60.3 Friday, Jan. 6 Size-related biomechanical constraints on foot impacts in ungulate mammals. WARNER, S E*; PICKERING, P; PANAGIOTOPOULOU, O; PFAU, T; REN, L; HUTCHINSON, J R; Royal Veterinary College; Royal Veterinary College; Royal Veterinary College; Royal Veterinary College; University of Manchester; Royal Veterinary College email@example.com
Understanding the mechanics of foot impact and its relationship with animal size may improve our ability to detect, prevent and treat foot disease. Newtonian mechanical principles suggest that heavier animals have a larger effective foot mass (Meff); this may contribute to greater impact forces that could initiate impact injury. So, for example, how can a 3000kg elephant safely control ~150kg of foot mass with every step? We hypothesised that Meff is modulated to ensure impact forces remain fairly constant in ungulates of increasing size. Using standard force-platform (1000Hz; Kistler, 200Hz; AMTI) and motion capture (250Hz; Qualisys or AOS high speed camera) methods we measured limb kinematics and kinetics in eleven species ranging from 18kg (blackbuck antelope) to 3157kg (Asian elephant). As ungulates get heavier, the forefoot Meff exhibits surprisingly strong negative allometry at slow running speeds; conversely, the hindfoot Meff has at least weak positive allometry at walking speeds. Impact force amplitude scales with isometry and peak GRF scales with negative allometry at dynamically similar speeds. Curiously, increased Meff is not reflected in the impact force amplitude, which remains a fraction of the GRF peak. These mechanisms show how ungulates keep impact amplitude from becoming a more prevalent cause of impact injury.