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Abstract
History-dependence is a well accepted property of skeletal muscle. Following active stretching, the steady-state muscle force is increased, and following active shortening, it is depressed compared to the force produced for the purely isometric contraction at the corresponding length. Despite much work in this area of skeletal muscle biomechanics many questions remained unanswered. Therefore, the purpose of this thesis was to systematically investigate the effect of history-dependence in whole skeletal muscle on the descending limb of the force-length relationship.
Steady-state forces following active stretching were greater than the isometric forces at the initial (and therefore the final) muscle length, and were smaller following active shortening than the isometric forces at the corresponding muscle length. Force enhancement and force depression increased with increasing amounts of stretching and shortening, respectively. Force enhancement increased with increasing final muscle length, whereas force depression increased with decreasing final muscle length. Novel to the literature was the observation that force enhancement exceeded the maximal isometric forces at the optimal muscle length for some stretch conditions, and was associated with a contribution from a passive component.
