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J Muscle Res Cell Motil. 2012 Aug;33(3-4):155-65. doi: 10.1007/s10974-012-9308-7. Epub 2012 Jun 23.

Residual force enhancement in skeletal muscles: one sarcomere after the other.

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Departments of Kinesiology and Physical Education, Physics and Physiology, McGill University, Montreal, Canada.


The force-length relation is one of the most prominent features of striated muscles, and predicts that the force produced by a fully activated muscle is proportional to the overlap between myosin and actin filaments within sarcomeres. However, there are situations in which the force-length relation deviates from predictions based purely on filament overlap. Notably, stretch of activated skeletal muscles induces a long-lasting increase in force, which is larger than the force produced during isometric contractions at a similar length. The mechanism behind this residual force enhancement and deviations from the original force-length relation are unknown, generating heated debate in the literature. We performed a series of experiments with short segments of myofibrils and isolated sarcomeres to investigating the mechanisms of the residual force enhancement and the force length-relation. In this paper, evidence will be presented showing that force enhancement is caused by: (i) half-sarcomere non-uniformities, and (ii) a sarcomeric component, which may be associated with Ca(2+)-induced stiffness of titin molecules. These mechanisms have large implications for understanding the basic mechanisms of muscle contraction.

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