### Meeting Abstract

**33.1** Thursday, Jan. 5 **Limitations to swimming speed in drag based aquatic systems** *CLEMENTE, CJ*; RICHARDS, CT; Harvard University; Harvard University* clemente@rowland.harvard.edu

Within terrestrial systems, the fastest sprinters are neither the largest, nor the smallest, but are intermediately sized. The initial increase in speed is because stride length increases more rapidly than stride frequency decreases as animals get larger. Yet above a certain size, locomotory performance is constrained due to the effects of body weight causing mechanical stress on musculoskeletal designs. However, in aquatic systems, organisms can achieve neutral buoyancy and therefore the effects of mass related stress increases are likely to be smaller. This leads to the question, of what is limiting speed in drag based aquatic systems. How much do the force-length and force-velocity properties of the muscular skeletal system limit total performance? To answer these questions we measured swimming speed in the aquatic frog * Xenopus leavis *, for individuals ranging in body mass from 1g to 200g. We then created a mathematical rowing frog model, incorporating the force-length and force-velocity effects, along with the scaling exponents for morphological features, to assess if these variables can limit maximal swimming performance. Measurements for sprint speeds of * X. leavis * using high speed video (250 Hz) suggest that speed initially increases with body size from 0.84 m.s^{-1} for 1g frogs (mean = 1.28g) up to 1.36 m.s^{-1} for 20g frogs (mean = 20.12). However further increases in body size did not result in greater swimming speeds (i.e. 200g frogs swam at 1.35 m.s^{-1}). The virtual frog model, underestimated maximal sprint speed achievable (0.51 m.s^{-1}) but did predict an optimal body size with respect to swimming speed at 120g, after which maximum speed declined. Preliminary analysis of the model suggests that propulsive drag produced by the feet, and therefore musculoskeletal force-velocity effects may limit speed in drag based aquatic systems.