Multiple motor point stimulation increases tetanic knee torque versus conventional single- electrode functional electrical stimulation: implications for functional output and neurorehabilitation

Background Functional electrical stimulation (FES) delivers transcutaneous electrical current to motor nerves to artificially evoke muscle contractions and produce joint torque. In neurorehabilitation, FES is commonly applied via a large surface electrode pair placed over a muscle group – an approach that we here refer to as single-electrode stimulation (SES). However, the torque-generating capacity of SES is limited. Targeting specific regions of high electrical excitability, or motor points, may enhance neuromuscular activation and increase joint torque output. Here we tested whether continuous multiple motor point stimulation (mMPS) increases tetanic knee torque compared with SES in the quadriceps and hamstrings. We also quantified quadriceps recruitment overlap as a secondary aim. We evaluated quadriceps and hamstring responses to mMPS and SES in neurologically intact participants, recording tetanic knee torque and assessing recruitment overlap relative to maximal voluntary contraction (MVC). Results Stimulating all quadriceps motor points produced approximately 51% greater knee extension torque than SES (33.3% MVC vs. 22.1% MVC). In contrast, stimulating all hamstring motor points did not significantly increase knee flexion torque. Within the quadriceps, proximal and intermediate vastus lateralis motor points contributed the most to knee extension torque, whereas the distal motor point had no significant effect. Discrepancies between observed and predicted MPS torques were primarily associated with rectus femoris stimulation, while vastus medialis contributed the least. Conclusions Stimulation of all quadriceps motor points generated 51% greater knee extension torque compared with conventional SES, highlighting the potential of mMPS to improve the effectiveness of FES interventions. Optimization of motor point selection should emphasize proximal and intermediate vastus lateralis sites, while also including vastus medialis. Rectus femoris stimulation should be considered only when channel allocation permits and when the torque benefit outweighs redundancy. In contrast, hamstring stimulation did not yield additional knee flexion torque underscoring muscle-specific limitations. These findings provide practical guidance for electrode placement and channel allocation, suggesting that optimal quadriceps stimulation can be achieved by prioritizing a limited subset of motor points.