A linear description of shortening induced changes in isometric length-force characteristics of rat muscle

Active muscle shortening reduces the isometric force potential of muscle. This observation indicates that the isometric length-force characteristics are altered during muscle shortening. Post-shortening decrease in isometric force depends on starting length, shortening amplitude and shortening velocity. In the present study, post-shortening decrease in isometric force was determined after isokinetic contractions with various shortening amplitudes initiated from different lengths of rat medial gastrocnemius muscle. For a given target length post-shortening force decrease increased linearly with shortening amplitude. We found that the quotient of post-shortening force decrease and shortening amplitude depended linearly on muscle length. Based on our experimental results and those from other studies, we conclude that shortening induced changes in isometric length-force characteristics can be described by two simple functions. A linear function describing the influence of starting muscle length and shortening amplitude and an exponential function describing the influence of shortening velocity