Residual force enhancement in skeletal muscles: one sarcomere after the other.
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.
Departments of Kinesiology and Physical Education, Physics and Physiology, McGill University, Montreal, Canada. dilson.rassier@mcgill.ca
Dilson E
DE
Rassier
D001696:Biomechanical Phenomena; D006801:Humans; D018482:Muscle, Skeletal / Q000502:physiology*; D009210:Myofibrils / Q000502:physiology*; D012518:Sarcomeres / Q000502:physiology*