BIKNEVICIUS, A.R.; STEVENS, N.J.; Ohio University College of Osteopathic Medicine; Ohio University College of Osteopathic Medicine: Energy balance or limb alignment? A look at the trailing and leading limbs of galloping dogs.

Limb pairs in galloping animals are distinguished as leading and trailing by their position: although the trailing limb lands first, it occupies a position behind the leading limb when both are on the ground. Alexander, Jays and Ker (1980) posited that animals should make use of tendon elasticity as a passive spring mechanism to reduce the metabolic energy costs of locomotion, and their model predicts trailing limbs to be relatively more accelerative and leading limbs to be relatively more decelerative in order to balance negative and positive work across the limb pair. Subsequent studies have yielded equivocal results. The present study combines force platform data with synchronized high-speed videography for a large sample of dogs utilizing a rotary gallop. Our results suggest that while peak vertical forces and breaking impulses of leading and trailing hindlimbs are largely equivalent, trailing hindlimbs take on a greater role in accelerating forward the center of mass. Because a greater braking role was not observed in the leading limb, the energy balance hypothesis is unsupported. However, a more potent factor driving limb pair function may be maintenance of low bone stresses at high speeds. Hence, animals may act to reduce stresses on hindlimbs by altering the effect of substrate reaction force on bone stress via changes in limb joint angles. This limb alignment model predicts that peak ground reaction forces will more closely align with the long axis of the long bones in both leading and trailing hindlimbs, thereby reducing bending strains experienced in that region. We evaluate this model for the tibia.