The absolute value of the muscle efficiency and its decrease over time has vital consequences. Among other diseases, heart failure, which is the leading cause of death in developed countries, is dramatically affected by muscle weakness. This paper provides an analogy between the Carnot engine and muscle to gain insight on the muscle work production process and estimate the maximum muscle efficiency under physiological conditions. An ‘ideal muscle’ model, which operates steadily and reversibly, is defined and for this model energy and exergy analyses are performed. Theoretical results are compared with the experimental measurements.