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Surface mechanomyogram amplitude is not attenuated by intramuscular pressure
K Søgaard1, C Orizio, G Sjøgaard
1Department of Physiology, National Institute of Occupational Health, Copehangen, Denmark.
European Journal of Applied Physiology
|September 18, 2004
Summary
Intramuscular pressure (IMP) does not hinder mechanomyogram (MMG) signal generation during voluntary contractions. Other factors, like high motor unit firing rates, likely cause the MMG signal to plateau at maximal efforts.
Area of Science:
- Biomechanics
- Human Physiology
- Motor Control
Background:
- Electromyogram (EMG) and intramuscular pressure (IMP) increase linearly with force during static contractions.
- Surface mechanomyogram (MMG) linearity plateaus around 70% of maximal voluntary contraction (MVC).
Purpose of the Study:
- Investigate the influence of IMP on the non-linear MMG force relationship.
- Understand IMP's role in MMG signal generation during voluntary contractions.
Main Methods:
- Seven subjects performed elbow flexor static contractions (ramps and steps) with varying external cuff pressures.
- Measured EMG, MMG (biceps brachii), and IMP using surface electrodes, accelerometer, and pressure transducer.
- Analyzed MMG(rms) and EMG(rms) responses relative to IMP and %MVC.
Main Results:
- IMP showed a strong, linear relationship with external pressure and contraction force.
- Increased IMP did not reduce EMG(rms) or MMG(rms).
- Higher cuff pressure (50 mmHg) during ramp contractions showed a steeper MMG(rms) vs. %MVC relationship.
Conclusions:
- Intramuscular pressure (IMP) does not inherently attenuate MMG signal generation.
- The MMG plateau at high contraction forces is likely due to other factors, such as motor unit firing rate fusion.