Neuromuscular Activation Of Vastus Intermedius Muscle During Isometric Knee Extension At Various Force Intensities

Abstract

An investigation of the electromyography (EMG)-force relationship is one of the essential approaches to understand motor control in human skeletal muscle. For the quadriceps femoris (QF) muscle group, which plays an important role in human movement, EMG-force relationship is not fully understood, since it has been considered surface EMG can be recorded from only three superficial muscle components of QF muscle group. Recently, we reported the methodology recording the surface EMG from the remaining muscle component of the QF muscle group, the vastus intermedius (VI) muscle. Information about the activation of the VI muscle would be helpful to improve understanding of motor control of QF muscle group. PURPOSE: The purpose of our study is to compare the EMG-force relationship of the VI muscle with that of the other components of the QF muscle group in order to characterize neuromuscular activation of the VI muscle. METHODS: Thirteen healthy men performed maximal voluntary contraction (MVC) and submaximal contraction during isometric knee extension at 10% of the MVC to 90% of the MVC at intervals of 10% of the MVC level. Surface EMG was detected from four muscle components of the QF muscle group, i.e. VI, vastus lateralis (VL), vastus medialis and rectus femoris (RF) muscles. The electrode for the VI muscle was located at superficial region of this muscle defined by guidance of ultrasonography. Root mean squares (RMS) of EMG were calculated for each force level. RMS of submaximal contractions were normalized by the MVC. The difference between exerted force in the relative scale and normalized RMS were calculated at each force level and summed up for individual muscle components. RESULTS: Normalized RMS in the VI muscle was significant lower than in the VL muscle at a lower force level (20% and 40% of MVC, p < 0.05 each) and lower compared to the RF muscle at a higher force level (from 60% to 90% of MVC, p < 0.05 each). Sum of difference in EMG-force relationship of VI muscle from the identity line was significantly larger than RF muscle (p < 0.05). CONCLUSIONS: These results suggest that neuromuscular activation in the VI muscle is relatively lower than that of the other components of QF muscle group during submaximal knee extension contractions. In addition, the EMG-force relationship of the VI muscle negatively deviates from the identity line.