Muscle architecture and control demands.

Muscles effect locomotion, and their gross architecture still poses analytical problems. These problems involve the arrangement of myofibers and motor units within muscles and that of muscles around joints. The arrangement of fibers may involve a range of considerations from the equivalence or nonequivalence of sarcomeres to placement, attachment, and angulation of fascicles and entire muscles; consequently, these levels and their development and coordination overlap. Many problems at the macroscopic level require clarification of how an animal uses a compartment of suite of muscles and whether morphological differences reflect functional ones. The understanding of intermediate architecture, including issues of compartmentation, pinnation, and concatenation, remains more elusive, as some morphologically distinct muscles may be functionally equivalent. As yet we have inadequate appreciation of the opportunities or limitations provided to the control system by a particular arrangement of fibers, or vice versa. Exploration of the rules that govern these conditions provides abundant opportunities for cooperation among neurobiologists, developmental biologists, physiologists and morphologists.