In horseback riding, the physical influence of the rider is increasingly being recognized as an important contributor to equine back pain. Asymmetrical loading, in particular, can be detrimental to performance. The aim of this study was to investigate the left-to-right differences in mean pressure distribution, and other parameters, on the equine back at Week 0 and Week 8 of an unmounted equestrian core fitness program. Ten healthy dressage horse and rider pairs (horse age 12.30 ± 4.64 years, rider age 41.5 ± 14.83 years) performed two ridden tests at sitting trot, before and after participating in an 8-week program. The regime was a sport-specific, 20-minute core fitness program, performed three times weekly. Horses and riders each wore four reflective markers. A Pliance™ electronic saddle mat (60Hz sampling rate) and Casio™ high speed camera (240 frames per second) with Quintic™ biomechanical software were used to record all trials. All subjects (n=10) showed a significant decrease in left-right mean pressure differential of 0.368 ± 0.361kPa. Maximum overall force (F = ma) had a non-significant increase of 2.36 ± 3.36N/kg (p=0.05), normalized to rider body mass. Mean stride length (m) increased by 8.4%. This study demonstrates that participating in a rider core fitness program can have a significant effect on rider symmetry and consequently provide an important method for reducing asymmetrical loading and improving both human and equine performance.