Vastus Lateralis Motor Unit Recruitment Thresholds Are Compressed towards Lower Forces in Older Men
R M Girts1, J A Mota, K K Harmon
1Matt S. Stock, Ph.D., School of Kinesiology and Physical Therapy, University of Central Florida, 12805 Pegasus Drive, HPA 1 - Room 258, Orlando, FL 32816-2205, Phone: (407) 823-0364, Fax: (407) 823-2596,
The Journal of Frailty & Aging
|September 30, 2020
Summary
Older men recruit more motor units at lower force levels, suggesting neural adaptations in motor unit control with aging. This may compensate for reduced firing rates or muscle changes.
Area of Science:
- Neurology
- Kinesiology
- Gerontology
Background:
- Aging leads to physiological changes that can impact motor unit control.
- Understanding age-related motor unit adaptations is crucial for maintaining mobility and function.
Purpose of the Study:
- To investigate whether younger and older men recruit motor units at comparable force levels.
- To analyze age-related differences in motor unit recruitment thresholds and firing characteristics.
Main Methods:
- A cross-sectional study comparing 12 younger (25±3 years) and 12 older (75±8 years) men.
- Isometric knee extensor contractions at 50% maximal voluntary contraction (MVC).
- Surface electromyography (EMG) and signal decomposition to determine motor unit recruitment thresholds and firing rates.
Main Results:
- Older men exhibited lower absolute and relative recruitment thresholds compared to younger men.
- Younger men had a wider absolute recruitment threshold range.
- Older men showed a flatter slope and lower y-intercept in the mean firing rate versus recruitment threshold relationship.
Conclusions:
- Older adults tend to recruit more motor units at lower force levels.
- This suggests potential neural adaptations, possibly "recruitment threshold compression," in aging.
- These adaptations may help compensate for reduced motor unit firing rates or muscle denervation/re-innervation processes.
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