TENDINOUS MOVEMENT OF A HUMAN MUSCLE DURING VOLUNTARY CONTRACTIONS DETERMINED BY REAL-TIME ULTRASONOGRAPHY

The degree of shortening or lengthening of muscles during joint action s has not been clarified in humans, although such information is essen tial in understanding human muscle functions. In this study, the tendi nous movement of a muscle was determined by real-time ultrasonography during voluntary contractions. The tibialis anterior muscle (TA) was t ested in five healthy men who performed dorsi- and plantar flexion mov ements (shortening and lengthening of TA) at two frequencies (0.1 and 1.5 Hz). The insertion point (eta) of fascicles onto the aponeurosis w as clearly visualized on the ultrasonogram, and its position relative to a fixed marker moved proximally and distally according to dorsi- an d plantar flexion of ankle joint. The movement of eta occurred in phas e with the angular change of ankle joint, giving high correlations (I = 0.93 to 0.97) between the displacement of eta and the angle. The dis placement of eta for one radian of joint angle change, 46.5 +/- 1.7 (S D) mm, was comparable to the reported moment arm of TA. The present me thod has many potential applications in the field of muscle physiology and biomechanics in humans.