Allometry of Felid Knee and Elbow Effective Mechanical Advantage

Abstract

Body size has a profound impact on animal locomotion because all terrestrial animals must support and move their mass against gravity. If large animals were isometrically scaled versions of smaller animals, then larger animals would have relatively weaker muscles and bones, as both are a function of area. The loads associated with locomotion however, are largely equivalent to body mass, a function of volume. To contend with this problem, larger animals have been observed to use more extended limb postures; increasing the effective mechanical advantage (EMA) of their muscles. Felids however, maintain the same limb posture across body sizes, suggesting they are not increasing EMA through limb extension. To investigate how felids maintain the same posture across body sizes we analyzed the relationship between the EMA of the triceps brachii and quadriceps and body mass in nine species of felids with kinematic data from the literature.Ulnae (n=37) and femora (n=30) of nine species of felids were surface scanned using a 3D NextEngine laser scanner. Linear measurements were taken on the tibia, patella, talus, calcaneus, navicular, third cuneiform and third metatarsal. Ulna and femur surface models were aligned in virtual space using anatomical and biomechanical axes. Triceps brachii EMA was calculated as the ratio of the muscle lever arm to the GRF lever arm, which were both collected on the ulna surface model. The quadriceps muscle and GRF lever arms were calculated using the femur surface models, linear measurements of limb and foot bones and kinematic data. Joint EMAs, muscle lever arms and GRF lever arms were regressed against body mass using PGLS regressions incorporating a phylogeny from 10kTrees. Pagel's λ was zero for all analyses, so data were reanalyzed using reduced major axis (RMA) regressions without phylogenetic information.The triceps brachii and quadriceps EMA scale to body mass with slopes of 0.15 and 0.13, respectively, indicating positive allometry, meaning that larger felids have a relatively greater EMA and suggesting that some aspect of felid joint morphology is altered. For both joints neither the muscle lever arms nor the GRF lever arms are statistically different from isometry, however the muscle lever arms generally trend toward positive allometry, while the GRF lever arms lean toward negative allometry. This indicates that either there are subtle changes to both lever arms or that different felid species accomplish an increased EMA in distinct ways.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.