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Reductions in Motor Unit Firing are Associated with Clinically Meaningful Leg Extensor Weakness in Older Adults
Nathan P Wages1,2,3, Mohamed H Mousa4, Leatha A Clark5,6,7
1Ohio Musculoskeletal and Neurological Institute, Ohio University, 250 Irvine Hall, 1 Ohio University, Athens, OH, 45701, USA. wages@ohio.edu.
Calcified Tissue International
|August 21, 2023
Summary
Reduced motor unit firing rates (MUFRs) are linked to age-related weakness in older adults. This study shows slower MUFRs mechanistically contribute to clinically significant leg extensor weakness.
Area of Science:
- * Physiology and Gerontology
- * Neuromuscular Function and Aging
Background:
- * Sarcopenia, characterized by weakness, is a major risk factor for disability in older adults.
- * Reduced motor unit firing rates (MUFRs) are hypothesized to cause age-related weakness, but direct links to clinical weakness are understudied.
Purpose of the Study:
- * To investigate the association between MUFRs and clinically meaningful leg extensor weakness in older adults.
- * To quantify the impact of slowed MUFRs on strength using computational modeling.
Main Methods:
- * Electromyography (EMG) was used to measure MUFRs in the vastus lateralis of older and young adults during isometric leg extension tasks.
- * Participants performed torque matching at submaximal intensities (50% and 80% maximal voluntary contraction).
- * Computational modeling predicted strength decrements from reduced MUFRs; correlations with physical function were assessed.
Main Results:
- * Weak older adults showed significantly lower MUFRs compared to non-weak older adults and young adults at specific contraction intensities.
- * A 3 Hz reduction in MUFR was predicted to cause an 11-26% decrease in strength.
- * Slower MUFRs correlated with poorer neuromuscular quality, voluntary activation, and reduced performance in functional mobility tests (chair rise, stair climb).
Conclusions:
- * Slowed MUFRs are mechanistically linked to clinically relevant leg extensor weakness in older adults.
- * Findings support MUFR reduction as a key contributor to age-related muscle weakness and functional decline.
