LENGTH-FORCE CHARACTERISTICS OF THE APONEUROSIS IN THE PASSIVE AND ACTIVE MUSCLE CONDITION AND IN THE ISOLATED CONDITION

Length behaviour of the entire and designated parts of the proximal ap oneurosis of the unipennate gastrocnemius medialis (GM) muscle of the rat was examined at muscle lengths ranging form muscle slack length to 4 mm above muscle optimum length in the passive and active (isometric contractions) muscle condition (n = 13). In addition, length-force ch aracteristics of the aponeurosis in the isolated condition were determ ined (n = 6). Going from muscle slack length to 4 mm above muscle opti mum length, the relative extension (relative to the length at muscle s lack length) yielded the following result. 14.3% for the entire aponeu rosis, 9.8% for the most proximal 25% of the aponeurosis, 3.5% for the middle 50% of the aponeurosis and 52.3% for the most distal 25% of th e aponeurosis. Aponeurosis length as a function of aponeurosis force w as significantly shorter in the active compared to the passive or isol ated condition for force values within the range of force encountered in all three conditions (0.3 1.0 N); no significant difference was obs erved between the passive or isolated condition. It is concluded that the extension of the aponeurosis is heterogeneously distributed along its length. Differences in aponeurosis length-force curves between the conditions may be explained in terms of a heterogeneous force distrib ution within the muscle.