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Amplitude of the surface electromyogram during fatiguing isometric contractions
Muscle & Nerve
|July 1, 1979
Summary
Muscle strength and surface electromyogram (EMG) amplitude decline during sustained isometric handgrip contractions. Strength loss outpaced EMG changes at lower intensities, while at higher intensities, EMG remained stable despite significant strength decline.
Area of Science:
- Physiology
- Neuromuscular Function
- Biomechanics
Background:
- Sustained submaximal contractions lead to muscle fatigue.
- The relationship between electromyogram (EMG) amplitude and muscle force during fatigue is complex.
- Understanding these relationships is crucial for assessing muscle function and fatigue.
Purpose of the Study:
- To investigate the relationship between surface electromyogram (EMG) amplitude and muscle strength during sustained isometric handgrip contractions.
- To determine how EMG amplitude changes relative to strength decline at different submaximal contraction intensities.
Main Methods:
- Five healthy volunteers performed isometric handgrip contractions at various submaximal tensions.
- Surface EMG amplitude and maximal voluntary contraction (MVC) strength were recorded.
- Intermittent maximal efforts were used to assess strength decline during sustained contractions.
Main Results:
- Initially, EMG amplitude was linearly related to exerted tension.
- During sustained contractions, EMG amplitude increased by approximately 30% of maximum.
- At 25% MVC, strength declined faster than EMG amplitude.
- At 70% MVC, EMG amplitude showed no decline, while muscle strength decreased linearly.
Conclusions:
- Muscle strength declines linearly during sustained submaximal isometric contractions.
- The relationship between EMG amplitude and strength changes dynamically during fatigue.
- At higher contraction intensities, EMG amplitude may not accurately reflect the decline in muscle strength during fatigue.