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Abstract
A muscle fiber was modeled as a series-connected string of sarcomeres, using an A.
V. Hill type model for each sarcomere and allowing for some random variation in the
properties of the sarcomeres. Applying stretches to this model led to the prediction
that lengthening of active muscle on or beyond the plateau of the length tension curve
will take place very nonuniformly, essentially by rapid, uncontrolled elongation of
individual sarcomeres, one at a time, in order from the weakest toward the strongest.
Such a "popped" sarcomere, at least in a single fiber, will be stretched to a length
where there is no overlap between thick and thin filaments, and the tension is borne
by passive components. This prediction allows modeling of many results that have previously
been inexplicable, notably the permanent extra tension after stretch on the descending
limb of the length tension curve, and the continued rise of tension during a continued
stretch.