RICHARDS, Christopher T.*; BIEWENER, Andrew A.; Harvard University; Harvard University: Measuring muscle power in vivo and in vitro: Identifying mechanisms by which power is modulated in the Xenopus laevis plantaris muscle during swimming

During swimming, in vivo power output of the plantaris is obtained by simultaneous recording of muscle activation (by electromyography), length (by sonomicrometry) and force (using a calibrated stain gauge transducer fastened to the plantar tendon). Following in vivo measurements, the plantaris is excised from the animal and mounted to a computer-driven lever arm controlling muscle length while measuring force. Patterns of muscle strain and activation timing (previously collected from the intact animal) are imposed to simulate in vivo conditions. In vivo data shows plantaris power output ranging from 0.19 to 75.92 W/kg, which is correlated with changes in muscle strain rate, peak strain and peak force. Although in vitro data is currently too preliminary for conclusive results, we address the question: can in vivo muscle power can be predicted from muscle strain and activation data? And we seek to test which parameters (strain magnitude, strain rate and activation timing) most strongly contribute to variation in muscle power both within and beyond the range of muscle function observed in vivo.