A Possible Solution for Muscle Imbalance

Recently, a team of scientists set out to discover new ways to improve equine imbalances.

A team of scientists improved their research horses’ imbalances by attaching a neoprene bell boot on the horses’ hind feet when being ridden. The boots stimulated the sensory receptors on the horses’ pasterns, encouraging more muscle activity. Photo: Emily Daily

Most riders have felt their horses “go better” in one direction than the other. Maybe he feels stiff to the left or never drives equally from his hind legs. These imbalances may be caused by a number of factors, including injury, poor nutrition and neurologic issues. Over time, they can lead to soft-tissue strains and outright lameness. Thus, correcting an imbalance can be important to keeping your horse sound.

Research shows that stimulating sensory receptors in the skin of a horse’s pastern on the imbalanced limb (the one that is less active or less engaged) could be therapeutic. In fact, this kind of light stimulation may change the horse’s muscle activity, improving postural control and even helping to restore balance and normal movement.

A team of researchers at Copenhagen University in Denmark, led by Adrian P. Harrison, IVH, wanted to follow up on this concept. They selected eight healthy dressage horses, aged 6 to 15, with no history of lameness. They evaluated each horse’s muscle function at walk, trot and canter on 20-meter circles to the left and right, watching the action of the superficial gluteal muscle. Located in the horse’s hindquarters, this muscle controls hip extension and outward rotation of the limb.

The evaluations showed a significant difference in muscle activity between the left and right hind limb for each horses at all three gaits on the left-hand circle. The left hind was seen as the weaker limb.

The horses were then started on a six-week rehabilitation program to see if the asymmetry could be corrected. Every third day during the trial period, each horse wore a lightweight neoprene bell boot on the left hind leg. The horses’ owners rode them for 60 minutes, following their regular exercise routine. Researchers theorized that the bell boot would provide light stimulation to the sensory receptors, which would then alter muscle activity to help correct the muscle imbalance.

The same evaluations were repeated at the end of the study. Researchers saw a significant improvement in each horse’s imbalance, with the left hind showing greater engagement at all three gaits on the left-hand circle. Analyzing recordings of muscle contractions showed that the change was due to more intense muscle-fiber activity. The researchers concluded this was caused by the bell boot stimulating the sensory receptors.

Interestingly, only non-significant imbalances were found during the initial evaluations on the right-hand circle. After the trial period, the horses showed slight improvements at walk and trot on the right-hand circle, but increased imbalance at the canter. Researchers speculated that this could be the result of the horses overcompensating on, and thus stressing, the right hind when the left hind wore the bell boot. This indicates that while the technique shows promise, further investigation is warranted. 

This article was originally published in the October 2018 issue of Practical Horseman. 

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