The stiffness of parallel elastic elements in rat papillary muscle

Summary The dynamic stress-strain relationship of the parallel elastic element (PE) in rat papillary muscle has been investigated.This relationship cannot be correctly estimated by means of the classical diagram: muscle length-stable passive tension of the whole muscle. A new experimental approach has been developed by which the elastic properties of PE may be measured under dynamic conditions.After isometric stabilization of the muscle at a series of preloads, tension changes following quick release were measured. The tension-length relationships measured under these conditions were used to evaluate the elastic behaviour of the parallel elements.The results obtained show that the stiffness of PE is higher than expected and that its maximum elongation never exceeds 10% of the respectiveL_o value at all preload levels explored.Preliminary communication at: International Congress of Physiological Sciences, Munich, July 1971. This study was partially supported by a grant from the Consiglio Nazionale delle Ricerche (CNR, Rome, Italy).