ABSTRACT
This study was prompted by reports of resting tension in muscles of various arthropods (Machin & Pringle, 1959; Hoyle, 1968; Burns & Usherwood, 1978; Hoyle, 1978; Hawkins & Bruner, 1979) and our observation that when the legs of the cockroach and crab are severed from the thorax, the joints appear to assume rather fixed angles. Recently Chesler & Fourtner (1981) have shown that significant resting tension exists in one of the femoral extensors of the cockroach (muscle 177 d) (Carbonell, 1947). The purpose of this study was to determine if resting tension is characteristic of all the limb muscles and if it could account for the fixed angle of the joint. We present evidence in this report that resting tension in the leg muscles of the cockroach, Periplaneta americana, and the crab, Carcinus maenas, is responsible for maintaining a relatively fixed angle in the joints of the limbs. These data, along with other evidence, provide a good argument for a system in which posture is partially maintained in these arthropods by resting tension which appears to be passive in nature. The maintenance of posture by this passive mechanism could result in an energetic savings in a quiescent arthropod.
