ELECTROMYOGRAPHIC STUDY OF THE FUNCTION OF M. RECTUS FEMORIS

The rectos femoris is a two joint muscle, and it is well known as a flexor of the hip joint and extensor of the knee joint. Especially, it is acknowledged by many anatomists and kinesiologists that the muscle is a prime mover as a knee extensor. Since a few years ago; we have recorded the electromyograms of the rectos femoris on various movements involving knee extension - the leg extension movements of the bicycle, the boat, the jump, the kick, and so on. Although knee extension was actively performed in these movements, we occasionally found some cases in which no action potentials were recorded from the rectos femoris. The Electromyographic studies of the fundamental movements which dealt with the rectus femoris have been made by several investigators - Wheatley & Jahnke, Basmajian, McCloy, Tsuyama & Suzuki and Takagi. But, as far as we know, no detailed study has been made on the difference of the discharge patterns of the rectos femoris during knee extension. McCloy reported in his study that when the leg was raised forward with strong extension of the knee, large action potentials were recorded from the rectos femoris, but when the thigh was raised backward with strong straightening of the knee, there was almost no evidence of contraction of the rectos femoris. However, he did not mention the reason why the difference appeared. Thus, the rectos femoris is, in effect, a two joint muscle, and it is understood from a study of the anatomical position of the muscle that the contraction of these fibers causes hip flexion as well as knee extension. Therefore, we can assume that the function of the muscle will be strongly affected during knee extension with the hip flexed or extended and actively stabilized or not stabilized. On the other hand, the difference of the discharges may be influenced by the direction of the movement in the opposite knee, as is known as reciprocal innervation. Thus, we made the subject perform knee extension taking various postures of the hip and making the opposite knee move to the direction of flexion or extension. We recorded the electromyograms from the rectos femoris during those movements and analyzed anatomically and mechanically.