Skeletal muscle architecture: implications for muscle function and surgical tendon transfer.

Skeletal muscles have mechanical properties that are well-described by the length-tension relationship (for isometric contractions) and the force-velocity relationship (for isotonic contractions). These two intrinsic properties are scaled for a given muscle based on its architectural properties. Muscle active force-generating range is determined by muscle fiber length, while maximum muscle force is determined by physiologic cross-sectional area. These and other architectural properties should be matched between muscles when planning surgical tendon transfers in order to closely match donor and recipient muscles. Finally, the fiber length/moment arm ratio of a muscle-joint combination must be considered when describing strength because strength is a manifestation of both muscle and joint properties and not either alone. Unfortunately, detailed description of normal musculoskeletal design or optimal transfer strategy cannot be made until more basic science studies of the musculoskeletal system are conducted.