Neuromuscular Control of Rapid Linear Accelerations in Fish
Technical Report,01 Aug 2014,30 Apr 2015
TUFTS UNIV MEDFORD MA MEDFORD United States
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In this project, we measured muscle activity, body movements, and flow patterns during linear acceleration in the bluegill sunfish, Lepomis macrochirus. Animals with flexible bodies, like fishes, face a tradeoff for rapid movements. To produce high forces, they must make high amplitude movements of their fins, tails, or other propulsors, which requires that the propulsors be flexible to bend to high amplitude. However, the reaction forces from the environment are then large, which requires that the propulsors be stiff to resist these forces. Indeed, when we measured wake flow patterns, we found that the momentum flux was higher during acceleration, corresponding to high forces. Bluegill use their muscles to both produce power for rapid movements, but also to appear to use them to stiffen their bodies. During acceleration, but not during steady swimming, muscle tends to become active as it is being stretched, and muscle on the left and right side of the body are active simultaneously both of these effects should increase body stiffness. These results suggest that fish, and perhaps other soft-bodied organisms, can actively modulate the effective stiffness of their bodies in order to accelerate rapidly while also being able to swim efficiently.