IIT Professor of Biology and Physics Thomas Irving, with co-authors Tom Daniel and Nicole George of University of Washington and C David Williams of Harvard University, this week published “The Cross-Bridge Spring: Can Cool Muscles Store Elastic Energy?” in Science.

Abstract
Muscles not only generate force. They may act as springs, providing energy storage to drive locomotion. Although extensible myofilaments are implicated as sites of energy storage, we show that intramuscular temperature gradients may enable molecular motors (cross-bridges) to store elastic strain energy. Using time-resolved small-angle x-ray diffraction paired with in situ measurements of mechanical energy exchange in flight muscle of Manduca sexta, we produced high-speed movies of x-ray equatorial reflections, indicating cross-bridge association with myofilaments. A temperature gradient within the flight muscle leads to lower cross-bridge cycling in the cooler regions. Those cross-bridges could elastically return energy at the extrema of muscle lengthening and shortening, helping drive cyclic wing motions. These results suggest that cross-bridges can perform functions other than contraction, acting as molecular links for elastic energy storage.