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First published online January 19, 2006
Journal of Experimental Biology 209, 455-465 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02029

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Dynamically similar locomotion in horses

Sharon R. Bullimore^* and Jeremy F. Burn

Department of Anatomy, University of Bristol, Southwell Street, Bristol, BS2 8EJ, UK

View larger version (18K): [in a new window]   Fig. 1. Consequences of the nonlinear stress-strain relationship of tendon for the scaling of tendon strain. Data of Riemersma and Schamhardt (1985) for equine superficial digital flexor tendon. Because the tendon is stiffer at higher stresses, a given increase in stress causes a smaller increase in strain when it occurs at a higher initial stress (compare shaded regions). A consequence of this is that the scaling exponent for strain is lower than the scaling exponent for stress. For example, over the part of the curve within and between the shaded regions, a stress proportional to causes a strain proportional to . Therefore, a nonlinear tendon stress-strain relationship can reduce the effects of size differences on tendon strain.

View larger version (21K): [in a new window]   Fig. 2. Relationships of relative stride length (RSL) and duty factor (DF) to body mass (Mb) in horses trotting at three different Froude numbers (Fr). Allometric equations describing the data are shown (scaling exponents given ± 95% confidence intervals) and are indicated by the solid lines. The scaling exponents were not significantly different from 0, indicating that RSL and DF are independent of body mass in horses trotting at equal Froude number.

View larger version (13K): [in a new window]   Fig. 3. Measured and predicted relationships of relative stride length (RSL) to body mass (Mb) in horses trotting at a Froude number of 0.5. Crosses are measured values, solid line is allometric equation fitted to measured values , broken line is relationship predicted with linear tendon properties , circles are relationship predicted with realistic nonlinear tendon properties . The predicted effect of size is substantially reduced by taking into account the nonlinear properties of tendon, but is still greater than measured experimentally. This suggests that additional factors compensate for size effects in horses.