Fig. 1. Schematic illustration of force enhancement following stretch according to
the sarcomere-length non-uniformity theory. A muscle is stretched on the
descending limb of the force—length relationship from an initial average
sarcomere length (open circle) to a final average sarcomere length (filled
square). During stretching of the muscle, it is assumed that some sarcomeres
are stretched less than average (filled circle, left) while others are
stretched more than average (filled circle, right). The sarcomeres that are
stretched less than average are stronger than an average sarcomere would be,
because of the slope of the force length relationship. The sarcomeres that are
stretched more than average become weaker initially, but then are `caught' by
the passive force of the muscle, and they elongate until a force equilibrium
is established between the short and long sarcomeres. This force at
equilibrium (dashed line) is greater than the expected force at the average
sarcomere length, and therefore, this mechanism can potentially account for
the observed force enhancement following muscle stretch.
