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

An in vivo method for measuring local deformations of the surface of skeletal muscles is presented. The method was applied to the aponeurosis of the medial gastrocnemius muscle (MG) of cat. Approximately 150 fluorescent polystyrene markers were attached to the aponeurosis and the distal muscle fibres of the MG. Two-dimensional video recordings of the muscle-tendon complex in situ during active force production at fixed muscle length were made. Principal strains (ε1 and ε2) and strains in the longitudinal direction of the muscle-tendon complex (εlon) and in the transverse direction (εt) were calculated. The aponeurosis extended during contraction of the MG. Mean longitudinal strain of the aponeurosis was approximately 2%. An increase in strain was found in the disto-proximal direction. In the transverse direction, large inhomogeneities in the strain were found.