Huijing P A, Baan G C, Rebel G T
Instituut voor Fundamentele, Faculteit Bewegingswetenschappen, Vrije Universiteit, Amsterdam, The Netherlands.
J Exp Biol. 1998 Mar;201(Pt 5):683-91.
The extensor digitorum longus muscle (EDL) of the rat hindleg consists of four heads. The heads are named after their insertions on the digits of toes II, III, IV and V. The EDL heads share a proximal tendon and aponeurosis, but have separate distal aponeuroses and tendons. By cutting the distal tendons of selected heads, direct myotendinous force transmission within these heads is prevented. Therefore, force exerted by the muscle would be expected to decrease according to the physiological cross-sectional area disconnected if myotendinous force transmission were the only mechanism of force transmission. The results indicate that EDL force production remained at high levels after acute tenotomy: muscle length-force curves did not alter significantly following cutting of the tendons of heads II and III. Cutting the tendon of head IV as well leaves only head V in its original condition. After tenotomy of head IV, length-force characteristics were altered significantly, but optimum force was maintained at 84% of that of the intact muscle. After separation of head IV from head V intramuscularly for some distance along their interface, the force dropped to much lower levels, with optimum force approaching 50% of that of the intact muscle. The length of active proximal fibres (located within head II) did not remain constant but increased with increasing muscle lengths after tenotomy as well as after partial separation of heads IV and V. The amount of length change decreased after intramuscular separation of the heads, indicating declining reactive forces. It is concluded that force transmission occurred from tenotomized heads to their intact neighbours and vice versa. The magnitude of the force transmitted from head to head was dependent on the degree of integrity of the connective tissue at the interface between heads.
大鼠后肢的趾长伸肌（EDL）由四个头组成。这些头根据其在第二、三、四和五趾上的附着点命名。EDL的头共享一个近端肌腱和腱膜，但有独立的远端腱膜和肌腱。通过切断选定头的远端肌腱，可以防止这些头内的直接肌-腱力传递。因此，如果肌-腱力传递是唯一的力传递机制，那么根据断开的生理横截面积，肌肉施加的力预计会降低。结果表明，急性切断肌腱后，EDL的力产生仍保持在较高水平：切断第二和三头的肌腱后，肌肉长度-力曲线没有显著改变。再切断第四头的肌腱后，只剩下第五头保持原状。切断第四头的肌腱后，长度-力特性发生了显著改变，但最佳力保持在完整肌肉的84%。在第四头和第五头沿着它们的界面在肌肉内分离一段距离后，力下降到低得多的水平，最佳力接近完整肌肉的50%。活跃近端纤维（位于第二头内）的长度在切断肌腱后以及第四头和第五头部分分离后，并不保持恒定，而是随着肌肉长度的增加而增加。头部分离后长度变化的量减少，表明反作用力下降。得出的结论是，力从切断的头传递到其完整的相邻头，反之亦然。从一个头传递到另一个头的力的大小取决于头之间界面处结缔组织的完整程度。
