The effect of horseshoes and surfaces on horse and jockey centre of mass displacements at gallop

Abstract

Horseshoes influence how horses’ hooves interact with different ground surfaces, during the impact, loading and push-off phases of a stride cycle. Consequently, they impact on the biomechanics of horses’ proximal limb segments and upper body. By implication, different shoe and surface combinations could drive changes in the magnitude and stability of movement patterns in horse-jockey dyads. This study aimed to quantify centre of mass (COM) displacements in horse-jockey dyads galloping on turf and artificial tracks in four shoeing conditions: 1) aluminium; 2) barefoot; 3) GluShu; and 4) steel. Thirteen retired racehorses and two jockeys at the British Racing School were recruited for this intervention study. Tri-axial acceleration data were collected close to the COM for the horse (girth) and jockey (kidney-belt), using iPhones (Apple Inc.) equipped with an iOS app (SensorLog, sample rate = 50 Hz). Shoe-surface combinations were tested in a randomized order and horse-jockey pairings remained constant. Tri-axial acceleration data from gallop runs were filtered using bandpass Butterworth filters with cut-off frequencies of 15 Hz and 1 Hz, then integrated for displacement using Matlab. Peak displacement was assessed in both directions (positive ‘maxima’, negative ‘minima’) along the cranio-caudal (CC, positive = forwards), medio-lateral (ML, positive = right) and dorso-ventral (DV, positive = up) axes for all strides with frequency ≥2 Hz (mean = 2.06 Hz). Linear mixed-models determined whether surfaces, shoes or shoe-surface interactions (fixed factors) significantly affected the displacement patterns observed, with day, run and horse-jockey pairs included as random factors; significance was set at p<0.05. Data indicated that surface-type significantly affected peak COM displacements in all directions for the horse (p<0.0005) and for all directions (p≤0.008) but forwards in the jockey. The largest differences were observed in the DV-axis, with an additional 5.7 mm and 2.5 mm of downwards displacement for the horse and jockey, respectively, on the artificial surface. Shoeing condition significantly affected all displacement parameters except ML-axis minima for the horse (p≤0.007), and all displacement parameters for the jockey (p<0.0005). Absolute differences were again largest vertically, with notable similarities amongst displacements from barefoot and aluminium trials compared to GluShu and steel. Shoe-surface interactions affected all but CC-axis minima for the jockey (p≤0.002), but only the ML-axis minima and maxima and DV-axis maxima for the horse (p≤0.008). The results support the idea that hoof-surface interface interventions can significantly affect horse and jockey upper-body displacements. Greater sink of hooves on impact, combined with increased push-off during the propulsive phase, could explain the higher vertical displacements on the artificial track. Variations in distal limb mass associated with shoe-type may drive compensatory COM displacements to minimize the energetic cost of movement. The artificial surface and steel shoes provoked the least CC-axis movement of the jockey, so may promote greatest stability. However, differences between horse and jockey mean displacements indicated DV-axis and CC-axis offsets with compensatory increases and decreases, suggesting the dyad might operate within displacement limits to maintain stability. Further work is needed to relate COM displacements to hoof kinematics and to determine whether there is an optimum configuration of COM displacement to optimise performance and minimise injury.

Hoof Impact and Foot-off Accelerations in Galloping Thoroughbred Racehorses Trialling Eight Shoe-Surface Combinations

“…Nevertheless, at gallop when the accelerations and loads are amplified, even small differences could be relevant for injuries and safety. In fact, the findings here tie in with the horse and jockey centre of mass displacements, which indicated that the largest vertical displacement differences were present between barefoot-artificial and steel-turf [85]. This suggests that hoof kinematic patterns are translated into upper body kinematics.…”

“…In addition, previous comparisons between contralateral and ipsilateral pairs of limbs found that the leading forelimb and non-leading hindlimb were at greater risk [41]. Data from this study suggest the leading limbs experience the largest accelerations on the tracks used here, which had only a very slight anticlockwise bend [85]. Based on EMMs for surface effects (Table 3) averaged across all acceleration axes, the leading limbs had accelerations that were 1.5 times larger than the non-leading limbs.…”

“…The maximum absolute differences occurred in the leading forelimb between surfaces for z-maximum and y-maximum (difference of 12.6 g and 10.4 g, respectively), which may reflect the fact that in this limb the braking and vertical impulses must decelerate the centre of mass and provide it with sufficient upward vertical velocity for the flight phase of the stride [95]. Vertical centre of mass displacements are indeed larger by around 5.7 mm downwards and 2.5 mm upwards on the artificial surface as a result of this action [85]. The general trend toward higher hoof accelerations on the artificial surface (Table 3) is also consistent with a faster breakover on this surface [28].…”

“…Scatter plots were used to investigate whether the hoof acceleration patterns were correlated with the tri-axial centre of mass displacements of the horses reported previously [85] and these are included as supplementary information in Figure S3. In summary, weak to moderate correlations were found between the tri-axial hoof impact acceleration parameters and the tri-axial centre of mass displacements.…”

“…Further work is needed to establish the collective impact of shoes and surfaces on racehorse gait kinematics and kinetics, including the accelerations and loads experienced. In particular, it is worth noting that alterations to hoof motion appear to be reflected in the upper body movements of horses and their jockeys [85]. Hence, understanding the controls on the hoof-surface interaction in greater detail is likely to have implications for the likelihood of jockey injury and falls.…”