Optimal interval for periodical lead limb changes during straight gallop in race horses

In transverse gallop the leading feet (i.e. the second limb of each pair on the ground) of hind and forelimbs are ipsilateral. Therefore, we can distinguish a right-leading by a left-leading gallop. When turning, a horse leads with its inside limbs. Consequently, during direction changes, right-hand bends are covered using right-leading gallop and vice-versa. Even if there are preferences for the leading foot on straights, probably due to individual asymmetries of the body, we also observe periodical lead changes. Potential reasons for those are: a) the interaction between the shoulder and the thoraco-pulmonar complex, which is maximum during the lead leg support, and b) musculo-skeletal stress induced by the gait asymmetry (the trunk sagittal plane deviated from the progression plane by 3º, pers. obs.). Also by considering that the lead change discontinuity on straights is expected to decrease gallop performance, we hypothesized that there should be a consistently “optimal” number of strides or distance between lead changes. From the analysis of 84 horse-race videos of different tracks in Italy, we found that 48 ± 20 strides were covered between two successive lead changes on straights. As expected, race distance, the number of bends to be covered and, possibly, the 'rider-factor' influenced the number of changes. The predominant leading leg used on straightaways is significantly different from that employed during bends in both clockwise and counter-clockwise racetracks.