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Updated: Jul 1, 2026
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Physiological Recordings of High and Low Output NMJs on the Crayfish Leg Extensor Muscle
Published on: November 17, 2010
Age-related differences in motor unit discharge rate modulation across contraction levels
Christopher D Connelly1, Tamara Valenčič1, Haydn Thomason1
1School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK.
Geroscience
|June 29, 2026
Summary
Aging reduces muscle strength due to differing adaptations in muscles. Older adults show altered motor unit (MU) firing rates and reduced persistent inward currents (PICs) in specific muscles, impacting strength loss.
Area of Science:
- Neurology
- Kinesiology
- Gerontology
Background:
- Age-related strength loss is a significant concern.
- Morphological and neural adaptations contribute to strength decline.
- Muscle-specific differences in these adaptations are not well understood.
Purpose of the Study:
- To investigate age-related changes in motor unit (MU) discharge rate modulation.
- To estimate the contribution of persistent inward currents (PICs) to MU firing across different contraction levels.
- To compare these changes between the tibialis anterior (TA) and vastus lateralis (VL) muscles.
Main Methods:
- Thirty young and thirty older adults performed isometric dorsiflexion and knee extension.
- High-density electromyography (EMG) recorded motor unit (MU) activity during triangular contractions.
- Magnetic resonance imaging (MRI) assessed muscle morphology.
Main Results:
- Older adults had lower strength and different muscle cross-sectional areas.
- Tibialis anterior (TA) MU discharge rate was lower in older adults at all intensities.
- Vastus lateralis (VL) showed lower MU discharge rates only at lower intensities.
- Persistent inward current (PIC) estimates (discharge rate hysteresis) were reduced in older adults, particularly in TA.
- Age-related differences in MU modulation were muscle-specific.
Conclusions:
- Ageing affects motor unit (MU) discharge rate modulation and persistent inward currents (PICs) differently across muscles.
- These muscle-specific neural and morphological changes contribute to age-related strength loss.
- Knee extensors and dorsiflexors exhibit distinct patterns of age-related neuromuscular decline.
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