An Electromyographic Study Comparing Muscle Function During Supination and Pronation of the Forearm

Area of Science:

• Biomechanics
• Human Movement Science
• Neurorehabilitation

Background:

• Forearm pronation and supination are crucial for daily activities.
• Muscle activation patterns during forearm rotation under varying loads are not fully understood.
• This knowledge gap impacts rehabilitation, surgery, and prosthetic design.

Purpose of the Study:

• To quantify and compare electromyographic (EMG) activity of forearm rotator muscles.
• To analyze muscle recruitment strategies during isometric pronation and supination under increasing torque loads.

Main Methods:

• Simultaneous surface and fine-wire EMG recordings with motion capture in four healthy subjects.
• Isometric forearm rotation tasks with incrementally increasing torque resistance.
• EMG signal analysis using root mean square values after filtering and normalization.

Main Results:

• Supinator showed higher initial activation than biceps brachii during supination.
• Biceps brachii proportionally increased activation more than supinator with higher torques.
• Pronator quadratus was more active at lower pronation torques; pronator teres increased more with higher torques.
• Multi-joint muscles were progressively recruited with increased torque demands in both movements.

Conclusions:

• Supinator and pronator quadratus are primary muscles for low-torque forearm rotation.
• Biceps brachii and pronator teres become more dominant with increasing torque demands.
• Observed hierarchical recruitment optimizes mechanical efficiency and joint stability, with potential clinical applications in rehabilitation and prosthetics.