Range of back movement at trot in horses without back pain

The aim of this study was to establish basic reference data for evaluating 3-dimensional movement of the equine back at the trot. In 22 mature horses without any clinical signs of back pain, the movement of the back was measured during trotting on a treadmill with a system for motion analysis. The position of the markers placed on the head, hooves, skin above the spinous processes of T5, T10, T16, L3 and on 2 of the sacral spines was recorded. The results of all movements were expressed in percent of the horse's height at its withers. At the trot, the maximum lateral movement at the head was 1.72% (s.d. 0.75). At T5 it was 3.15% (s.d. 0.84), at T10 1.99% (s.d. 0.64), at T16 1.85% (s.d. 0.65), at L3 1.89% (s.d. 0.62), at OS1 1.89% (s.d. 0.66) and at OS2 2.21% (s.d. 0.71). The maximum dorsoventral back movement was 4.06% (s.d. 1.14) at the head, 3.93% (s.d. 0.67) at T5, 4.46% (s.d. 0.85) at T10, 4.94% (s.d. 0.77) at T16, 4.91% (s.d. 0.74) at L3, 4.55% (s.d. 0.69) at OS1 and 4.33% (s.d. 0.69) at OS2. The lateral movement of the back at trot is relatively small compared to the movement of the horse's back at stance or at walk, with the marker on T5 showing the widest lateral movement. The dorsoventral movement of the back is larger than the lateral movement, but the differences between single markers are small. The results of this study can be used as a comparison when investigating equine back pain.