LONG, JR, J.H.; ADCOCK, B.; ROOT, R.G.: Axial Tendons in Fish: How do Tensile Structures Create Beam-Like Behavior?

Recent work on the in vivo strain of red and white muscle has shown that the swimming fish body bends like a homogenous, continuous beam. This is surprising in light of the body�s heterogeneous tendon and connective tissue structure, myomere shape, and muscle activity. Our goal is to reconcile these two views. To do so, we mathematically model transitions within a structure between string- and beam-like mechanical behaviors. The model incorporates variation in flexural stiffness and tensile stresses caused by spatial and temporal variation in geometry and muscle activity. In this framework, tendons create beam-like behavior locally by limiting shear within the body. We tested these theoretical predictions with a computational model of a bending, jointed body. Our results suggest that undulatory swimming requires adaptive tuning of muscle activation to control the mechanical properties of the fish body as well as to generate bending moment.