Influence of Muscle Length on the Mechanical Parameters of Myocardial Contraction

Abstract Stiffness determinations were made on rabbit papillary muscles at different lengths. Both in resting preparations and in muscles contracting at lengths, where resting force was very low compared with active force, the stiffness increased recti‐linearly with force. At any force level, the stiffness of a preparation was greater at rest than during activity.—Force‐velocity curves were determined at different muscle lengths and, when necessary, data for the whole preparation were corrected for the influence of the parallel elasticity in order to derive the force‐velocity curves of the contractile element alone. V max and P O of the contractile element ( i.e . its shortening velocity at zero load and its maximum force‐producing capacity) determined at peak isometric force were increased approximately in parallel by elongation at short muscle lengths, whereas at lengths near the optimum for active force, V max was influenced slightly more than P o by length changes.—The time course of the active state was critically dependent upon muscle length: an increase in length prolonged the time from stimulation to 60% decay of the active state, without significantly altering the time course of its rising phase.