Muscle fatigue assessment during sustained high isometric contractions

Area of Science:

• Neuromuscular Physiology
• Biomedical Engineering
• Exercise Science

Background:

• Muscle fatigue is a complex physiological phenomenon affecting performance.
• Surface electromyography (sEMG) offers a non-invasive method to study muscle fatigue.
• Understanding the electromyographical changes associated with fatigue is crucial for optimizing training and rehabilitation.

Purpose of the Study:

• To evaluate the myoelectrical manifestations of muscle fatigue during isometric contractions.
• To determine the most appropriate sEMG-derived parameter for assessing muscle fatigue.
• To compare the fatigue patterns between maximal and submaximal contractions.

Main Methods:

• Surface electromyography (sEMG) was recorded from the biceps brachii during isometric contractions.
• Level-trigger averaging was used to analyze the myoelectrical signals.
• Conduction velocity (CV), amplitude, and duration of action potentials were calculated.
• Contractions were performed at maximal (MVC) and submaximal (75% MVC) intensities.

Main Results:

• Conduction velocity (CV) emerged as the most suitable sEMG parameter for muscle fatigue assessment.
• The endurance time and CV changes during submaximal contractions closely matched those during maximal contractions (up to 30% torque reduction).
• Motor unit (MU) recruitment during sustained contractions did not significantly alter calculated CV values.

Conclusions:

• Surface electromyography (sEMG) and specifically conduction velocity (CV) provide a reliable measure of muscle fatigue.
• The fatigue progression, as indicated by CV, is similar across different contraction intensities.
• These findings support the use of CV for monitoring muscle fatigue in both maximal and submaximal exercise scenarios.