Friedrich Schiller University, Institute of Sport Science, Motion Science, Seidelstraße 20, 07749 Jena, Germany.
J Exp Biol. 2012 Feb 15;215(Pt 4):578-83. doi: 10.1242/jeb.054585.
Unlike most other arthropods, spiders have no extensor muscles in major leg joints. Therefore, hydraulic pressure generated in the prosoma provides leg extension. For decades, this mechanism was held responsible for the generation of the majority of the ground reaction forces, particularly in the hind legs. During propulsion, the front leg pairs must shorten whereas the hind legs have to be extended. Assuming that hind legs are essentially driven by hydraulics, their force vectors must pass the leg joints ventrally. However, at least in accelerated escape manoeuvres, we show here for the large cursorial spider species Ancylometes concolor that these force vectors, when projected into the leg plane, pass all leg joints dorsally. This indicates a reduced impact of the hydraulic mechanism on the generation of ground reaction forces. Although hydraulic leg extension still modulates their direction, the observed steep force vectors at the hind legs indicate a strong activity of flexors in the proximal joint complex that push the legs against the substrate. Consequently, the muscular mechanisms are dominant at least in the hind legs of large spiders.
与大多数其他节肢动物不同，蜘蛛的主要腿部关节没有伸肌。因此，在体腔中产生的液压为腿部伸展提供动力。几十年来，这种机制被认为是产生大多数地面反作用力的原因，特别是在后腿。在推进过程中，前腿必须缩短，而后腿必须伸展。假设后腿主要由液压驱动，它们的力矢量必须通过腿部关节的腹侧。然而，我们在这里至少在加速逃逸运动中展示了对于大型奔跑蜘蛛Ancylometes concolor 来说，当这些力矢量被投射到腿部平面中时，它们都通过腿部关节的背侧。这表明液压机制对地面反作用力的产生的影响较小。尽管液压腿部伸展仍然可以调节它们的方向，但在后腿上观察到的陡峭力矢量表明，在近端关节复合体中，屈肌的活动很强，将腿部推向基质。因此，肌肉机制至少在大型蜘蛛的后腿中占主导地位。
