A variety of systems to drive cardiac assist devices with power from skeletal muscle have been proposed and are under development. The power available from a fixed mass of muscle is metabolically limited and maximizing sustained power is required for the successful application of such devices. The purpose of this study is to develop an approach that can yield relative metabolic utilization measures from single contractions of whole muscle used for cardiac assistance. Similar to classical muscle energetic studies, myothermic methods were employed in which muscle temperature was measured with a fast responding thermister and an infrared radiation thremopile transducer. In a series of tests on rabbit soleus muscle, the relative temperature increases during contractions were recorded. Relative muscle temperature increase was linearly related to the contraction duration. This relationship was incorporated into an existing muscle model to predict the optimum parameters for sustained skeletal muscle power generation.