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AAEM minimonograph #3: motor unit recruitment.
1Department of Neurology, University of Utah School of Medicine, Salt Lake City.
Muscle & Nerve
|June 1, 1991
Summary
Motor unit recruitment, the activation of motor units for muscle contraction, follows a size principle. Disorders affecting motor units can alter recruitment patterns, impacting muscle force generation and clinical assessment.
Area of Science:
- Neuroscience
- Physiology
- Motor Control
Background:
- Motor unit recruitment is fundamental to muscle contraction, involving the sequential activation of motor units.
- Muscle force is modulated by motoneuron (MN) firing rate (rate coding) and the recruitment of additional motor units.
Purpose of the Study:
- To explain the principles of motor unit recruitment and its regulation.
- To propose a clinical electromyographic method for assessing motor unit recruitment.
Main Methods:
- Review of existing literature on motor unit recruitment and size principle.
- Description of a three-level clinical electromyographic assessment protocol.
Main Results:
- Motor units are recruited in a size-ordered manner, with smaller, slow-twitch units activated first.
- Factors like synaptic density and membrane resistance influence recruitment order.
- Disorders can lead to abnormal recruitment, affecting muscle function and electromyographic patterns.
Conclusions:
- Motor unit recruitment is a size-dependent process influenced by central drive and MN pool organization.
- Clinical electromyography can assess recruitment abnormalities, aiding in the diagnosis of neuromuscular disorders.