Does Electrode Sensor Positioning over Motor Points Affect Different Portions of Quadriceps Muscle Architecture during Submaximal Evoked Torque?

Abstract

Background and Objectives. Few studies have evaluated differences in muscle architecture in quadriceps femoris constituents with sensor electrodes positioned over vastus lateralis (VL) and vastus medialis (VM) motor points during a neuromuscular electrical stimulation (NMES) session. We aimed to investigate the changes in muscle architecture of the rectus femoris (RF), VL, VM, and vastus intermedius (VI) portions during evoked contractions with sensor electrodes placed over VL and VM motor points. Materials and Methods. The study is a crossover, repeated-measure design, conducted with healthy males aged $24.0\pm 4.6$ years. Ultrasonography at rest and evoked contraction at 40% of maximum voluntary contraction (MVC) were used to assess the pennation angle ( $\theta p$ ) and fascicle length (Lf) of RF, VL, VM, and VI portions. Results. The mean torque observed was $201.14\pm 50.22$  N.m during MVC and at 40% of MVC was $80.45\pm 20.08$  N.m. There was no difference for $\theta p$ comparing four components of the quadriceps femoris ( $p=0.27$ ). There was a significant ( $p<0.05$ ) muscle evoked contraction interaction for Lf without relevant clinical importance to the study. Conclusions. There is no difference in the changes in the muscle architecture of quadriceps femoris constituents during stimulation with the electrodes placed on the VL and VM motor points. Therefore, clinicians can choose either VL or VM motor points for sensor electrode positioning and expect similar muscle architecture adaptation for a given evoked torque. Future clinical studies should be conducted to establish the optimal electrode positioning over different portions of the quadriceps muscle to optimize more rational NMES clinical settings.