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First published online January 5, 2005
Journal of Experimental Biology 208, 249-260 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01373

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Contribution of the forelimbs and hindlimbs of the horse to mechanical energy changes in jumping

Maarten F. Bobbert^1,* and Susana Santamaría²

¹ Institute for Fundamental and Clinical Human Movement Sciences, Vrije Universiteit, van der Boechorstraat 9, NL-1081 BT Amsterdam, The Netherlands
² Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 12, NL-3584 CM Utrecht, The Netherlands

View larger version (9K): [in a new window]   Fig. 1. Locations of anatomical markers (A) and definitions of joint angles (B). (A) Markers indicated with a star were used to construct a template of the trunk. Markers were in the following locations: 1, left crista facialis (cranial); 2, left wing of atlas; 3, spinous process of T6 (withers); 4, spinous process of T13; 5, spinous process of L2; 6, spinous process of L5; 7, spinous process of S2; 8, spinous process of S5; 9, left tuber coxae; 10, greater trochanter of the left femur; 11, lateral epicondyle of the left femur; 12, lateral side of distal end of the left talus; 13, lateral side of the head (distal end) of the 3rd metatarsal bone; 14, lateral side of the coronet of the left hind hoof; 15, medial side of the coronet of the right hind hoof; 16, right radial carpal bone; 17, medial side of the head (distal end) of the 3rd metacarpal bone; 18, medial side of the coronet of the right front hoof; 19, lateral side of the coronet of the left front hoof; 20, lateral side of the head (distal end) of the 3rd metacarpal bone; 21, left ulnar carpal bone; 22, lateral epicondyle of the left humerus; 23, greater tubercle (caudal part) of the humerus; 24, tuber of the left spina scapulae; 25, transverse process of C6. (B) Joint angles () were calculated for the left hip, left stifle, left hock, left metatarsophalangeal joint (mtp), left metacarpophalangeal joint (mcp), left carpal joint, left elbow joint, and left shoulder joint.

View larger version (25K): [in a new window]   Fig. 2. Typical time histories of the vertical acceleration of the centre of mass (yCOM) and of the height of the coronet yc of each four hoofs during a jump in which the left forelimb was trailing. Time is expressed relative to the instant of take-off (t=0). Note that the experiments occurred in a sandy arena, which explains why the distance of the coronet to the ground may vary.

View larger version (28K): [in a new window]   Fig. 3. Average stick diagrams for several instants (see inset) during the forelimb and hindlimb push. Diagrams were constructed from the average marker positions of the horses and the calculated ground reaction force vector (arrows). From each of 23 horses one jump was used in which the left forelimb limb was leading and one in which it was trailing. For each jump, time was normalized separately for the forelimb push and for the hindlimb push, and subsequently results were averaged over horses. Results for the hindlimb push are for the jumps in which the left forelimb was leading. Note the direction of the x axis. Circles indicate the COM.

View larger version (22K): [in a new window]   Fig. 4. Average time histories of (A) total power output (tot), (B) the horizontal component of the calculated ground reaction force (FGR,x) and (C) the vertical component of the calculated ground reaction force (FGR,y). From each of 23 horses one jump was used in which the left forelimb limb was leading and one in which it was trailing. For each jump, time was normalized separately for the forelimb push and for the hindlimb push, and subsequently results were averaged over horses and jumps, regardless of lead. Solid lines indicate averages; broken lines indicate 95% confidence intervals.

View larger version (18K): [in a new window]   Fig. 5. (A-E) Average time histories of energy components. From each of 23 horses one jump was used in which the left forelimb limb was leading and one in which it was trailing. For each jump, time was normalized separately for the forelimb push and for the hindlimb push, and subsequently results were averaged over horses and jumps, regardless of lead. Solid lines indicate averages; broken lines indicate 95% confidence intervals. Dash-dotted lines indicate 95% confidence intervals obtained when the individual curves were first corrected for the mean value. (A) Etot, total mechanical energy; (B) Ekin,COM,x, kinetic energy due to the horizontal velocity of the centre of mass; (C) Ekin,COM,y, kinetic energy due to the vertical velocity of the centre of mass; (D) Epot, potential energy; (E) Erot, rotational energy. The kinetic energy due to the velocity of segmental mass centres relative to the mass centre of the body was negligible and is not shown.

View larger version (23K): [in a new window]   Fig. 6. Average time histories of selected distances L in the forelimb and hindlimb. From each of 23 horses one jump was used in which the left forelimb limb was leading and one in which it was trailing. For each jump, time was normalized separately for the forelimb push and for the hindlimb push, and subsequently results were averaged over horses. Results for the hindlimb push were averaged over all jumps regardless of lead. Solid lines indicate averages; broken lines indicate 95% confidence intervals. Dotted curve for distance elbow-coronet in the trailing forelimb represents the result obtained with uncorrected skin marker positions. TSS, tuber of spina scapulae.

View larger version (25K): [in a new window]   Fig. 7. Average time histories of joint angles as well as total length L of the limbs. TSS, tuber of spina scapulae. From each of 23 horses one jump was used in which the left forelimb limb was leading and one in which it was trailing. For each jump, time was normalized separately for the forelimb push and for the hindlimb push, and subsequently results were averaged over horses. Results for the hindlimb push were averaged over all jumps regardless of lead. Solid lines indicate averages; broken lines indicate 95% confidence intervals. Dotted curves for the elbow angle and shoulder angle in the trailing forelimb represent the average results obtained with uncorrected skin marker positions.

View larger version (19K): [in a new window]   Fig. 8. Average time histories of forces carried by the left forelimb. From each of 23 horses one jump was used in which the left forelimb limb was leading and one in which it was trailing. Force magnitude F was estimated from the distance between elbow and coronet, assuming that this part of the leg operated like a linear spring with a stiffness of 166 N m-1 kg-1. For each jump, time was normalized separately for the forelimb push and for the hindlimb push, and subsequently results were averaged over horses. The top diagram shows the sum of the two curves, to be compared with the calculated ground reaction force in Fig. 4. Solid lines indicate averages; broken lines indicate 95% confidence intervals.