Red muscle activity in bluegill sunfishLepomis macrochirusduring forward accelerations

Abstract

27Fishes generate force to swim by activating muscles on either side of their flexible bodies. To 28 accelerate, they must produce higher muscle forces, which leads to higher reaction forces back 29 on their bodies from the environment. If their bodies are too flexible, the forces during 30 acceleration cannot be transmitted effectively to the environment. Here, we investigate whether 31 fish can use their red muscle to stiffen their bodies during acceleration. We used high-speed 32 video, electromyographic recordings, and a new digital inertial measurement unit to quantify 33 body kinematics, red muscle activity, and 3D orientation and centre of mass acceleration during 34 forward accelerations and steady swimming over several speeds. During acceleration, fish co-35 activated anterior muscle on the left and right side, and activated all muscle sooner and kept it 36 active for a larger fraction of the tail beat cycle. These activity patterns are consistent with our 37 hypothesis that fish use their red muscle to stiffen their bodies during acceleration. We suggest 38 that during impulsive movements, flexible organisms like fishes can use their muscles not only 39 to generate propulsive power but to tune the effective mechanical properties of their bodies, 40 increasing performance during rapid movements and maintaining flexibility for slow, steady 41 movements. 42

Experimental–numerical method for calculating bending moments in swimming fish shows that fish larvae control undulatory swimming with simple actuation

“…For accelerating motions, swimming kinematics have been observed to be similar and hydrodynamically optimal across a wide range of body shapes and sizes [ 46 ]. In bluegill sunfish, muscle activation patterns have been measured during acceleration, showing that they effectively stiffen their bodies by coactivating muscles on both sides of the body [ 47 ]. This raises an interesting question: Is this activation pattern conserved across fish species to effectively produce acceleration?…”