Meeting Abstract
The geometry of the musculoskeletal system, such as moment arms and linkages, determines the link between muscular functions and external mechanical results but as the geometry becomes more complex, this link becomes less clear. The musculoskeletal system of snakes is extremely complex, with several muscles which span numerous vertebrae, ranging from 10 to 45 vertebrae in the snake semispinalis-spinal (SSP) muscles (a dorsiflexor). Furthermore, this span correlates with habitat, with burrowing and aquatic species showing short spans while arboreal species show longer spans. Similar multi-articular spans are present in the prehensile tails of primates, the necks of birds, and our own digits. However, no previous analysis has adequately explained the mechanics of these multi-articular spans, either relative to mono-articular configurations or compared to greater or lesser spans. This talk uses well-established analysis techniques including the Method of Sections and the Minimum total potential energy principle to analyze the consequences of multiarticular muscle configurations. I show that multi-articular systems require a fundamentally metameric structure in which N joints require N muscles, as unconstrained internal degrees of freedom allow the system access lower potential energy states by sagging or buckling. For a cantilevered snake, increasing multi-articular span reduces both the force needed from any given muscle and the total muscular force needed across the entire muscular system. However, this improvement follows a hyperbolic distribution, with the greatest gains in transitions from mono-articular to spans of 2 or 3; all known snake SSP lengths fall into a region of much lower force with nearly linear slope and diminishing returns for extreme lengths. Continued work will examine dynamic locomotion and potential tradeoffs.
