Abstract des Autors

This study was designed to examine function of the vastus lateralis muscle (VL) fibers during maximal voluntary contraction (MVC) in knee extension which was exerted based solely on the kinesthesia acquired from repeating the MVC movements. Fifteen men performed 10 consecutive isokinetic knee extensions comprising 7 passive contractions and 3 MVCs, which was repeated for 7 sets. In the first 3 sets, subjects were instructed to perform MVCs immediately a light cue appeared when the leg reached 60 deg knee joint angle in the 3rd, 6th, and 9th extensions; in the next 4 sets, subjects tried to maintain the timing of MVC repetitions without the light cue. VL electromyographic activity was monitored. The point where a fascicle arose from the deep aponeurosis and the pennation angle were measured on VL ultrasonic images. Subjects classified their MVC performance (force and timing) into 5 grades after each set. Based solely on kinesthesia (without the light cue), the VL fibers contracted tightly to a point where the fascicle arises from the deep aponeurosis, and it appeared to compensate for a delay in reaction time to start MVC. However, the subject’s self-evaluation remained unchanged despite the changes in muscle behavior during MVC. In the 4th set only, when the light cue was not used for the first time, did their self-evaluation tend to decrease and VL pre-activity was significantly increased. These results suggest that kinesthesia does not always correspond to actual muscle activity.