[MUSCLES MAY MOVE NOT ONLY TO THE LONGITUDINAL DIRECTION BUT ALSO TO THE LATERAL DIRECTION ----- A NEW PRINCIPLE DEVELOPED FROM THE OPENING ACTIVITY OF THE URETHRA ----].

(Purpose) Muscles shrink and stretch in the longitudinal direction along the running axis of muscle fibers. The "bi-metal", a widely utilized industrial instrument, is a device composing two metal plates pasted together. Since the coefficient of thermal expansion of the two metal plates differ from one another, the device bends in the lateral direction by heating. In the case of muscles, it may be possible to bend in the lateral direction, if the adjoining neighbor contracting units within them are adequately pasted together and contract to slightly different extents. We named this presumed movement as the "lateral creeping" of muscles. (Object and method) As an example, the movement of the abdominal rectus muscles was analyzed by a newly proposed biomechanical model for the "lateral creeping". (Results) It has been proved that the rectus muscle moves according to the pattern of the "lateral creeping", anatomically, mechanically and electromyographically. (Conclusion) There is a possibility that all the muscles may move as the "lateral creeping". Although this effect of muscles has not been considered in conventional physiology, if it is possible, the analysis of complicated movements in various muscles in the body, --- such as cardiac, lingual, or sphincter muscles ---, might be feasible in a simple way.