History dependence of force production in skeletal muscle: a proposal for mechanisms.

Force production in skeletal muscle is history-dependent. This observation has been made numerous times in the past fifty years and the idea of history-dependent properties has been accepted in the scientific community. Nevertheless, history-dependent properties are largely neglected in theoretical models of skeletal muscles, and the mechanism responsible for these properties is not known. Here, a mechanism is proposed to explain the long-lasting, isometric force depression following muscle shortening and some of the experimental evidence in support of this mechanism is presented. Some thoughts (albeit not a mechanism) are also provided on possible explanations for the long-lasting, isometric force enhancement following muscle stretching. It is hoped that the considerations made here might stimulate a renewed interest in an old but unresolved topic in muscle mechanics.