Meeting Abstract

P1.162  Monday, Jan. 4  The Scaling of Limb Rotational Inertia in Quadrupedal Mammals KILBOURNE, Brandon M; University of Chicago bmkilbou@uchicago.edu

Recent biomechanical studies have revealed that the metabolic cost of swinging the limbs is a significant portion of the total metabolic cost of locomotion. Such studies suggest that the rotational inertia of limbs is relevant to understanding the mechanics and energetics of terrestrial locomotion. However, scant data on limb inertial properties currently exist. Data on limb inertial properties – limb mass, moment of inertia, center of mass position, and natural frequency – were collected from the fore- and hindlimbs of 17 species of quadrupedal mammals (representing nine families) in order to understand how limb rotational inertia varies with body size. Muscles were left in situ on limb bones in order to measure limb inertial properties for the entire appendicular musculoskeletal system. To standardize comparisons, inertial properties were measured for limbs only in the extended position. As a function of body mass, limb mass scales according to geometric similarity, with limb mass being a constant fraction of body mass across mammals. Fore-and hindlimb center of mass position both scale isometrically with body mass. As a percentage of limb length, fore- and hindlimb center of mass position are independent of body size. Fore- and hindlimb moment of inertia also both scale isometrically with body mass. In both the fore- and hindlimbs, the scaling of limb natural frequency is also not significantly different from the predictions of geometric similarity. The correlation between limb natural frequency and body mass is negative, paralleling the scaling of stride frequency between small and large mammals. The regularity of changes in limb inertial properties with body mass should allow for inferences of limb inertial properties of extinct mammals, given that reasonable estimates of body mass can be made.