Meeting Abstract
P1.112 Tuesday, Jan. 4 Development of a hydrodynamic sensor for measuring time varying forces during a robotic frog kick in water. CLEMENTE, CJ*; RICHARDS, C; Harvard University; Harvard University clemente@rowland.harvard.edu
A fundamental feature of vertebrate muscle is that maximal forces are generated over a limited range of lengths and velocities. This means that muscle dynamics are not only governed by neural activation, but also by direct feedback from the environment. While some studies have attempted to determine this in terrestrial locomotion, few studies have measured this in aquatic environments, probably because the estimation of forces is difficult in aquatic systems. To examine the interplay between muscle dynamics and environment in aquatic systems we developed a hydrodynamic force sensor, capable of mN resolution, based on rotation at the ankle joint of the aquatic frog Xenopus laevis. The sensor was designed to be insensitive to lever arm effects, therefore resistive hydrodynamic forces could be measured directly without estimations of the hydrodynamic centre of pressure. The movement of the sensor through water was powered by a computer generated muscle model, which, using a feedback loop at 10 kHz, simulated the force-length and force-velocity effects of vertebrate muscle. We then used this setup to simulate the effect of changing the hydrodynamic load by increasing and decreasing foot size. Preliminary results indicate that while both muscle forces and hydrodynamic forces increased with foot size, the muscle power showed a decrease with increasing footsize, due to a drop in the shortening velocity of the muscle, reflecting previous results for live frog muscle. However, hydrodynamic power showed an increase with increasing footsize, despite a decrease in foot velocity. These results indicate a complex interaction between force-length and force-velocity characteristics of vertebrate muscles with the hydrodynamic environment, and outlines the advantages of using model based system to understand muscle dynamics.
