Functionality of disorder in muscle mechanics

TL;DR

This paper explores how the collective bistable behavior of muscle components enables rapid force adaptation and reveals a double-criticality due to filament disregistry, which may be functionally advantageous.

Contribution

It introduces a model showing that filament disregistry places muscle units near two critical points, enhancing robustness and functionality.

Findings

Muscle force response involves collective bistable elements.

Disregistry positions units near two critical points.

Double-criticality enhances muscle robustness.

Abstract

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.