Eur J Appl Physiol (1995) 71:555-557
© Springer-Verlag 1995
S. F u k a s h i r o • M. I t o h • Y. Ichinose • Y. K a w a k a m i T. F u k u n a g a
Ultrasonography gives directly but noninvasively elastic characteristic of human tendon in vivo Accepted: 30 August 1995
Abstract. To obtain an insight into tendon elasticity during human movement, a real-time ultrasonography was applied to the contracting tibialis anterior muscle. The insertion point of fascicles onto the aponeurosis was clearly visualized, and its position relative to a fixed marker on the skin moved proximally (/11) according to the increasing dorsiflexion force ( / I F ) with a fixed ankle joint. Notably, t h e / i l - / i F relationship in the tendon was found to be quadratic in nature ( / I F = c/i1 2., c = 1 . 4 8 " 2 . 2 4 , r=0.985--0.992, n-9) as has been reported in the isolated tendon, although the A F - / I 1 curves were slightly underestimated in comparison with the stiffness constant estimated from tendon architecture. This underestimation might be caused by changes in the height of the foot arch with the application of force.
Key words: Human tendon elasticity • Ultrasonography • Tibialis anterior muscle • F-L curve
Introduction According to Hill's classical model, the skeletal muscletendon complex consists of contractile and series elastic components (CC and SEC, respectively). The SEC demonstrates elastic behavior in most movement patterns and especially when the muscle is activated and simultaneously stretched prior to concentric action (Komi 1984). Although the elastic characteristics of SEC can be observed through t h e / I F - / l l relation, direct measurement of this relation has been impossible. For this reason, these characteristics have been indirectly estimated by special in vivo and in vitro methods (e.g. Huijing 1992; Poussen, et al. 1990). Because the major part of the SEC is located in the tendinuous tissues of a muscle, we can consider some fundamental characteristics of the SEC with regard to tendon (Huijing 1992). The displacement at a certain point in the human tendon can be directly but noninvasively observed in vivo by using ultrasonography (Kawakami, et a1.1993). We can then obtain the delta lengthening of the tendon with the force by measuring the distance traveled by
a certain point on the tendon during an isometric contraction with increasing force. The purpose of this study was to determine the /1 F-/11 characteristics in a distal tendon of the human tibialis anterior muscle (TA) by ultrasonography.
Methods Subjects were 3 healthy male volunteers (24-31 yr of age, 172-178 cm in body height, 62-73kg in body weight). Informed consent was obtained from each subject before the study began. As shown in Fig. 1, the subject lay supine on a bed and was requested to perform isometric dorsiflexion with gradually increasing force in each trial at three ankle joint angles (90, 105 and 120 deg) by using a special ergometer (MYORET, ASICS, JPN). The ultrasonic image of the TA during contraction was recorded on a videotape synchronized with a clock timer to record time in ms and dorsiflexion torque. The lengthening of the distal tendon of the TA was estimated with ultrasonic apparatus. The ultrasonic apparatus (SSD-2000, ALOKA, JPN) consists of an electronic linear array probe of 7.5MHz wave frequency. The scanning head is coated with a water-soluble transmission gel, which provide acoustic contact without depressing the dermal surface. The transducer was placed perpendicular to the tissue interface and parallel to the tibia located at a point 50% distal in the tibial bone length. The tester visually confirmed the echoes reflected from the aponeurosis and interspaces between fascicles in the TA. Frame-by-frame photos of ultrasonic images recorded on video tape were printed every 25ms onto image recording paper. The lengthening of distal tendon (1) was calculated from the displacement of ' z/' between two consecutive images. After the ultrasonic probe was firmly positioned, a specially-designed placement marker (K) was set between the body and the probe so that K did not move, which was confirmed by VTR. The cross-point (r/) between two echoes; one echo from the deep aponeuroses and the other from fascicles, was easily determined on the ultrasonogram as shown in Fig.l. The echoes have been confirmed to be from the aponeuroses and fascicles through a comparison of ultrasonic measurements with direct measures on cadavers, with a measurement error < 10(Kawakami et al. 1993). Therefore, the displacement (7/) is considered to indicate the lengthening of the distal tendon. Conversely, the torque measured by the ergometer was converted to the force at the distal end of the tibialis anterior muscle, according to the moment arm of TA (Rugg et al. 1990).
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