Energy-minimizing choices of muscles and patterns of movement.

Prilutsky (1999, target paper) reports that Crowninshield and Brand's (1981) criterion, minimization of the sum of the cubes of muscle stresses, works well as a predictor of the division of labor between muscles, for various tasks. However, no direct benefit from minimizing this particular sum is apparent, and it seems likely that it is merely a correlate of the criterion that actually drives muscle choice. In many tasks, there would be a clear, direct benefit from minimizing metabolic energy costs, as Prilutsky (1999) points out. Alexander (1997a, 1997b) and Minetti and Alexander (1997) have shown how the metabolic energy costs of muscle contraction can be estimated, and used to predict optimum muscle properties or optimal patterns of movement. This article explores the feasibility of using the same approach to predict optimum division of labor between one- and two-joint muscles.