43.2 Saturday, Jan. 5 Tendon function during swimming: does compliance enhance performance? RIVERA, A.R.V.*; CHOUDHURY, U.; RICHARDS, C.T.; Rowland Institute at Harvard; Rowland Institute at Harvard; Rowland Institute at Harvard firstname.lastname@example.org
Tendons can enhance performance by storing elastic energy produced by the muscle, then releasing it rapidly during recoil, assisting the muscle to accelerate the load. Under certain conditions, tendon dynamics cause ‘power amplification’, where peak muscle-tendon (MT) power exceeds the theoretical limits of contractile element (CE) power. While power amplification is likely in jumping, its role during swimming is less known. Recent models of MT dynamics during hydrodynamic loading suggest that multiple morphological configurations may maximize MT power, sometimes causing power amplification. However, as this work was performed in still water, it is unclear whether compliant tendons enhance or reduce swimming speed. To address this, we used a forward translating bio-robotic foot actuated by motors simulating Xenopus laevis muscle dynamics. We simulated muscle contractions with and without translation at tendon stiffness values ranging from 750 to 30,000 N/m allowing us to relate MT and whole body swimming performance. While peak CE power was similar with and without translation, and across stiffness levels, peak MT power increased with decreasing stiffness with translation, but not in still water. Differences in peak MT power with and without translation stem from timing differences in tendon recoil (starting earlier and lasting ~2x as long without translation). Among translational cases, we observed power amplification for all but the stiffest tendon; for example, in the most compliant case, peak MT power was ~33% greater than the limit for muscle alone. However, there was no enhancement of either swimming speed or muscle work as compliance increased. Hence, it remains unclear whether tendon compliance is beneficial for swimming performance.