Equestrian sports report three to five times higher incidence rates for lower back pain than that of the general population, with hip flexion angles of 50-60° suggested as a causal factor. Inertial motion capture technology enables dynamic measurement of rider kinematics but data extraction is time-consuming. The aim of this study was to develop a software tool to automate the process of extracting biomechanical data from the Xsens™ MVN (MoCap) system to investigate postural changes in riders, comparing static position at halt with dynamic position during the sit phase of rising trot. The software was found to be efficient, reducing data extraction time by 97% when used with a sample of 16 riders. Good correlation was found between hip flexion and pelvic anterior-posterior rotation and between halt and trot but with significantly greater values of hip flexion and pelvic anterior rotation in trot. No riders showed hip flexion >50° at halt but 11 riders (69%) showed hip flexion >50° during the sit phase of rising trot, indicating that dynamic assessment is important when considering rider postural faults that may put them at risk of back injury.