Decomposition-based quantitative electromyography: effect of force on motor unit potentials and motor unit number...

Area of Science:

• Neuromuscular Physiology
• Quantitative Electromyography

Background:

• Decomposition-based quantitative electromyography (DQEMG) enables motor unit potential (MUP) collection across various force levels.
• The size principle of motor unit recruitment suggests force may influence DQEMG-derived motor unit number estimates (MUNE).

Purpose of the Study:

• To investigate the effect of contraction force on needle- and surface-detected MUP characteristics.
• To determine the impact of force on MUNEs derived using DQEMG in the first dorsal interosseous (FDI) muscle.

Main Methods:

• Simultaneous collection of intramuscular and surface EMG during isometric contractions at varying percentages of maximal voluntary contraction (MVC).
• Application of decomposition algorithms to identify MUPs and their firing times.
• Spike-triggered averaging of surface-detected MUPs (S-MUPs) using identified MUP firing times.
• Calculation of MUNE by dividing maximum M-wave size by mean S-MUP size.

Main Results:

• Increased contraction force significantly altered MUP size and firing rate for both needle and surface recordings.
• Force level demonstrated a significant effect on the calculated MUNE values.
• Both needle-detected MUPs and surface-detected MUPs (S-MUPs) were affected by force.

Conclusions:

• Contraction force is a critical variable to control for when performing quantitative EMG, particularly for MUNE calculations with DQEMG.
• The physiological characteristics of MUPs and resulting MUNEs are force-dependent.
• Future quantitative EMG studies should account for force variations to ensure accurate results.