Does the frequency content of the surface mechanomyographic signal reflect motor unit firing rates? A brief review

Beck, Travis W.; Housh, Terry J.; Johnson, Glen O.; Cramer, Joel T.; Weir, Joseph P.; Coburn, Jared W.; Malek, Moh H.

doi:10.1016/j.jelekin.2005.12.002

Next »Journal of Electromyography and Kinesiology
Volume 17, Issue 1 , Pages 1-13, February 2007

Does the frequency content of the surface mechanomyographic signal reflect motor unit firing rates? A brief review

Travis W. Beck
- Department of Nutrition and Health Sciences, Human Performance Laboratory, University of Nebraska-Lincoln, 104K Ruth Leverton Hall, Lincoln, NE 68583-0806, United States
- Corresponding author. Tel.: +1 402 472 2690; fax: +1 402 472 0522.
Terry J. Housh
- Department of Nutrition and Health Sciences, Human Performance Laboratory, University of Nebraska-Lincoln, 104K Ruth Leverton Hall, Lincoln, NE 68583-0806, United States
Glen O. Johnson
- Department of Nutrition and Health Sciences, Human Performance Laboratory, University of Nebraska-Lincoln, 104K Ruth Leverton Hall, Lincoln, NE 68583-0806, United States
Joel T. Cramer
- Department of Health and Exercise Science, University of Oklahoma, Norman, OK 73019, United States
Joseph P. Weir
- Applied Physiology Laboratory, Division of Physical Therapy, Des Moines University Osteopathic Medical Center, Des Moines, IA 50312, United States
Jared W. Coburn
- Department of Nutrition and Health Sciences, Human Performance Laboratory, University of Nebraska-Lincoln, 104K Ruth Leverton Hall, Lincoln, NE 68583-0806, United States
Moh H. Malek
- Department of Nutrition and Health Sciences, Human Performance Laboratory, University of Nebraska-Lincoln, 104K Ruth Leverton Hall, Lincoln, NE 68583-0806, United States

Received 22 August 2005; received in revised form 8 December 2005; accepted 18 December 2005. published online 23 February 2006.

Abstract

The purpose of this review is to examine the literature that has investigated the potential relationship between mechanomyographic (MMG) frequency and motor unit firing rates. Several different experimental designs/methodologies have been used to address this issue, including: repetitive electrical stimulation, voluntary muscle actions in muscles with different fiber type compositions, fatiguing and non-fatiguing isometric or dynamic muscle actions, and voluntary muscle actions in young versus elderly subjects and healthy individuals versus subjects with a neuromuscular disease(s). Generally speaking, the results from these investigations have suggested that MMG frequency is related to the rate of motor unit activation and the contractile properties (contraction and relaxation times) of the muscle fibers. Other studies, however, have reported that MMG mean power frequency (MPF) does not always follow the expected pattern of firing rate modulation (e.g. motor unit firing rates generally increase with torque during isometric muscle actions, but MMG MPF may remain stable or even decrease). In addition, there are several factors that may affect the frequency content of the MMG signal during a voluntary muscle action (i.e. muscle stiffness, intramuscular fluid pressure, etc.), independent of changes in motor unit firing rates. Despite the potential influences of these factors, most of the evidence has suggested that the frequency domain of the MMG signal contains some information regarding motor unit firing rates. It is likely, however, that this information is qualitative, rather than quantitative in nature, and reflects the global motor unit firing rate, rather than the firing rates of a particular group of motor units.

Keywords: Mechanomyography, Motor unit firing rates, Motor control strategies