Fig. 11

Directly measured cat medial gastrocnemius force as a function of the directly measured length of the corresponding lateral aponeuroses. Forces were measured using a standard buckle type force transducer [48, 52,53,54,55,56,57,58,59] and aponeurosis lengths were measured using two sonomicrometry crystals aligned along the mid-longitudinal collagen fascicles of the aponeurosis [83]. Note the counter-clockwise orientation of these “force-elongation” curves, and note the similar elongations of the aponeurosis in the passive muscle during the swing phase of locomotion (forces below about 10 N) and the active muscle during the stance phase of locomotion (forces between about 10 and 100 N). These direct force and elongation measurements indicate that there is no relationship between force and the elongation of the lateral aponeuroses, therefore the aponeuroses length is NOT an indicator of muscle force and is not in series with the muscle force (tendon). Furthermore, if we interpreted that the aponeurosis shown here is in series with the muscle’s contractile element or its tendon, we would obtain net work from an elastic element, an impossibility