Quantification of local surface strains of cat gastrocnemius medialis muscle during contraction

An in vivo method for measuring local deformations of the surface of skelet al muscles is presented. The method was applied to the aponeurosis of the m edial gastrocnemius muscle (MG) of cat. Approximately 150 fluorescent polys tyrene markers were attached to the aponeurosis and the distal muscle fibre s of the MG. Two-dimensional video recordings of the muscle-tendon complex in situ during active force production at fixed muscle length were made. Pr incipal strains (epsilon(1) and epsilon(2)) and strains in the longitudinal direction of the muscle-tendon complex (epsilon(lon)) and in the transvers e direction (epsilon(t)) were calculated. The aponeurosis extended during c ontraction of the MG. Mean longitudinal strain of the aponeurosis was appro ximately 2%. An increase in strain was found in the disto-proximal directio n. In the transverse direction, large inhomogeneities in the strain were fo und.