Abstract: Objective To test the effect of different flexion angles of knee joint on the myoelectric activity and torque of quadriceps femoris and hamstring muscle when these muscles contracting.MethodsElectromyographic activities and isometric torque measurements were performed on 10 healthy subjects at 30°, 60° and 90° of knee joint flexion.ResultsThe results indicated that the greatest maximal voluntary isometric contracture-torque of quadriceps femoris occurred during knee extension at 60° of knee flexion ( P<0.01). However, no significant relationship of maximal voluntary isometric contracture-electromyography and maximal voluntary isometric contracture-torque of quadriceps femoris were found in 10 subjects. But when knee joint was at 90° flexion, hamstring muscle had a greatest neuro-myoelectric activity.ConclusionThe exercise of maximal voluntary isometric contraction of quadriceps femoris and hamstrings muscles at certain knee joint angle can help to maintain the stability of knee joint.

Key words: knee joint angle, agonistic muscle, antagonistic muscle, co-activation, surface electromyography