Saddle Science: Tree Width's Effect on Horses' Thoracic Spines
Saddle fit has historically been an art rather than a science, with little research to support what constitutes good fit. One area lacking objective evidence is the effect of saddle width on horses’ backs. Russell MacKechnie-Guire, of Centaur Biomechanics and The Royal Veterinary College, in Hatfield, U.K., recently conducted a study to evaluate just this. He presented his findings at the 2019 British Equine Veterinary Association Congress, held Sept. 11-14 in Birmingham, U.K.

“There is a notion in the industry that fitting saddles too wide will allow the thoracolumbar region (the part of the spine that runs from the horse’s withers to his pelvis) to increase its range of motion and improve muscular function, but none of this is supported by scientific evidence,” he began.

In his current study, he aimed to evaluate the effect of three different saddle widths (correct, narrow, and wide) on thoracolumbar kinematics (movement) in horses ridden at the canter, a gait at which this part of the spine has increased range of motion.

His team fitted 13 sound horses housed at the same facility with a validated sensor system and glued inertial measuring units along each horse’s poll; withers; 13th (T13) and 18th (T18) thoracic vertebrae; third lumbar (L3); sacrum; and left and right tuber coxae (LTC, RTC). They collected data as two similar-sized, right-handed female riders rode each horse in a properly fitted, general-purpose Kent & Masters English saddle. MacKechnie-Guire said they chose this type of saddle because of the adjustability of the tree width.

“We tested three conditions: correct tree width as determined by five Society of Master Saddlers Qualified Saddle Fitters, one fitting narrower, and one fitting wider,” he said. “This equated to a 10-degree difference based on the British standard for saddle trees.”

During the exercise tests, each rider warmed up at the walk, trot, and canter in both directions for 15 minutes before cantering through a calibrated track on both reins. The footing was groomed between horses, and the riders and researchers were blinded to each saddle tree width.

MacKechnie-Guire measured three kinematic factors of the thoracolumbar spine at the canter:

  1. Flexion and extension. Horses wearing the wide saddle had significantly less flexion and extension at T18 compared to the correct saddle.
  2. Axial rotation. Horses wearing the wide saddle had significantly more axial rotation at the withers and significantly less axial rotation at T13 and L3.
  3. Lateral bending. The narrow saddle reduced lateral bending at T18.

In summary, both the wide and narrow saddles reduce thoracolumbar range of motion, MacKechnie-Guire said, riding in saddles that are too narrow or too wide likely affect thoracolumbar kinematics due to the instability and positioning of the saddle and rider.

“Correct saddle width and fit is essential to promote unhindered back function,” he concluded. “Tree width has an effect on equine locomotion, saddle pressures, and thoracolumbar dimensions in the canter.”