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M-wave changes caused by brief voluntary and stimulated isometric contractions
Javier Rodriguez-Falces1, Armando Malanda2, Javier Navallas2
1Department of Electrical and Electronical Engineering, Public University of Navarra, Campus de Arrosadía s/n. 31006, Pamplona, Spain. javier.rodriguez.falces@gmail.com.
European Journal of Applied Physiology
|May 18, 2023
Summary
Muscle shortening during isometric contractions alters the compound muscle action potential (M wave). This study experimentally assessed M-wave changes, revealing significant shifts in amplitude and duration due to muscle contraction.
Area of Science:
- Physiology
- Electromyography
- Muscle Mechanics
Background:
- Muscle force generation under isometric conditions correlates with decreased fiber length.
- Previous research on muscle shortening effects on the M wave relied on computer simulations.
- This study provides the first experimental investigation into M-wave alterations during isometric contractions.
Purpose of the Study:
- To experimentally evaluate changes in the compound muscle action potential (M wave) during brief voluntary and stimulated isometric contractions.
- To quantify the impact of muscle shortening on M-wave amplitude and duration.
- To differentiate M-wave changes caused by muscle shortening from those due to fatigue or ion pump activity.
Main Methods:
- Muscle shortening was induced via brief tetanic contractions (1s) or voluntary contractions of varying intensities.
- Supramaximal stimulation of the brachial plexus and femoral nerves evoked M waves.
- M-wave amplitude and duration of the first and second phases were analyzed during isometric contractions at different force levels (up to 100% MVC).
Main Results:
- Tetanic stimulation led to a decrease in the first M-wave phase amplitude (~10%) and duration (~20%), with an increase in the second phase (~50%).
- Voluntary contractions showed a decrease in the first M-wave phase amplitude (~20%) and duration (~30%), with an increase in the second phase (~30%) as force increased to 60-70% MVC.
- These M-wave modifications stabilized after initial responses during tetanic stimulation.
Conclusions:
- Muscle shortening significantly modifies the M-wave profile, affecting both amplitude and duration.
- The observed M-wave adjustments provide a basis for distinguishing contraction-induced changes from those related to muscle fatigue or Na+-K+ pump activity.
- Experimental data clarifies the physiological responses of the M wave to dynamic changes in muscle length under isometric conditions.
Keywords:
Fascicle lengthFiber diameterIsometric contractionMuscle bulgingMuscle shorteningTetanic stimulationMore Related Videos
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