Synchronization dynamics between rider and saddle motion across gaits revealed by IMU analysis

Effective rider-horse coordination is essential for performance and welfare, yet objective, field-based quantification of rider-saddle synchronization across gaits remains limited.

To quantify dynamic synchronization between rider motion and saddle motion (as a proxy for horse trunk oscillations) across walk, trot, and canter using a minimal inertial measurement unit (IMU) setup, and to determine whether synchronization differs between rider body segments.

Two experienced riders (8-20 years riding experience) rode their own or familiar warmblood horses (n = 2; age 6-14 years) at walk, trot, and canter under collected, medium, and extended riding frame (collection level) conditions. Four wireless inertial measurement units (pelvis, trunk, head, saddle) recorded tri-axial acceleration at 60 Hz. Vertical acceleration of rider segments was analyzed relative to saddle motion. Synchronization was quantified using cross-correlation coefficients, phase lag, and phase-locking values (PLV). Mean values were calculated across repeated trials.

Synchronization strength increased with gait speed. Mean cross-correlation coefficients between pelvis and saddle were 0.64 at walk, 0.92 at trot, and 0.96 at canter, with corresponding mean phase lags of 22 ms, 0 ms, and 0 ms, respectively. Trunk and head segments showed lower synchronization at walk (r = 0.62-0.65) but high coupling at trot (r = 0.88-0.93) and canter (r = 0.91-0.95). Mean PLV values increased from 0.52 to 0.55 at walk to 0.91-0.95 at trot and 0.92-0.94 at canter. Riding frame condition influenced synchronization primarily at walk, with lower mean correlation and PLV in the extended frame.

Within this population, rider-saddle synchronization increased with gait speed and was strongest at the pelvis, supporting its role as the primary mechanical interface transmitting horse trunk motion to the rider. A minimal IMU-based approach captured repeatable, segment-specific synchronization patterns under field conditions.