Wrist torque estimation during simultaneous and continuously changing movements: surface vs. untargeted intramuscular...

Area of Science:

• Biomedical Engineering
• Neuroscience
• Rehabilitation Technology

Background:

• Accurate electromyography (EMG) signal interpretation is crucial for advanced prosthetic limb control.
• Understanding the predictive capability of different EMG measurement types for joint torque is essential for improving prosthetic functionality.

Purpose of the Study:

• To compare the predictive accuracy of surface EMG versus intramuscular EMG for wrist-joint torque.
• To determine which EMG measurement technique better represents joint torque during multi-degree-of-freedom (DoF) movements.
• To assess the potential application of these EMG methods in prosthetic control systems.

Main Methods:

• Concurrent recording of surface and intramuscular EMG from the forearm of ten able-bodied subjects.
• Subjects performed single and combined DoF wrist movements while tracking continuous contraction profiles.
• Artificial neural networks were used to assess the association between EMG signals and measured wrist-joint torque.

Main Results:

• Surface EMG demonstrated superior performance over intramuscular EMG across all metrics (R(2), PCC, RMSE).
• Surface EMG achieved higher coefficient of determination (R(2) = 0.93) and Pearson correlation coefficient (PCC = 0.98), with lower root mean square error (RMSE = 8.7%).
• Intramuscular EMG showed lower predictive accuracy (R(2) = 0.80, PCC = 0.93, RMSE = 14.5%), potentially due to high signal selectivity.

Conclusions:

• Surface EMG offers a more robust and accurate representation of wrist-joint torque compared to intramuscular EMG for prosthetic control.
• While both methods track torque profiles, surface EMG is more reliable for estimating torque amplitude.
• The high selectivity of intramuscular EMG recordings may limit its performance in dynamic, multi-DoF movement applications.