Effects of multiple motor point stimulation on knee joint torque compared with conventional functional electrical...

Area of Science:

• Biomechanics
• Neurorehabilitation
• Biomedical Engineering

Background:

• Functional electrical stimulation (FES) uses transcutaneous electrical current to evoke muscle contractions and joint torque.
• Conventional single-electrode stimulation (SES) has limitations in torque generation, potentially due to fixed recruitment of motor units.
• Targeting specific motor points may enhance neuromuscular activation and increase torque output.

Purpose of the Study:

• To compare the effectiveness of multiple motor point stimulation (mMPS) versus single-electrode stimulation (SES) in generating knee torque.
• To evaluate the torque-generating capacity of stimulating multiple motor points in the quadriceps and hamstring muscles.
• To investigate muscle-specific responses and discrepancies in predicted versus observed torque with mMPS.

Main Methods:

• Twelve neurologically-intact participants underwent mMPS and SES of quadriceps and hamstring muscles.
• Isometric tetanic knee torque was measured and compared to maximal voluntary contraction (MVC).
• Secondary analyses quantified torque prediction discrepancies and MPS contribution to knee extension.

Main Results:

• mMPS of quadriceps yielded ~51% greater knee extension torque than SES (33.3% MVC vs. 22.1% MVC).
• mMPS of hamstrings did not significantly increase knee flexion torque compared to SES (18.4% MVC vs. 21.0% MVC).
• Torque prediction discrepancies were linked to rectus femoris stimulation; vastus medialis showed the least contribution.

Conclusions:

• Stimulating multiple quadriceps motor points enhances knee extension torque more than conventional SES, improving FES effectiveness.
• Hamstring stimulation did not provide additional knee flexion torque, indicating muscle-specific limitations.
• Findings guide electrode placement for quadriceps and suggest prioritizing specific motor points for refined FES strategies.