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First published online April 8, 2004
Journal of Experimental Biology 207, 1715-1728 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00947

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Effects of mass distribution on the mechanics of level trotting in dogs

David V. Lee^*, Eric F. Stakebake, Rebecca M. Walter and David R. Carrier

Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112-0840, USA

View larger version (54K): [in a new window]   Fig. 1. (A) Simultaneous fore- and hindlimb supports were recorded by two separate force platforms (thick lines) during trotting. (B) Ground reaction forces were measured independently by the two force platforms. Solid lines indicate vertical force and broken lines fore–aft force. BW, body weight.

View larger version (6K): [in a new window]   Fig. 2. Illustration of braking–propulsive biases defined by different values of the Fourier shape ratio a1/b2. a1/b2 = –0.5 indicates a braking bias, a1/b2 = 0 indicates no b–p bias, and a1/b2 = 0.5 indicates a propulsive bias.

View larger version (14K): [in a new window]   Fig. 3. Fore- and hindlimb force curves reconstructed from steady speed Fourier coefficients predicted at 2.86 m s–1 (see Materials and methods and Appendix B) for each of the loading conditions (U, unloaded; M, mid-load; F, fore-load; H, hind-load). Solid lines indicate vertical force and broken lines fore–aft force.

View larger version (28K): [in a new window]   Fig. 4. Steady speed values (±95% CI) of mean fore–aft force (filled bars) and braking–propulsive bias a1/b2 (open bars) for the loading conditions U, M, F and H (see text). Significant difference (P<0.05) from the unloaded condition U is indicated by an asterisk.

View larger version (15K): [in a new window]   Fig. 5. (A) The kinematic mid-point between the eye and the base of the tail is represented by the vertical line posterior to the elbow. The distance p between hindlimb and forelimb centers of pressure was measured from force platform data and was partitioned according to this mid-point. (B) Distances from the mid-point to the hindlimb (open bars) and forelimb (filled bars) centers of pressure for the loading conditions U, M, F and H (see text). Error bars indicate 95% confidence intervals. Significant difference (P<0.05) from the unloaded condition U is indicated by an asterisk.

View larger version (12K): [in a new window]   Fig. 6. Trunk mechanics during trotting with a mid-trunk load. The load tends to ventroflex the trunk. Hindlimb retractors and forelimb protractors exert moments that tend to dorsiflex the trunk. Hypaxial muscle tension also tends to dorsiflex the trunk.

View larger version (17K): [in a new window]   Fig. 7. (A) Fore–aft GRF of trotting dog with R0=0.65, based upon the unloaded b–p biases (a1/b2) from Fig. 4 and duty factors (DF) from Table 4. (B) A hypothetical quadruped with R0=0.50, showing equal fore- and hindlimb magnitudes of b–p bias and equal duty factors. (C) A hypothetical quadruped with R0=0.35, showing a reversal of the fore- and hindlimb patterns observed in trotting dogs.