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First published online January 12, 2004
Journal of Experimental Biology 207, 667-674 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00808

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Moments and power generated by the horse (Equus caballus) hind limb during jumping

Darren J. Dutto^1,*, Donald F. Hoyt², Hilary M. Clayton³, Edward A. Cogger⁴ and Steven J. Wickler⁴

¹ Department of Kinesiology and Health Promotion, California State Polytechnic University, Pomona, CA 91768, USA
² Department of Biological Sciences, California State Polytechnic University, Pomona, CA 91768, USA
³ College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA
⁴ Department of Animal and Veterinary Science, California State Polytechnic University, Pomona, CA 91768, USA

View larger version (98K): [in a new window]   Fig. 1. The picture shows the reflective marker set-up with four joints of the hind limb. The locations of the knee and hip joints were mathematically determined using the geometrical relationships of the limb segments. Digitized coordinates were used to determine the knee, and the mathematically derived coordinates of the knee and the digitized coordinates of the tuber coxae were used to calculate the hip coordinate (see Materials and methods). The location of the hip (xh, yh) was determined using the coordinates of the knee (xk, yk) and tuber coxae (xt, yt), and the lengths of the pelvis (lpelvis) and thigh (lthigh) segments. If two circles are drawn with the tuber coxae and knee joint as origins and radius equivalent to the length of the appropriate segments, there will be two places where the circumferences of the circles overlap (or one if the segments are oriented in a straight line). The rearmost of these two intersections was taken as the location of the hip joint.

View larger version (19K): [in a new window]   Fig. 2. Representation of the inertial moment relative to the joint moments for one jumping trial. The solid symbols are the total joint moment for each identified joint. The open symbols represent the inertial moments. Notice that the inertial moments are clustered near zero throughout the trial. MP, metatarsophalangeal joint.

View larger version (30K): [in a new window]   Fig. 3. Joint moments (relative to body mass) are presented. (A) Observed moments at the hip for each of the test animals. Each curve represents the mean of the trials for that animal, with the number of trials ranging between five and eight for the different animals. The five curves are very similar across animals. (B) Moments for the MP (metatarsophalangeal), ankle, knee and hip joints of the hind limb. Each curve represents the mean of 29 trials (solid line) ± S.D. (shaded area) across all horses. For both plots, positive values represent extensor moments and negative values represent flexor moments for each joint.

View larger version (34K): [in a new window]   Fig. 4. Mean angular position data for all trials of the hind limb joints are presented (29 trials included in the mean). Each curve represents a mean (solid line) ± S.D. (crossbars) for the respective joint. Decreasing angles represent joint flexion and increasing angles represent joint extension. MP, metatarsophalangeal joint.

View larger version (42K): [in a new window]   Fig. 5. Joint power (relative to body mass) for the MP (metatarsophalangeal), ankle, knee and hip joints of the hind limb during ground contact. Each curve is the mean of 29 trials (solid line) ± S.D. (shaded area) of the power. Positive values represent power generation and negative values represent power absorption.

View larger version (26K): [in a new window]   Fig. 6. Net power created by the hind limb during the jump. The curve represents the mean of 29 trials (solid line) ± S.D. (shaded area) of the summed power from the four joints of the hind limb.

View larger version (13K): [in a new window]   Fig. 7. During the first 40% of contact (when the total power is primarily negative), the mean horizontal velocity of the tuber coxae increased and the mean vertical velocity changed from negative to approximately 0. The resultant velocity remains essentially constant (the same value at the beginning and end of the time period) during the first 40% of contact. During the last 60% of contact, the horizontal velocity remains essentially constant until near the end, and the vertical velocity substantially increases; thus, the resultant velocity increases almost continuously over the final 60% of contact. 40% of contact is indicated by the vertical line. Velocity values represent the mean across all trials.

View larger version (14K): [in a new window]   Fig. 8. The horizontal ground reaction force is only negative for the first 25% of ground contact, which means that the force vector stays anterior to the knee (the leg) throughout ground contact. Horizontal velocity decreases slightly during the first 25% of contact, which coincides with the negative (braking) horizontal force. For comparison, the mean horizontal force during trotting at 3.25 m s-1 (which is a speed very similar to mean speed during the jump) is shown. The amount of braking that occurs during trotting is greater (larger area) than during jumping. The braking impulse during trotting is roughly twice that of jumping (0.06 Ns kg-1 vs 0.03 Ns kg-1). The curve represents the mean horizontal force for all trials.