Meeting Abstract
Decades of comparative research have established that across adult eutherian mammals, peak loads during locomotion rarely reach above 25-50% of bone structural capacity, maintaining safety factors (peak strength/peak locomotor stress) between 2 and 4. In contrast, existing data suggest that safety factors are not maintained during growth, but rather decline with age. As such, juvenile mammals are relatively “overbuilt”, permitting them to exhibit adult-like levels of locomotor performance with reduced risk of skeletal injury. Here, we expand this dataset by examining the ontogeny of hind limb bone safety factors in Eastern cottontail rabbits (Sylvilagus floridanus). We used a combination of in vivo locomotor performance testing, free-body modeling, and in vitro material properties data to characterize ontogenetic changes in locomotor loading, long bone strength, and safety factor in S. floridanus. Peak long bone stresses during high-speed locomotion scaled to body mass with isometry (femur: M0.385±0.246; tibia: M0.261±0.150). Because the maximum bending strength of the femur and tibia similarly scaled with isometry (femur: M0.307±0.132; tibia: M0.307±0.307), safety factor was maintained between 2.5 and 2.6 in the femur and between 3.1 and 3.3 in the tibia across an order of magnitude in body size growth (106-1,277g range in body mass). Though our findings contrast with previous studies of mammalian long bone growth, rabbits are smaller than most previously studied taxa and have relatively reduced home ranges, perhaps mitigating the need for increased safety factors early in life. Supported by NSF IOS-1146916.
