Meeting Abstract
Fluid filled cylinders reinforced by stiff fibers (commonly referred to as helically-wound hydrostats) are ubiquitous in biological systems. Functionally, they have been shown to provide locomotor and postural support to organisms, to prevent buckling during bending, and to prevent high internal pressures from causing nonuniform bulging. Their consistent biomechanical relevancy has led to the general hypothesis that when a new helically wound hydrostat is discovered, an accompanying biomechanical role for it will not be far behind. Individual vertebrate skeletal muscles have all the components of a typical helically wound hydrostat, but the possibility of a hydrostatic interaction present within them has not been widely explored. In the present study we investigate the hydrostatic nature of individual skeletal muscles by comparing the passive mechanical properties of bullfrog semimembranosus muscles to those of a simple physical model. The model comprises a fluid filled balloon enclosed in a helically wound sheath of plastic fibers, and represents a single muscle fascicle wrapped in perimysial connective tissue. We find that in response to stretch our physical model qualitatively mimics the length-tension and length-pressure characteristics of passively stretched muscles. We suggest that a hydrostatic interaction may control the passive behavior of skeletal muscles at relatively long muscle lengths, and that the rise in intramuscular fluid pressure that accompanies extreme muscle stretching may be an indicator of collagen’s contribution to passive tension. Supported by NIH grant AR055295.
