Ground schooling (especially lunging) is routinely performed in the rehabilitation and training of horses. Training rollers are commonly used to provide attachment for training aids. The objective of the study was to objectively measure pressures beneath a training roller during lunging exercise with and without a Pessoa training aid. To measure pressures underneath the roller; 10 nonlame horses (mean ± standard deviation [SD] age 12 ± 8.77 years, mean ± SD height 1.65 ± 0.94 m) were lunged on a 16-m circle wearing a training roller on top of a high withered dressage square and wool pad. A Pliance (Novel) pressure mat was positioned transversely over the spinous processes covering thoracic vertebrae 10 to 15. Data were collected in both trot and canter on the left and right reins, with and without a Pessoa training aid. For pelvic range of motion (ROM), horses were instrumented with five inertial measuring unit sensors (IMU). A paired t-test was used to determine differences in pressure and pelvic ROM with/without Pessoa training aid (P ≤ .05). In trot and canter, consistent high pressures on the spinous processes beneath the roller were greater than those thought to cause back discomfort. These pressures were consistent between horses. No significant differences were found in any IMU outcome parameters. An awareness of the increased local spinal pressure a training roller exerts on the back, especially in horses undergoing rehabilitation of back problems is needed.