Coordination of one- and two-joint muscles during voluntary movement: theoretical and experimental considerations.

The target article by Dr. Prilutsky is based on three incorrectly derived mathematical rules concerning force-sharing among synergistic muscles associated with a cost function that minimizes the sum of the cubed muscle stresses. Since these derived rules govern all aspects of Dr. Prilutsky's discussion and conclusion and form the basis for his proposed theory of coordination between one-and two-joint muscles, most of what is said in the target article is confusing or misleading at best or factually wrong at worst. The aim of our commentary is to sort right from wrong in Dr. Prilutsky's article within space limitations that do not allow for detailed descriptions of mathematical proofs and explicit discussions of the relevant experimental literature.