Influence of Knee Joint Position on Co-contractions of Agonist and Antagonist Muscles during Maximal Voluntary Isometric Contractions: Electromyography and Cybex Measurement

Abstract

The purpose of this study was to investigate the influence of different angles of knee joint on the activation level of agonist and antagonist muscles from electromyographic activities and torque measurement during maximum isometric efforts. Electromyographic activities and isometric torque measurements were performed on 10 healthy subjects at 30, 60 and 90 of knee joint flexion with the hip fixed at 80 of flexion. To quantify the antagonist muscle activity, we normalized its electromyographic value at each joint angle with respect to its electromyographic value at the same angle acting as an agonist at maximal effort. The results indicate that the greatest maximal voluntary isometric contraction torque of the quadriceps occurred during knee extension at 60 of knee flexion. Co-activation of quadriceps and hamstrings at certain angles can help to maintain the stability of the knee joint. However, no significant relationship of maximal voluntary isometric contraction electromyography and maximal voluntary isometric contraction torque of quadriceps were found in our study. Further investigation of the torque and electromyographic relationship using combinations of different hip and knee angles are suggested.