RESISTANCE TRAINING INCREASES VASTUS LATERALIS MOTOR UNIT FIRING RATES IN YOUNG AND OLD ADULTS

Motor unit firing rates in human muscle can be determined from recordings made with small-diameter microelectrodes inserted directly into the muscle during voluntary contraction. Frequently, these counts are pooled to give an average motor unit firing rate under a given set of conditions. Since the fibers of one motor unit are dispersed among the cells of several others, it is conceivable that discharge rates can be measured in more than one cell from the same unit. If this occurred frequently, the distribution of firing rates could be influenced by those from units counted more than once. Based on literature values, we made the following assumptions: vastus lateralis contains approximately 300 motor units, with an average innervation ratio of 1500. Muscle cell diameter is about 50 to 100 μm and cells are randomly distributed over a motor unit territory of 10 μm diameter. The recording range of a microelectrode is about 600 μm. Given the distribution of cells normally found in whole human muscle, the probability of recording from two or more cells of the same motor unit at 50% MVC follows a Poisson distribution with a mean of 0.44. This model suggests that although there is a low probability of some duplication in this technique, the extent to which it influences the distribution of average motor unit firing rates is minimal over the entire range of forces produced by vastus lateralis. Key words: probability, motor unit, single unit recording, human muscle, rate coding

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Eight weeks of resistance training increases strength, muscle cross-sectional area and motor unit size, but does not alter firing rates in the vastus lateralis

European Journal of Applied Physiology ◽

10.1007/s00421-019-04273-9 ◽

2019 ◽

Vol 120 (1) ◽

pp. 281-294 ◽

Cited By ~ 2

Author(s):

Adam J. Sterczala ◽

Jonathan D. Miller ◽

Hannah L. Dimmick ◽

Mandy E. Wray ◽

Michael A. Trevino ◽

...

Keyword(s):

Resistance Training ◽

Motor Unit ◽

Vastus Lateralis ◽

Cross Sectional Area ◽

Unit Size ◽

Sectional Area ◽

Cross Sectional ◽

Firing Rates ◽

Muscle Cross Sectional Area

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Anconeus motor unit firing rates during isometric and muscle-shortening contractions comparing young and very old adults

Journal of Neurophysiology ◽

10.1152/jn.00219.2021 ◽

2021 ◽

Vol 126 (4) ◽

pp. 1122-1136

Author(s):

Eric A. Kirk ◽

Kevin J. Gilmore ◽

Charles L. Rice

Keyword(s):

Motor Unit ◽

Elbow Extension ◽

Neural Drive ◽

Younger Adults ◽

Old Adults ◽

Firing Rates ◽

Motor Unit Firing ◽

Muscle Shortening ◽

Adult Aging ◽

Shortening Contractions

Changes of neural drive to the muscle with adult aging, measured as motor unit firing rates during limb movements, are unknown. Throughout maximal voluntary efforts we found that, in comparison with young adults, firing rates were lower during isometric contraction in older adults but not different during elbow extension movements. Despite the older group being ∼33% weaker across contractions, their muscles can receive neural drive during movements that are similar to that of younger adults.

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