  A salient feature of skeletal muscles is their ability to take up an applied
slack in a microsecond timescale. Behind this remarkably fast adaptation is a
collective folding in a bundle of elastically interacting bistable elements.
Since this interaction has long-range character, the behavior of the system in
force and length controlled ensembles is different; in particular, it can have
two distinct order-disorder--type critical points. We show that the account of
the disregistry between myosin and actin filaments places the elementary
force-producing units of skeletal muscles close to both such critical points.
The ensuing "double-criticality" contributes to the system's ability to perform
robustly and suggests that the disregistry is functional.
