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Ultrasonography, exploration of human muscle‐tendon function

In the present issue Dr Kubo et al. from The Department of Life Sciences in Tokyo have collected data using ultrasonography that suggest that the passive properties of in vivo tendon structures of the human medial gastrocnemius are considerably compliant. While these findings may seem intuitive, it is nevertheless an advancement of our current knowledge of human in vivo physiology, since similar observations have previously been limited to animal and cadaver research, which may not necessarily represent human in vivo conditions. Tendon mechanical properties play an important role in the function of the entire muscle-tendon complex: human movement comes about from the force exerted by contracting muscle, which is subsequently transmitted to bone via the extensible aponeurosis and tendon. While the structure and function of the muscle cell has received a certain attention, considerably less is known about that of the tendon and aponeurosis. Our current understanding of tendon behavior is largely based on experimental animal or cadaver data from mechanical testing of tendon specimens. Therefore, the techniques employed by Dr Kubo and coworkers, which is based on the use of ultrasonography during isometric muscle contractions, can be very useful for studying human tendon behavior in vivo non-invasively. The technique was developed in the mid 90 s (Fukashiro et al. 1995) and numerous reports have since been published. However, it should be noted that although the technique is very attractive, several issues still deserve careful considerations. (1) Since the technique is based on the displacement of intramuscular fascicular structures that can be observed on the ultrasound image, the resulting deformation does not represent that of the tendon per se, but rather the total deformation of the combined tendon and aponeurosis distal to the measurement site. (2) The method accounts for only two dimensions of structural deformation (i.e., in the sagital plane),