In today’s Academic Minute, Dr. C. David Williams of Harvard University explains how our bodies store and release energy as we move.
David Williams is a postdoctoral researcher in the Department of Organismic and Evolutionary Biology at Harvard University. His work in the Biewener Lab at the Concord Field Station is focused on understanding the control of biological motion, scaling from the molecular dynamics of individual motor molecules to the kinematics of animal movement.
Dr. C. David Williams – Muscles and Energy Storage
Muscle is a highly structured system. Tiny tissue pieces contain millions of individual motors that generate force. These motor molecules don’t have a forward and reverse gear, and aren’t even all that great at pulling in a straight line. The structure around the motors has to coerce them into working together, pulling in the same direction at the same time, without concentrating too much force at any one point and ripping the system apart. For a long time, we thought this support structure was pretty much just there to keep muscle organized.
But there is another great driving factor in movement, and that is the desire for efficiency. We don’t want to spend more energy than necessary to do something, so we like to store energy and reuse it when we can. We do this when running, storing energy in the tendons and ligaments of our legs. We also can use stored energy to perform actions we couldn’t even make happen otherwise. We can throw farther thanks to being able to store energy in the elastic components of our shoulders and chests. And it’s not just us, for example Mantis shrimp, animals that look like deranged crawfish, use energy stored in their exoskeletons to move their claws at a blinding speed and wallop open the shells of their prey.
So we’ve thought we had the functions of systems figured out: energy is stored in tendons, ligaments, connective tissue, and even exoskeletons, while force is generated in muscle. But it turns out that we missed something: muscle serves a dual function; it is storing energy whilst generating force.
The structure that organizes muscle’s motors deforms under force and, in doing so, it stores energy. Muscle's support structure deforms and stores energy not only in the direction of force, but also perpendicular to it, in the direction that muscle bulges as it contracts. So muscle isn’t just a motor that produces force and consumes energy, it is also a rubber band that lets us bounce along on less energy than would otherwise be the case.