The Cross-Bridge Spring: Can Cool Muscles Store Elastic Energy?

Abstract

Lock and Load in the Cold Muscle extensibility can act as an energy storage vehicle, like springs bouncing back after being compressed. George et al. (p. 1217 , published online 25 April) now show that energy can also be stored within muscles as a function of their natural temperature gradient. In hawkmoth muscle myofilaments, reduced cross-bridge cycling regionally constrains myofilaments, resulting in a "lock-spring lattice" that enables elastic energy storage as both the myofilaments and cross-bridges deform. Elastic energy stored in cross-bridges that remain bound and elastically deformed at the end of the first half of a contraction cycle can be released during the second half, thus serving as an additional elastic force. Such "bonus" energy may be especially important given the high energetic demands of flight, but because temperature gradients are a natural result of energy generation and heat dissipation in muscle, this mechanism could be more broadly important in locomotion systems.