MECHANICAL-PROPERTIES OF APONEUROSIS AND TENDON OF THE CAT SOLEUS MUSCLE DURING WHOLE-MUSCLE ISOMETRIC CONTRACTIONS

Recent studies have suggested that the mechanical properties of aponeu rosis are not similar to the properties of external tendon. In the pre sent study, the lengths of aponeurosis, tendon, and muscle fascicles w ere recorded individually, using piezoelectric crystals attached to th e surface of each structure during isometric contractions in the cat s oleus muscle. We used a surgical microscope to observe the surface of the aponeurosis, which revealed a confounding effect on measures of ap oneurosis length due to sliding of a thin layer of epimysium over the proximal aponeurosis, After correcting for this artifact, the stiffnes s computed for aponeurosis was similar to tendon, with both increasing from around 8 F-0/L(c) (F-0 is maximum isometric force and L(c) is ti ssue length) at 0.1 F-0 to 30 F-0/L(c) at forces greater than 0.4 F-0. At low force levels only (0.1 F-0), aponeurotic stiffness increased s omewhat as fascicle length increased. There was a gradient in the thic kness of the aponeurosis along its length: its thickness was minimal a t the proximal end and maximal at the distal end, where it converged t o form the external tendon, This gradient in thickness appeared to mat ch the gradient in tension transmitted along this structure. We conclu de that the specific mechanical properties of aponeurosis are similar to those of tendon. (C) 1995 Wiley-Liss, Inc.