8. Your horse is strangely asymmetrical (or too symmetrical) trotting a circle.
We know a lame horse often looks lamer when trotting in a circle. But what a rider feels can vary considerably, depending on the direction, the way he or she rides the trot, the location of the lame limb(s), and the kind of lameness. In fact, in some combinations of those variables, a lame horse can look even more symmetrical than a sound horse, says Rhodin, based on work she did with PhD student Emma Persson-Sjodin.
“When you’re posting a trot, you’re loading one hind limb in the sit phase, causing asymmetry,” she says. “When you’re trotting in a circle, the forces of the circle also cause the horse asymmetry. And so does lameness. So you can either exacerbate that lameness or cancel it out completely.”
Her biomechanics team induced temporary subtle lameness in sound study horses. They analyzed the effect of trotting on a circle on movement asymmetry. The circle induced asymmetry in sound horses and increased or decreased the degree of lameness, depending on whether the lame limb was to the inside or outside of the circle. Then they studied the effect of different riders’ seats in various combinations of directions, circles, and lameness types.
One of the things they noted was a significant difference in the way horses move, depending on whether they have “impact” (foot landing) or “push-off” (foot leaving the ground) pain.
If the rider sits when the sound limb hits the ground in impact hind-limb lameness, the asymmetry gets worse. That asymmetry is further exacerbated if the lame limb is on the inside of the circle. The opposite might be true if the horse has push-off pain, Rhodin says.
Meanwhile, if the rider is sitting when the impact-lame hind limb hits the ground, the asymmetry evens out. If the lame limb is on the outside of the circle and the rider posts the trot on the incorrect diagonal, the asymmetry might cancel out completely. In extreme cases the horse could become asymmetrical in the opposite direction.
“Lame horses can actually feel very even, depending on the various combinations of forces under rider and in a circle,” Rhodin says. “It’s important to be aware of the different factors involved. Otherwise, it’s too easy to just say, ‘Oh look, he’s fine after all!’ ”
Dyson adds that irrespective of which rein you are on, if you switch diagonals the horse should feel the same. “If it does not feel the same or if the horse preferentially throws you on to one diagonal, that is not normal,” she says.