STRAIN DISTRIBUTION ON RAT MEDIAL GASTROCNEMIUS (MG) DURING PASSIVE STRETCH

Deformation oi the surface of passive medial gastrocnemius muscle (MG) was measured in vivo while performing a hysteresis test. The gastrocn emius muscle of male rats were dissected free and the distal tendon wa s cut. The lateral head was separated from the medial head. The muscle origins were left intact. 60-70 fluorescent, polystyrene spheres (dia meter 0.7 mm were attached to the surface of the MG. During the experi ment. two-dimensional video recordings of the movements of the MG were made. The coordinates of the marker centroids were obtained by comput er processing of digitized images and marker displacements as a functi on of time were calculated. Green Lagrange strains in two principal di rections were calculated (epsilon(1), epsilon(2)) for three specimens, epsilon(1) had approximately the same direction as the muscle fibers. The longitudinal strain of the fibers (20 30%) was larger than the st rain of the aponeurosis (1-5%); p < 0.001. No significant difference w as found between the values of the transverse strains of muscle fibers and aponeurosis; the value of epsilon(2) was -6 to -9% for both tissu e structures. Copyright (C) 1996 Elsevier Science Ltd.