Meeting Abstract
Musculoskeletal mechanisms yield output motion and force transmission determined by the configuration of anatomical components and the dynamics of muscle contraction. Computational models of these systems can help us to understand how morphology maps to function at different levels. How do we test for functional convergence in biomechanics? How do we define functional characters and determine when they are similar or equivalent? This study expands previous lever and linkage modeling, with software for more complete path analysis of linkage motion and simulation of structure-function relationships in a wide range of mechanisms, both simple and complex. Levers are often characterized as having one-to-one mapping, yet by incorporating muscle we find that simple levers are conclusively one-to-many. Four-bar linkages have been claimed to yield many-to-one (convergent) mapping, whereas simulations show that structural changes in four-bar linkages map to unique sets of primary functional variables (vector direction and magnitude of motion) so that linkages are in fact one-to-one. However, similar to levers, the dynamic role of muscle in powering linkages gives every individual linkage system a one-to-many capacity. Examples from cranial systems show that some biomechanical traits diverge and evolve due to linkage changes, and others in which muscle morphology is modified but linkages remain static. A protocol for defining convergent and divergent functional characters is proposed. Computational linkage modeling helps us to conclude that the geometry and physiology of muscles are critical to accurate estimations of lever and linkage function, that a more detailed path analysis of mechanical behavior helps to avoid some pitfalls of linkage comparison, and that multiple mechanical variables and levels of design should be considered when defining convergent or equivalent biomechanical systems.
