A dynamometer for nature's engines

Muscle is an amazing natural thermodynamic engine that converts chemical energy into mechanical work. Each muscle twitch is `sparked' by an electrically-released pulse of calcium ions, which trigger force-development and cell shortening, at the cost of energy and oxygen, and the dissipation of heat. Like other engines, muscle is inefficient at converting chemical energy to mechanical energy; at least 80% of the energy consumed by the muscle is released as heat. When we want to measure or enhance the performance of a human-made engine, such as an internal combustion engine, we typically attach it to a dynamometer-a device that can apply a controlled load to the engine, and measure its fuel consumption and work output. Imagine that we had a similar tool that allowed us to inspect nature's engine-muscle tissue-and thereby measure its energetic performance. Such a tool would allow us to better understand the muscle's work output and energy consumption, diagnose problems with the engine, tune its performance, and observe its response to changes in load, or to additives in its fuel. In this article, we report on our construction of a dynamometer for heart muscle.