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

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, possibly due to spatial-fixation of recruited motor units. Targeting specific regions of high electrical excitability, or motor points, may enhance neuromuscular activation and increase joint torque output.

METHODS

Twelve neurologically-intact participants underwent both continuous multiple motor point stimulation (mMPS) and SES of the quadriceps and hamstring muscle groups. Isometric tetanic knee torque was evaluated and compared relative to maximal voluntary contraction (MVC). As secondary aims, we quantified the discrepancy between observed and predicted torque response and the relative contribution of MPS conditions to knee extension torque.

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 (18.4% MVC) did not significantly increase knee flexion torque compared to SES (21.0% MVC). 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 greater knee extension torque compared with conventional SES, highlighting the potential of mMPS to improve the effectiveness of FES interventions. In contrast, hamstring stimulation did not yield additional knee flexion torque underscoring muscle-specific limitations. These findings provide practical guidance for quadriceps electrode placement and channel allocation, indicating that more refined FES strategies can be achieved by prioritizing a targeted subset of motor points.