Hydrotherapy to Rehabilitate and Condition Horses
What researchers and veterinarians are discovering about equine aquatic conditioning and rehab
Veterinarians have been using swimming, underwater treadmill work, and other forms of hydrotherapy in equine rehabilitation and conditioning protocols for years. Historically, they’ve based their recommendations largely on anecdotal evidence and personal experience. While questions remain, in recent years researchers have learned a significant amount about how aquatic therapy benefits horses.
Aquatic Exercise 101
Swimming pools, underwater treadmills, cold-water spas, and even beaches are gaining popularity as equine conditioning and rehab tools.
“The main benefit of exercise in water, whether that’s walking on a water treadmill or swimming in a pool or open water, is the ability to exercise the horse with reduced loading or concussive forces,” says Persephone McCrae, PhD, who studied water treadmill use in horses for her doctoral degree. “Musculoskeletal injuries are typically associated with repetitive overloading of the structures within the limb,” and buoyancy limits these forces.
And, she adds, because water is denser than air, horses must work harder at slower speeds during aquatic exercise, leading to improved cardiorespiratory fitness and muscle development.
The reduction in weight-bearing also promotes range of motion, or flexibility, through the limbs and back, says McCrae, now the lead scientist for research and development in the Animal Science Division at Myant Inc., a textile computing company in Ontario, Canada. “This is important in terms of reducing the risk of future injury, as well as for promoting rehabilitation through improved biomechanics, even while the horse may not be fully weight-bearing on ground.”
As for drawbacks, there are a few: Horses must acclimate to aquatic modalities, which can take time, and even after training some don’t take to it well.
Further, hydrotherapy isn’t a magic bullet for rehabbing all issues. “There are cases (for which) aquatic training is not advised, particularly when lacerations or abrasions of the skin are involved, as this may place the horse at risk of developing an infection,” McCrae says. “There are also concerns associated with long durations spent in water, especially for the integrity of the hoof.”
The reduced skeletal loading that’s so advantageous for healing also results in decreased stimulus for bone to become strong. So, while the muscular and cardiovascular systems might gain conditioning, the skeletal system does not, or it might even become weaker if the horse is on stall rest.
And, like any exercise, aquatic conditioning has the potential to be damaging if not used correctly and carefully.
“If a horse is not fit for aquatic treadmill exercise, if they are pushed too hard, or if a protocol is determined without reasoning, it may be possible to cause injury,” says Brittany Silvers, PhD student and graduate research assistant in Texas A&M University’s Department of Animal Science, in College Station.
McCrae agrees. “It is essential that users tailor their protocols and monitor horses during aquatic exercise, paying close attention to perceived effort and biomechanics, to ensure that the duration, speed, and water height (depth) are appropriate for the specific condition and for the desired outcomes,” she says.
Researchers have conducted few longitudinal studies—in which they assess the same horses over time—involving water treadmills or other aquatic exercise, making it difficult to develop scientifically backed protocols, says Silvers. Here are recent findings and advancements, however, that might help improve our understanding of how water exercise benefits both healthy and rehabbing horses.
McCrae and colleagues performed a study in 2019 exploring how water level and treadmill speed affect forelimb loading. “Every time the hoof makes impact with the ground, shock must be absorbed by the structures within the limb, a large percentage of which occurs within the hoof,” she says.
This repetitive loading could lead to cartilage breakdown and joint degradation.
“By having horses exercise in water at the stifle level, we were able to reduce the amount of shock experienced by the hoof by approximately 30%,” McCrae says.
In a 2021 study McCrae and colleagues showed that carpal and fetlock range of motion (ROM) were significantly smaller during swimming than during flexion on the ground, but elbow range of motion was the same. They believe this is because there’s no weight-bearing phase during swimming to cause extension of the lower joints.
“For horses stagnating during the rehabilitation of an injury and showing pain or avoidance/defensive behavior during passive flexion/extension of a given joint, the introduction of swimming exercise may help to regain some ROM in a safe way,” the team noted.
They also found that all three joints’ absolute angular velocities were greater during retraction than protraction (which corresponds to the swing phase of the stride on ground). The team said water resistance could be a contributing factor and lead to fatigue earlier than overground exercise.
In 2013 researchers in the Netherlands and Belgium found that treadmill water level impacted how horses’ backs move at the walk. They concluded that increasing water depth resulted in more back flexion and rotation but reduced lateral bending at the highest water levels. And, they added, after 10 days of water treadmill work, horses showed more back flexion.
Additionally, researchers from the Hartpury College Equine Therapy Center, in the U.K., showed that walking in deep water on a treadmill resulted in significantly increased cranial thoracic extension (lengthening of the neck and back) and thoracolumbar flexion (over the mid-back) than did walking in water at hoof depth.
Veterinarians might consider these findings when designing conditioning and rehab programs for horses with spinal pathology.
Colorado State University researchers tested the effects of underwater treadmill work on horses with experimentally induced carpal osteoarthritis. Compared to horses that walked on a dry treadmill, horses that walked on an underwater treadmill had reduced synovial membrane inflammation, which led to better clinical improvement.
“Overall improvements in thoracic limb function, joint range of motion, and synovial membrane integrity indicated that exercise in an underwater treadmill was a potentially viable therapeutic option for the management of carpal joint osteoarthritis in horses,” the team reported.
In a previous study CSU researchers revealed that underwater treadmill exercise significantly improved postural stability, which they said provided evidence-based support for aquatic exercise.
An international research team recently found that Thoroughbred racehorses rehabbed on an underwater treadmill returned to racing earlier after carpal or fetlock chip surgery than counterparts rehabbed on a dry treadmill. Overall, 83% and 61% of horses rehabbed on the aquatic and dry treadmills, respectively, returned to racing, leading the team to conclude that underwater treadmills were superior for rehabbing Thoroughbreds after arthroscopic surgery.
Additional research will help veterinarians fine-tune how they incorporate aquatic exercise into a typical land-based conditioning program to rehab specific injuries.
Use in Healthy Horses
Water treadmills and oxygen consumption
McCrae and colleagues looked at how an 18-day dry treadmill or stifle-height water treadmill conditioning program affected unfit Thoroughbreds. Horses’ peak oxygen consumption increased significantly (by 16.1%) following water treadmill work but did not increase after dry treadmill work. This led them to conclude that water treadmill work can significantly improve fitness without the stresses that can accompany traditional overground exercise.
Underwater treadmills, cartilage, and bone metabolism
Silvers and colleagues recently assessed aquatic exercise’s impacts on bone and joint health in young, growing horses turned out for 10 hours a day compared to similar exercise on dry land. Due to buoyancy, she says, “there’s concern that horses on the aquatic treadmill may have decreased loading and, therefore, decreased bone development, which would be problematic for horses at a young age undergoing such an important time in bone maturation.”
However, they didn’t observe differences in bone parameters for yearlings exercised on aquatic versus dry treadmills, she says, suggesting no negative impact of aquatic treadmill exercise on bone development, so long as horses have access to high-speed exercise—either forced or during turnout.
Water treadmill best practices
Based on research, personal experiences, and discussions, Kathryn Nankervis, PhD, McCrae, and colleagues published Equine Water Treadmill Exercise—A Guide for Users, in 2020 (available at bit.ly/34rnidp), and a 2021 consensus statement on water treadmill use in healthy horses in the journal Animals.
“As a result of our discussions, it is apparent that there is much work to be carried out before broad agreement, based on evidence, could be reached regarding the most appropriate application of water treadmill exercise for the rehabilitation and ongoing management of horses with specific orthopedic injuries,” the group said in the statement. “However, by sharing experiences, both positive and negative, practitioners can inform the development of research questions, and research findings can be disseminated directly to users, with benefits for equine welfare and better recovery from injury.”
“Aquatic exercise is a great tool for veterinarians to have in their toolkit, whether for conditioning or for rehabilitation,” McCrae says. “It works especially well to complement other forms of exercise and therapies to promote performance and recovery.”
She and Silvers encourage practitioners to be adaptive when implementing water exercise.
“Each horse and their needs will be completely individual and, therefore, the training protocol should be tailored specifically to that horse,” Silvers says. “There is no one-size-fits-all program that will cause identical results for every horse.”
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