Integrated actions of the four heads of quadriceps femoris: An electromyographic study

Abstract From intramuscular bipolar fine‐wire electrodes in the four heads of quadriceps femoris, electromyographic recordings were made (along with electrogoniometric records) in nine normal men and women during selected postures and movements of the loaded and unloaded knee. Variation between the onset and cessation of activity between the four heads and from subject to subject was found, but the vastus medialis reflected the general pattern of activity rather than acting only terminally during extension. Rectus femoris had the shortest span of activity during extension of the knee.