Agonist-antagonist common drive during fatiguing knee extension efforts using surface electromyography

Area of Science:

• Biomechanics
• Neurophysiology
• Exercise Physiology

Background:

• Understanding muscle fatigue mechanisms is crucial for optimizing training and rehabilitation.
• Electromyographic (EMG) activity provides insights into muscle activation patterns during exertion.

Purpose of the Study:

• To investigate the electromyographic (EMG) activity of knee extensor agonist and antagonist muscles during fatiguing isometric contractions.
• To analyze EMG parameters like RMS amplitude and frequency spectrum compression across various force levels (25-100% MVC).

Main Methods:

• Five female subjects performed isometric knee extensions at 25%, 50%, 75%, and 100% of maximal voluntary contraction (MVC).
• Surface EMG (SEMG) was recorded from vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), and biceps femoris (BF).
• Root-mean-squared (RMS) amplitude and frequency spectrum compression were calculated; commonality and crosstalk were assessed.

Main Results:

• SEMG RMS amplitude increased with fatigue at 25-75% MVC but decreased at 100% MVC.
• Significant frequency spectrum compression occurred in all recorded muscles across all % MVC levels.
• Vastus medialis (VM), vastus lateralis (VL), and biceps femoris (BF) showed similar responses to fatigue, while rectus femoris (RF) exhibited greater frequency compression.

Conclusions:

• Knee extensor muscles (VM, VL, RF, BF) demonstrate parallel fatigue patterns.
• High similarity in fatigue response between VM, VL, and BF supports the hypothesis of a shared agonist-antagonist motoneuron pool.
• Findings contribute to understanding neuromuscular control during fatiguing contractions.