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First published online August 31, 2004
Journal of Experimental Biology 207, 3507-3514 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01171

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Ground reaction forces in horses trotting up an incline and on the level over a range of speeds

Darren J. Dutto^1,*, Donald F. Hoyt², Edward A. Cogger³ and Steven J. Wickler³

¹ Department of Kinesiology and Health Promotion, California State Polytechnic University, Pomona 91768, USA
² Department of Biological Sciences, California State Polytechnic University, Pomona 91768, USA
³ Department of Animal and Veterinary Science, California State Polytechnic University, Pomona 91768, USA

View larger version (31K): [in a new window]   Fig. 1. Ground reaction force (GRF) patterns are similar to those typically reported for other quadrupeds. Both vertical (A,C,E,G) and horizontal (B,D,F,H) forces are depicted for the level and the incline. Thicker lines represent faster (>4.5 m s–1) and the thinner lines represent slower (<2.75 m s–1) speeds. Forces generated by the forelimb increased as speed increased for both the level (A) and incline (C) conditions. Hindlimb vertical forces tended to remain constant on the level (E), but increased on the incline (G). Hindlimb forces were higher on the incline than on the level.

View larger version (23K): [in a new window]   Fig. 2. Temporal characteristics decreased with speed, and were the same for the forelimb on level and incline conditions, but higher for the hindlimb on the incline. In this and subsequent figures the following symbols and lines are used: black, level; red, incline; forelimb on the level, filled squares; forelimb on the incline, filled triangles; hindlimb on the level, open squares; hindlimb on the incline, open triangles; solid lines, forelimb; broken lines, hindlimb. (A) Time of contact on the level decreased with speed as a power function (see Table 1). Time of contact tc was lower for the hindlimb, but values converged at higher speeds. (B) Time of contact of the forelimb was essentially the same on the incline as on the level, but slightly higher for hindlimb than on the level. For easy reference, the black lines represent the data on the level.

View larger version (25K): [in a new window]   Fig. 3. On the level, peak vertical force Fz,peak under the forelimb increased as a function of speed but the forces under the hindlimb remained constant at all trotting speeds (A). On an incline (B), force increased with speed in both limbs but was lower in the forelimb than on the level. The bottom figure shows the incline condition with the regression lines from the level condition. Symbols and lines are explained in the legend to Fig. 2.

View larger version (39K): [in a new window]   Fig. 4. Vertical impulse Impz decreased with increased speed for both limbs in both conditions (A). Vertical impulse generated by the forelimb was lower on the incline than on the level but vertical impulse generated by the hindlimb was higher on the incline than on the level. Using the vertical impulse to determine the average force generated over a stride (B) shows that on the level the force is distributed so that the force distribution is 57%/43% fore/hind (the values in the figure are force values, but expressed as a percentage in Table 1). On the incline the average force distribution was 52%/48% fore/hind respectively. Symbols and lines are explained in the legend to Fig. 2.