Modelling fore- and hindlimb peak vertical force differences in trotting horses using upper body kinematic asymmetry variables.

Abstract

Differences in peak vertical ground reaction forces (dFz) between contralateral forelimbs and hindlimbs are considered the gold standard for quantifying weight-bearing lameness. However, measuring kinematics for the same purpose is more common and practical. Vertical movement asymmetries (VMA) of the horse's upper body have previously been correlated to fore- and hindlimb lameness. But the combined response of head, withers and pelvis VMA to fore- and hindlimb dFzhas not yet been thoroughly investigated. Deriving the kinetic responses from kinematics would help the interpretation and understanding of quantified weight-bearing lameness. In this retrospective study, 103 horses with a wide range of fore- and hindlimb dFzhad been trotted on a force-measuring treadmill synchronized with an optical motion capture system. VMA of the head, withers and pelvis as well as dFzwere extracted. Multiple linear mixed models and linear regressions of kinematic variables were used to model the dFz. It was hypothesised that all included VMA would have a significant influence on the dFzoutcome variables. The results showed a complex relationship between VMA and dFzwhere both amplitude and timing of the VMA were of importance. On average, the contribution percentage of VMA to fore/hind dFzwere 66/34% for head, 76/24% for withers and 33/67% for pelvis. The linear regressions for the fore/hindlimb models achieved mean measurement root mean squared errors of 0.83%/0.82% dFz. These results might help determine the clinical relevance of upper body VMA and distinguish between primary fore, hind, ipsilateral and diagonal weight-bearing lameness.