Meeting Abstract
102.3 Sunday, Jan. 6 Scale effects and rotational inertia in the limbs of quadrupedal mammals KILBOURNE, B.M.; University of Chicago brandon.kilbourne@uni-jena.de
Recent biomechanical studies have revealed that the metabolic cost of swinging the limbs is a significant portion of the total metabolic cost of terrestrial locomotion. Such studies suggest that limb rotational inertia, which reflects gross limb morphology, is relevant to understanding the mechanical cost of terrestrial locomotion. Yet scant data on limb inertial properties currently exist. Limb inertial properties – moment of inertia (MOI), mass, and radius of gyration – were measured from the fore- and hindlimbs of 44 species of quadrupedal mammals (representing eight major clades) to understand how limb rotational inertia varies with body and limb size. Muscles were left in situ on limb bones in order to measure limb inertial properties for the entire appendicular musculoskeletal system. Relative to body mass, limb length is positively allometric, with larger mammals having longer limbs relative to their body mass than smaller mammals. Fore-and hindlimb MOI is negatively allometric with limb length, with an allometric exponent of ~ 4.45 being significantly less than the predicted slope (5.0). Though the difference in actual and predicted exponents seems small, the negative allometry of hindlimb MOI results in a considerable decrease in MOI in larger limbed mammals relative to the predictions of geometric similarity. Thus, relative to limb length, larger mammals have limbs that consume less energy to swing than smaller mammals. Fore- and hindlimb mass scale with negative allometry relative to limb length. Radius of gyration – a measure of limb shape – scales with negative allometry (hindlimbs) or isometry (forelimbs) relative to limb length. Thus, hindlimb mass shifts proximally relative to hindlimb length with increasing limb size in mammals. Positive allometry of limb length and the negative allometry of limb inertial properties have a high potential to reduce the locomotor costs of large mammals relative to their size.
