Muscle asymmetry in the thoracic region has implications for saddle fitting. If the muscle on one side of the withers is more developed than the other, this will affect saddle fit, potentially causing pain and discomfort.
A study, led by assistant professor Dr. Katrina Merkies, at the University of Guelph, Ontario, Canada looked at muscular symmetry at the withers.
Undergraduate students in the Department of Animal Biosciences, Julia Alebrand, Bethany Harwood, Katharine Labarge and Laura Scott conducted a retrospective study of 490 horses. They studied withers measurements, taken with a flexible withers tracing tool, that had been recorded by a saddle fitting company.
Horses of various breeds (from Arabs and Thoroughbreds to stocky Warmbloods and Drafts) and a range of disciplines (dressage, hunter/jumper, recreational pursuits) were included in the study.
They found that almost 60% of horses had more muscle on the left side.
In this population of horses, wither measurements were not significantly affected by horse breed, age, sex, height or level of training. Rider age, gender, height, weight and level of training did not affect wither measurements either.
The work is reported in Comparative Exercise Physiology. The authors report that horses in their study were asymmetric in their thoracic structure with most being larger on their left side than the right. They suggest that this asymmetry may be due to genetics, environment, or training. Importantly, it should be considered when fitting a saddle to the horse.
For more details see:
Investigation into thoracic asymmetry in ridden horses
K. Merkies; J. Alebrand; B. Harwood; K. LaBarge; L. Scott.
Comparative Exercise Physiology (2020), Vol 16, 1, pp. 55-62(8)
To find out more about the study, watch a video interview with Dr. Merkies