Muscular force production during non-isometric contractions: Towards numerical muscle modeling

Abstract: The main objective of the study was to investigate skeletal muscle force production during isometric contractions, active muscle stretches and shortenings. The motivation behind this work is to improve the dominant model of muscle contraction force generation based on the theories of Hill. The effect of force modification was observed after concentric and eccentric contractions and also stretch-shortening cycles. It has been shown that this force modification is not related to lengthening/shortening velocity, and the steady-state force after non-isometric contractions can be well described by initial isometric force and mechanical work performed by and on the muscle during length variations. The time constants calculated for isometric force redevelopment appeared to be in certain relations with those for initial isometric force development, an observation which extended our basis for ongoing muscle modeling. The main method of the project consists in two extensive series of experiments on mouse skeletal muscles. Analysis of the first series of experiments, concentric contractions, with an emphasis on the force depression has been presented in Paper 1. Paper 2 is based on contractions with various stretches and shortenings as well as their combination, force modification and its predictor are the quantities of interest. The third part of the project is also based on the second series of experiments. Timing aspects of the force production were calculated there.