosis and assessment of patients suspected of having muscle denervation. In amyotrophic lateral sclerosis, the mean rate of motor unit loss is swift, whereas in late-onset cases of spinal muscular atrophy, the reduction in the motor unit population does not appear to progress. In only the most rapidly deteriorating cases of post-polio syndrome is it possible to demonstrate further loss of motor units. In all of these denervating disorders, and in peripheral neuropathies, the importance of collateral reinnervation as a compensatory mechanism is emphasized.

Key Words: Aging • Amyotrophic lateral sclerosis • Electromyography • Motor units • Poliomyelitis

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				C. A. Knight and G. Kamen Modulation of motor unit firing rates during a complex sinusoidal force task in young and older adults J Appl Physiol, January 1, 2007; 102(1): 122 - 129. [Abstract] [Full Text] [PDF]

				B. M. Prior, J. M. Foley, R. C. Jayaraman, and R. A. Meyer Pixel T2 distribution in functional magnetic resonance images of muscle J Appl Physiol, December 1, 1999; 87(6): 2107 - 2114. [Abstract] [Full Text] [PDF]

				T. J. Doherty and W. F. Brown Age-related changes in the twitch contractile properties of human thenar motor units J Appl Physiol, January 1, 1997; 82(1): 93 - 101. [Abstract] [Full Text] [PDF]