The influence of weighted heel boots on the duration and start of the stance phases of all four limbs in slow and fast Tolt in the Icelandic Horse

Abstract

The gait pattern of tolt with weighted heel boots placed on the forelimbs differs from tolt without heel boots. The aim of the study was the documentation of the influence of weighted heel boots on the tolt gait pattern, especially on the pattern of stance phases of all four limbs, with single limb support, two limb support and three limb support phases, both in slow and in fast tolt. Eight sound Icelandic horses (age: 12±3 years, body mass: 369±46 kg) were measured during ridden tolt on the treadmill. Reflecting markers were placed on the skin above the frontal bone, the sacral bone, and all four hooves. Marker movement was traced using a high speed video system (Motion Analysis Corp., 10 cameras, measurement frequency 120 Hz, resolution 1,3 Megapixel). After training on the treadmill without the rider, the two distinct ridden tolt speeds (slow tolt and fast tolt) were identified for each individual horse. Two experienced riders (body mass: 60kg, 62kg) were used to ride 4 horses each. At each speed the movement of the markers was documented in 3 measurement situations: without heel boots, with light-weight heel boots (1 70g) on both forelimbs, and with heavy heel boots (280g) on both forelimbs. The chronology of the resulting 6 measurement situations was randomized, and in each measurement situation two episodes of 20s were measured. This resulted in a minimum of twenty motion cycles available per situation for further analysis. For further analysis, the motion cycle duration was normalized to 100%, and the stance phases of all four limbs were used to calculate the overlap between the stance phases of all four limbs, the presence of 3 limb support phases. In order to indicate the type of gait diagonal and ipsilateral stance phases were compared, resulting in a value of 0 for clear pace pattern (with only ipsilateral stance phase overlaps), a value of 1 for ideal tolt and a value of 2 for typical trot (with only diagonal stance phase overlaps). Additionally, the angle between the frontal bone marker, the sacral bone marker and the horizontal was calculated, and the range of movement of this angle during motion cycles was used as an indicator of steady head carriage. Normal distribution of values was tested using the Kolmogoroff Smirnoff Test, and subsequent Student's t-tests for paired samples were carried out to test the significance of the differences found. Significance was defined for p values < 0.05. All 8 horses could be ridden on the treadmill and measured in the 6 measurement situations, with an average speed of (2.96±0.30m/s) for slow tolt and (4.10±0.32m/s) for fast tolt. Without heel boots, all horses showed a tolt pattern that was close to pace. As a group, and independent of heel boot placement, the horses showed a significantly higher tolt index in the fast tolt than in the slow tolt (p=0.04). For each of the individual horses, measurement situations could be identified, where the gait pattern was significantly closer to tolt than in other situations. Four of 8 horses showed the highest tolt index during the slow tolt with heavy heel boots - in one horse this index was similar to the slow tolt with light weight heel boots. Only one horse (Horse 1) in a single measurement situation (fast tolt, light weight heel boots) showed a gait pattern that was close to trot, in all other situations of all the horses the tolt was closer to pace than to trot. This study shows the besides tolt speed the placement of weigthed heel boots changed the gait pattern of tolt significantly in all horses, and produced the individual best tolt pattern in 6 of 8 horses during slow as well as in 6 of 8 horses during fast tolt. However, the direction of change is indvidual, and cannot be predicted from the gait pattern without heel boots. This should be taken into account during training, especially in Icelandic Horses with high forelimb action, where detrimental effects of peak accelerations of the distal limb may become relevant.