Meeting Abstract

69.2  Monday, Jan. 6 08:15  The relationship between muscle cross-sectional area and locomotor performance in lizards SCALES, J.A.*; BUTLER, M.A.; Univ. of Hawaii, Manoa; Univ. of Hawaii, Manoa jscales@hawaii.edu

Locomotor performance is essential to the fitness of many terrestrial vertebrates. Therefore, determining what defines locomotor performance is an integral part of understanding the evolution of morphology, physiology, and behavior of vertebrates. Recent work suggests that the amount of force and the rate at which force is applied to the ground may limit performance, indicating that force production is a key driver of performance abilities. The cross-sectional area (CSA) of a muscle is a significant determinant of peak force production capabilities, suggesting that CSA may influence performance abilities. However, few studies examine how muscle CSA actually impacts performance, especially in a comparative context. Here we examine how the CSA of muscles of the hindlimb are related to acceleration, sprint speed, and exertion in 21 species of lizards. We find that total muscle CSA scales isometrically in these lizards, with increases in both stance and swing phase musculature. Furthermore, speed and acceleration, but not exertion increase with CSA, and the CSA of stance phase muscles better predicts speed and acceleration abilities than swing phase muscles. Fast lizards show increased stance phase CSA, but the distribution of CSA across joints varies, suggesting that there is more than one way to achieve high speeds and acceleration. We conclude that muscle CSA plays an important role in defining some, but not all performance capabilities, and that there may be multiple muscle designs to achieve similar performances.