The effect of repeated shocks on the low back during horse riding

Repeated shocks, such as those occurring during horse riding, may result in a risk of overloading the low back. This study investigated accelerations and angular changes in the low back during horse riding, using Inertial measurement units (IMUs) on the pelvis, and L4, L1, and T11 spine levels during 30 min of walking and 10 min of cantering in twelve female participants. The root mean squared (RMS) linear acceleration of each IMU and the transmission (signal transfer) between each pair of IMUs were calculated from the measured accelerations. Additionally, angular motions between IMU's were quantified. The RMS of vertical pelvis accelerations was overall higher for cantering than for walking, with a peak value of 5.52 vs. 0.85 m/s² at 1.8 Hz. Transmission of accelerations was 1 or slightly above 1 at 4 Hz, indicating pelvis accelerations to be passed on to the low back equally or somewhat amplified. Above 4 Hz, accelerations were damped, increasingly so with increasing frequency. Damping was the largest between the lowest segments. Rapid (<0.1 s) and relatively large (up to 30°) angular changes were found between the Pelvis and L4 sensors. High-frequency angular movements indicate involuntary movements, likely as a result of impact. Potentially, angular changes and spine compression resulting from the accelerations during shock loading in horse riding could exceed injury thresholds.