Differences in rider movement pattern between different degrees of collection at the trot in high-level dressage horses ridden on a treadmill

Both at higher speed in collected trot and in passage, the rider's pelvis became more caudally rotated and the rider's lumbar back became more flexed. However, in passage there was also a decrease in phase-shift between horse and rider movements, suggesting that the rider used the seat more actively. In free trot, the rider's pelvis was more cranially rotated, the lumbar back was more extended, the rider's body inclined more forwards, and the phase-shift between horse and rider was increased, compared to collected trot. The observed changes were partly explainable from changes in the horse's movement pattern. However, most differences in rider body position seemed unrelated to the horse's movements, but were in accordance with instructions in equestrian texts, suggesting that those changes were voluntarily adopted by the riders.