Biomechanics of the rostrum in crocodilians: A comparative analysis using finite-element modeling

This article reports the use of simple beam and finite-element models to investigate the relationship between rostral shape and biomechanical performance in living crocodilians under a range of loading conditions. Load cases corresponded to simple biting, lateral head shaking, and twist feeding behaviors. The six specimens were chosen to reflect, as far as possible, the full range of rostral shape in living crocodilians: a juvenile Caiman crocodilus, subadult Alligator mississippiensis and Crocodylus johnstoni, and adult Caiman crocodilus, Melanosuchus niger, and Paleosuchus palpebrosus. The simple beam models were generated using morphometric landmarks from each specimen. Three of the finite-element models, the A. mississippiensis, juvenile Caiman crocodilus, and the Crocodylus johnstoni, were based on CT scan data from respective specimens, but these data were not available for the other models and so these-the adult Caiman crocodilus, M. niger, and P. palpebrosus-were generated by morphing the juvenile Caiman crocodilus mesh with reference to three-dimensional linear distance measured from specimens. Comparison of the mechanical performance of the six finite-element models essentially matched results of the simple beam models: relatively tall skulls performed best under vertical loading and tall and wide skulls performed best under torsional loading. The widely held assumption that the platyrostral (dorsoventrally flattened) crocodilian skull is optimized for torsional loading was not supported by either simple beam theory models or finite-element modeling. Rather than being purely optimized against loads encountered while subduing and processing food, the shape of the crocodilian rostrum may be significantly affected by the hydrodynamic constraints of catching agile aquatic prey. This observation has important implications for our understanding of biomechanics in crocodilians and other aquatic reptiles.

Biomechanical and physiological comparison of conventional webbing and the M83 assault vest

This study compared the effect of load distribution using two different webbing designs on oxygen consumption and running kinematics of soldiers. It was hypothesised that running with webbing that distributes the load closer to the body (M83 Assault Vest) would expend less energy compared to running with conventional webbing (CON). Seven soldiers randomly completed three treadmill trials; an unloaded VO(2)max test, and two loaded (8 kg) efficiency tests using either the M83 or CON webbing. The VO(2)max test and the loaded efficiency tests had 4-min stages at 5, 8, 10 and 12km h(-1). Energy expenditure was measured via indirect calorimetry and video analysis was used to determine stride frequency (SF) and stride length (SL) during each trial. Participants using the M83 webbing expended significantly (p < 0.05) less energy at all four running velocities compared to the CON trials. The M83 webbing resulted in smaller changes to SL and SF from the unloaded trial when compared to the CON trial. These results indicate that the M83 vest that is designed to distribute the load closer to the body may have an energy efficiency advantage over conventional webbing when soldiers are running. (C) 2004 Published by Elsevier Ltd.