Hydrotherapy in Canine Physical Rehab

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The role of therapy pools and underwater treadmills in physical rehabilitation, and what to consider when adding these to your facility.

Hydrotherapy, or aquatic therapy, has become an important part of physical rehabilitation for dogs. The aim is to return the patient to full function following injury, manage long-term medical conditions, and improve fitness. Both therapy pools and underwater treadmills (UWTM) are used by canine rehabilitation professionals to achieve these goals.

Properties of water

When planning an aquatic rehabilitation program, it is necessary to understand the basic properties of water, including relative density, buoyancy, viscosity, resistance, hydrostatic pressure and surface tension, as they relate to rehabilitation.1

Relative density

Relative density or specific gravity is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material — usually water. The specific gravity or relative density of a canine patient varies with body composition, with lean muscle having a lower specific gravity and fat having a higher specific gravity. Objects with a specific gravity lower than 1 (the specific gravity of water) will sink, while those with a higher specific gravity will float. A lean animal that is not moving in the water will sink, while an obese animal will tend to float. This principle needs to be remembered when doing aquatic therapy, since the deeper the water, the less weight is being carried on the limbs.2


Buoyancy is defined as “the upward thrust of water acting on a body that creates an apparent decrease in the weight of a body while immersed”. This is Archimedes’ principle, which states that if a body is fully or partially submerged in a fluid, it experiences an upward thrust equal to the weight of the fluid displaced. The buoyancy of water aids in the rehabilitation of weak muscles and painful joints. It allows the patient to stand and exercise while minimizing weight-bearing on sore joints. If a dog is immersed in water to mid-chest, his joints are bearing only 38% of the weight they would on dry land. With less load on painful joints, the dog is able to exercise more comfortably. Research on women who exercised in a pool in waist-deep water three times a week showed an 18% increase in muscle strengthening and functional fitness. Range of motion (ROM) and muscle strength were both improved in this group while minimizing damage to soft tissue structures.2


Water’s viscosity also provides resistance to movement. Viscosity is defined as a “measure of the frictional resistance caused by cohesive or attractive forces between molecules in a liquid”. The viscosity of water makes it more difficult for the animal to move through water than through air. This resistance is used to strengthen muscles and improve fitness. Along with the property of buoyancy, the viscosity of the water provides support for unstable joints. A paralyzed dog, for example, is more willing to walk in water than on land because the water holds him up and prevents falling. This greatly reduces the patient’s anxiety about exercise. If a patient is quite weak, he is able to move more comfortably in water than on land.  The resistance of the water allows him to get a more intense workout in a shorter period of time.2

Hydrostatic pressure

When a dog is immersed in water, the water exerts pressure on all parts of the animal. Hydrostatic pressure (the pressure of water) follows Pascal’s principle (a pressure change in one part is transmitted without loss to every portion of the fluid). This pressure is exerted constantly while the dog is in the water, providing a superior environment for the treatment of swollen joints or limbs and other edematous tissue. Not only does the water pressure reduce edema, but it also provides stimulation to skin afferent sensory receptors and reduces surface nociceptor activity. This type of stimulation decreases the animal’s pain perception and allows him to exercise with considerably less discomfort.2

Surface tension

Surface tension is defined as the mutually-attractive force of water molecules at the surface of the water. Water molecules are more tightly adhered to each other at the surface than underneath the water. At the surface of the water, therefore, there is a higher resistance to movement. It takes more energy to break the limb free of the water. The therapist can take advantage of this principle by varying the water in an underwater treadmill.2

Benefits of hydrotherapy

Exercising in water has many benefits. It improves strength and muscular endurance, cardiovascular fitness, range of motion, and well-being. Most dogs find water exercise, particularly swimming, to be fun! Dogs recovering from anterior cruciate surgery, fractures, neurological conditions, tendon or ligament injuries benefit greatly from aquatic therapy as part of their rehabilitation. Overweight, arthritic and senior dogs, and those with hip dysplasia or spondylosis, are also good candidates. Aquatic therapy engages muscles that are difficult to recruit with land exercises alone. It is less strenuous for the patient as it does not cause concussive forces on injured joints. Even dogs that do not suffer from any of these diseases can benefit from the increased level of fitness that aquatic therapy provides. Swimming or hydro treadmill sessions are often added to the conditioning regimes of canine athletes in the off season, in order to maintain appropriate cardiovascular fitness.3

Precautions to keep in mind

Some precautions need to be taken before instituting a hydrotherapy program. Dogs with open wounds or sores, and those that have breathing difficulties or heart disease, are not candidates for aquatic therapy. Additionally, if a dog panics in water, aquatic therapy may not be right for him; he may injure himself thrashing in the water.  Lifejackets, swim buddies, and competent aquatic therapists may be able to help such a dog get used to swimming. Alternatively, the underwater treadmill may be a better choice. The therapist must determine the dog’s fitness level as swimming in particular can be very strenuous.  After surgery, a dog may only be able to swim or walk in an underwater treadmill for a short period, due to fatigue.4

Hydrotherapy equipment

Although rehabilitation can be done effectively without hydrotherapy, clients have an expectation that a rehabilitation practice will offer hydrotherapy. Most small animal practices with rehabilitation services will offer an underwater treadmill, pool sessions or sometimes both.

Successful marketing of a hydrotherapy program can accelerate the growth of a clinic’s rehabilitation service. This marketing should be aimed at the general public as well as veterinary surgeons within a certain geographic radius. Investing in equipment such as underwater cameras and video are critical; it allows for the documentation of a patient’s progress, which can be easily shared on the clinic’s social media page.2,4 A comparison of the benefits of swimming and underwater treadmills are summarized in the table below.

Pools can either be custom built or prefabricated “drop in” models. They come in a variety of sizes and can be completed with decking for easy access. Pool jets can be added to increase resistance and therefore the work done by the patient. Disadvantages to swim therapy include the expense of installation, the space required to house the pool and associated pumps and equipment, and the costly water quality and air quality equipment needed to ensure the comfort and safety of both dogs and therapists. Daily costs of heating and maintaining the pool also need to be considered.

Several companies now market underwater treadmills, so you can explore the options before choosing a brand. All underwater treadmills should have an entrance and exit door, a reservoir tank for water, a heater and filter. Some of the extra options available with these units include incline/decline, and therapy jets. Other useful equipment includes either a mirror or camera with a projection screen, so the therapist can visualize the patient’s gait while she is in the treadmill. A treadmill-specific bench is also a good piece of equipment to have, since with neurological patients, the therapist often has to assist with gait patterning. Life jackets, harnesses, slings, head wraps, leg weights, pool noodles and toys are essential for hydrotherapy.2,4 See below for a list of features to look for when purchasing an underwater treadmill.

Underwater treadmills are complicated and expensive pieces of equipment that need to be properly maintained. Daily maintenance and cleaning protocols need to be put in place to ensure the machine continues to run efficiently. Before purchasing, talk to other rehabilitation professionals in your area to gauge the service availability for each particular treadmill, and what problems they have encountered. Even if the manufacturer offers stellar service, it is a good idea to have an ongoing relationship with a local pool company with maintenance people who can assist in the event of a plumbing issue or pump failure.

What to look for when purchasing an underwater treadmill

  • Long enough belt for patients expected
  • Incline or decline
  • All glass in and out doors and large viewing windows
  • Programmable
  • Slowest speed 0.1 mph
  • Jet for resistance
  • Hooks to allow attachment of slings for neurological patients
  • Wide enough to allow a therapist in with every patient
  • Quick release for ease of cleaning
  • Displays time, speed and distance
  • Good reliable company to help with training, onsite service and maintenance.

Individualizing patient protocols

With any rehabilitation patient, the therapist and dog owner must develop specific goals for recovery. Underwater treadmill and swim therapy both involve interval training with frequency of exercise, length of exercise session, and how many repetitions occur in each session. These parameters will change as the patient progresses through therapy.

Protocols for canine athletes will vary depending on the owner’s goal and the level of fitness that needs to be maintained. Varying resistance with jets, incline or decline, the height of water and speed of activity will be needed to challenge these patients.3

Maximizing revenue with hydrotherapy

Running a pool or underwater treadmill is associated with significant costs, which means income should be maximized for a good return on investment. Assuring your aquatic therapy is delivered at a time convenient for clients is key. Offering early or late appointments and weekend sessions may be necessary. Setting up obesity clinics for overweight pets, or conditioning clinics for canine athletes, may be another way to maximize investment. Introducing puppy swims along with puppy training classes is another way to showcase your facility. Having prepaid packages that clients can purchase for any type of hydrotherapy is another good marketing strategy. See below for ideas on revenue generation with an underwater treadmill.

Ideas for generating revenue with an underwater treadmill

  1. Obesity clinics for weight loss, for geriatric dogs in particular
  2. Packages including underwater treadmill for rehab clients
  3. Packages for spa days
  4. Packages for fun swims
  5. Conditioning packages for canine athletes
  6. Get referrals from other practices and social media for rehab or wellness care

Aquatic therapy has many benefits for our canine rehabilitation patients. Scientific research into aquatic therapy as applied to humans has revolutionized sports medicine; and as more canine research is forthcoming, further benefits of aquatic therapy will become apparent.

Author:  Janice Huntingford, DVM, DACVSMR, CVA, CVPP, CCRT CAVCA

Link: https://ivcjournal.com/hydrotherapy-canine-physical-rehab/ (with references)

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