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Underwater treadmill therapy in veterinary practice: Benefits and considerations


An underwater treadmill, or hydro-treadmill, can be a valuable addition to any practice.

An underwater treadmill, or hydro-treadmill, can be a valuable addition to any practice. But it is important to understand its uses and limitations as well as proper operation and maintenance to achieve the greatest benefits.

In this article, we provide an overview of underwater treadmill therapy, including its purpose, common uses for specific conditions, basic techniques, necessary equipment, and maintenance considerations. We also include a case report as an example of how the treadmill can be used in the rehabilitation of a patient after anterior cruciate ligament surgery, one of an underwater treadmill's most common uses. Although the focus of this article is dogs, this modality is also growing in the field of equine rehabilitation.


Hydro-treadmill therapy is primarily used in veterinary patients to enable early return to function and improve muscle strength after limb, neck, or back surgery or injury and improve range of motion in compromised joints. Hydro-treadmill therapy is also becoming more frequently used in animals for athletic conditioning and weight management.

Orthopedic and neurologic patients can benefit from earlier return to function with underwater treadmill therapy. It provides a reduced weight-bearing environment that increases functional use of a limb without marked weight loading and resultant discomfort to a postsurgical joint.1 Patients healing from fractures in which immobilization is necessary often perform well when exercise is first initiated in water. The water's viscosity also provides increased proprioceptive and tactile stimulation.2

In addition, most postsurgical and neurologic patients have some degree of muscle atrophy or loss of strength. Muscle atrophy also occurs secondary to osteoarthritis and, to a smaller degree, as a result of normal aging. Walking on an underwater treadmill once a week or more can help patients with muscle atrophy improve strength and mobility because of the increased resistance to forward motion. More frequent sessions, as often as every other day, can help build strength even faster.

Many dogs that are unwilling to use a limb after injury will use the limb to help maintain balance and stability in the water because of increased comfort and because of the resistance to forward motion in the functional limbs, which slows the gait pattern. Underwater treadmill therapy is particularly useful in small dogs that have undergone femoral head ostectomy. In these patients, we want healthy pseudo-joint formation rather than excessive scar tissue leading to restricted motion. An underwater treadmill allows motion in a low-weight-bearing environment to help strengthen the muscles and tendons that surround this new joint as well as maintain strength and balance in the rest of the body. The reduced weight-bearing stress on the limb in the initial phases of pseudo-joint formation appears to help to reduce the amount of functional limb length discrepancy associated with dorsal displacement of the femur in these patients.

Injured joints often show reduced range of motion. Underwater treadmill walking allows a correct but exaggerated gait pattern, which improves joint flexion, and to a lesser degree, extension.3 The most common example of a patient that would benefit from this exaggerated gait pattern is a patient with limited stifle and hock flexion after undergoing surgery to repair an anterior cruciate ligament injury (see the related sidebar titled "A case example of physical rehabilitation in a dog after bilateral stifle surgery").

The pain relief provided by warm water facilitates muscle relaxation and tendon stretch in situations in which splinting, protection, or contracture has occurred.1

Athletes benefit from conditioning on an underwater treadmill both in muscle strengthening and cardiovascular endurance because of water's increased resistance.

Finally, obese or overweight patients can exercise more safely in a buoyant environment than on land. The water's buoyancy reduces weight-bearing stress while at the same time its resistance increases metabolic demand and improves muscle strength.1


Swimming can also be used as a mode of aquatic therapy. Its uses and benefits are similar to those of an underwater treadmill, but it has a few key differences.1,4 Swimming dogs use a different pattern than a walking gait, so it may not be ideal for gait retraining in a dog with a neurologic injury.5 Water in most tanks can be adjusted to a sufficient depth to allow even a large dog to free-swim. Some equipment allows the use of jets to provide resistance.

Some facilities use a separate pool for swim therapy, allowing more room for a natural swim environment. In some cases, swimming can be done in lakes or in the ocean, but these are less-controlled and, thus, more risky environments.


Some patients may be fearful of water, but most are willing to exercise on an underwater treadmill if they are slowly introduced to the equipment and the water. If a patient is fearful of the underwater treadmill, treats placed on the ramp and tread, or a frozen cup smeared with peanut butter, can often motivate such a patient to get into position to walk.

Patients with cardiac or respiratory disease may experience more difficulty exercising in water than on land. However, most of these patients can exercise on an underwater treadmill if properly monitored and exercised conservatively.1 Increased resistance in the water causes increased cardiovascular and respiratory demand. Short sessions of exercise followed by sessions of rest (initially walking one minute, resting two minutes, repeating twice) may be more appropriate for these patients. The patient is never exercised to the point of fatigue, and its respiratory rate is closely monitored with exercise ceasing before panting occurs.

As with any active therapy, each patient's general health must be evaluated before initiating therapy to ensure it is capable of safely and comfortably performing the activity. In addition to general health concerns, the practitioner must determine if a patient's pain level is too great to initiate active exercise. In most situations, patients in pain derive relief from aquatic activity.1 Initially, a therapist may choose to perform passive range of motion or standing exercises with the patient in the water and progress to active walking when the patient is more comfortable.

Certain instabilities (such as spinal instabilities) may need to be resolved before initiating underwater treadmill therapy. Some patients with instabilities may be safely exercised underwater.3 Many experienced practitioners will initiate underwater treadmill therapy before anterior cruciate ligament surgery and in some instances when surgical correction is not possible.

It is also best to avoid immersing a newly sutured area, a large wound, incontinent patients, or patients with diarrhea. Hot spots will heal faster because of the sanitation system in the water as long as the patient is dried thoroughly in the affected area. As a general rule, any condition that would warrant caution for land exercise would also warrant caution for water therapy.

If a dog is tetraparetic, there should be at least two or three people in the pool with it: one to work with the rear limbs, one to work with the forelimbs, and if the patient is unable to control neck motion, a third person to prevent head submersion. Several tanks are too small to accommodate this many people, so this need should be a purchasing consideration if a practice works with neurologic patients frequently.


Many treadmill parameters, such as water depth and turbulence and walking speed and direction, need to be determined each session to best achieve the desired outcome for a patient. Water temperature may also vary, but this variation occurs less frequently in practice than the other parameters.

Water depth

Changing the water depth can markedly alter a patient's motion and exercise exertion level. A low water level, just above the carpus (91% weight-bearing), increases carpal and hock flexion more than any other level does and is useful in patients with reduced flexion of these joints.6 When the water is at elbow level, there is significant resistance with minimal buoyancy (85% weight-bearing)6 since the chest is not displacing water. This level is excellent for dogs you want to increase strength and endurance in, such as athletes. Water levels at or just above the shoulder have maximum buoyancy for strengthening the limbs with minimal joint load (38% weight-bearing) and are most beneficial in patients with osteoarthritis or recovering from surgery in which full weight-bearing is contraindicated or painful.6 Water levels above this level cause dogs to shorten their strides, which can reduce the exercise's benefit.

Treadmill speed

Increasing the treadmill speed increases a patient's exertion through turbulence and resistance. Slow speeds (0.1 to 0.6 mph) are used in dogs that have neurologic problems since the viscosity of the water gives patients more reaction time and patients are more likely to step correctly instead of dragging their feet. Moderate speeds (1 to 2 mph) are used for most postsurgical and arthritic patients initially and to warm up and cool down athletes. Fast speeds (2.2 to 5 mph) are used for athletes and stronger patients that are more advanced in their rehabilitation.

Limb length and, thus, stride length are used to determine a starting speed. In our experience, a medium-sized dog just starting out on an underwater treadmill does best with initial speeds of 1 to 1.5 mph, which results in a comfortable, brisk walk.

Walking direction

Although used less frequently than forward walking, backward walking strengthens the biceps femoris, semitendinosus, semimembranosus, and superficial, middle, and deep gluteal muscles, which are often the muscles that weaken markedly in older patients, patients with metabolic or musculoskeletal disease, and patients with degenerative myelopathy. These muscles are also important for jumping, so backward walking is also an excellent exercise for athletes. The duration of backward walking is markedly shorter than that of walking forward since backward walking is more difficult. We usually start with 30 to 45 seconds and rarely go longer than five or six minutes, even with our athletic patients.

Water turbulence

Another option available with some underwater treadmill units is increased turbulence through the use of jets (Figure 1). Turbulence increases the exertion level, thus working the cardiovascular system and muscles more intensely than without the jets. At our practice, jets are used with any patient that can walk for 20 minutes on the underwater treadmill without becoming fatigued. Athletes, patients with degenerative joint disease, geriatric patients that have become weak from inactivity, and patients with hip dysplasia are a few examples of when jets can be added to the protocol. Jets should not be used with patients that have an unstable stifle or that have recently had cruciate surgery since the jets can increase the shear force applied to the tibia.

1. A patient walking on an underwater treadmill with jets for added resistance under the guidance of Sierra Nash, treatment assistant.

Water temperature

Cold water and warm water have different physiologic effects. Cold water (below 85 F [29.4 C]) tends to reduce the heart rate, which can be beneficial when exercising for conditioning. Warm water (86 to 94 F [30 to 34.4 C]) has negligible effects on cardiorespiratory parameters and exertion but increases circulation and flexibility, thereby reducing discomfort.7


The length and number of repetitions depends on the patient's athletic ability and the therapist's goal. If a patient has incurred an injury that has healed but it still refuses to apply weight to a limb, we will put the patient on the underwater treadmill with the intention of tiring the other three limbs to encourage the patient to use the fourth. This may be five to 10 minutes. This technique often eliminates the abnormal behavior within two to four sessions. On the other hand, debilitated patients may start out with three repetitions of 45 seconds with two-minute rests in between. The average patient starts off with three repetitions of one or two minutes and works up to 20 minutes. When this protocol is no longer a challenge, other variables are changed.


A therapist's training is the most crucial investment you make when starting an underwater treadmill therapy program and is best accomplished before purchasing the unit. Training better ensures an educated purchase and is a sign of your commitment to a comprehensive underwater treadmill therapy program. A skilled therapist has a repertoire of techniques that can be used to benefit a patient: Where to stand and place hands, when to use assistive devices, and which devices to use are all factors that can affect the success of a therapy session or program.

Having an experienced practitioner train a new therapist is the best way to ensure that an adequate level of expertise is attained before initiating a rehabilitation program. Two certification programs teach animal rehabilitation: Animal Rehabilitation Institute and Northeast Seminars (through The University of Tennessee). Both train licensed veterinarians, veterinary technicians, and physical therapists and are a good resource for training existing staff or hiring an experienced therapist.

Body position

The therapist's body position can affect a patient's attitude and focus. The therapist may encourage forward progress from the front, side, or rear of the patient (Figure 2). For an even gait, the patient should be facing forward at all times.

2. Note the treatment assistant's position while a patient walks backward on the treadmill.

A therapist can help a patient while it is on a treadmill in many ways. For example, holding the tail up with slight traction can aid a patient that tucks its pelvis and has a reduced posterior stride. The therapist may also assist a neurologically weak patient by standing behind it and squeezing the hamstring muscles at the end of the posterior phase of the stride to achieve stronger forward motion in the anterior phase. In a scoliotic patient with spinal concavity on the right, placing a hand on the right side of the pelvis and the left side of the rib cage can help the patient walk straighter.

Assistive devices

When water's buoyancy is inadequate to maintain a proper topline and, thus, proper biomechanics, a harness (e.g. Walkabout Harness—Walkabout Harnesses; Help 'Em Up Harness—Blue Dog Designs; harnesses and strap accessories provided by the treadmill manufacturers) can be placed on the patient. This harness is attached by a nylon strap or a bungee cord to either an eyehook in the ceiling or a bar that is supported by the tank. The harness permits increased difficulty by allowing for mild side to side and up and down motion that engages the trunk musculature. This assistance allows the therapist to work with the patient's limbs without worrying about its balance.

Most assistive devices that help patients improve walking on land can also be used underwater, but be aware that the effects may differ. For example, although weights might be used out of water to achieve increased flexion or resistance, balloons or water wings are more appropriate underwater (Figure 3).

3. The patient is wearing a balloon to increase stifle flexion and increase surface area to amplify resistance.


Several commercial treadmills are available. The best way to evaluate a treadmill is to work with a functional unit after receiving appropriate training. In addition, experienced practitioners who already use underwater treadmills may be excellent sources of information about the ease of use and maintenance of a particular unit.

Companies that produce or distribute commercially available models and some that will build a custom model include:

Appropriate gear (e.g. wetsuits, nonslip shoes) is a good investment to keep the therapist safe and warm. A blow dryer for patients is essential in cooler climates, but towels may suffice in warmer areas. Toys and harnesses for patients are also helpful.

Other considerations when purchasing an underwater treadmill include adequate space for the pool and filtration system, a water source to fill the pool, and drainage availability when the pool needs to be partially or fully drained. If a basement is not available to store the filtration system, in some areas of the country the holding tank can be placed outside the building with piping coming in to diminish the spatial requirements. Water-filled pools are also quite heavy, so flooring strength is important as well.


Each unit has unique maintenance requirements, but all require some mechanical maintenance and sanitation. Underwater treadmills can be used with salt water or fresh water and can be sanitized with chlorine (may make dogs vomit or have diarrhea if they ingest a substantial amount), bromine, or copper. Ozone can be added to aid in disinfection and lower the amount of primary sanitizer needed to maintain a safe environment. Sand filters or cartridge filters can be used, but they need to be large since a considerable amount of oil and particulate are expelled from canine coats. A local pool store has the ability to test your water for particulate as well as chemicals. If you let them know how many gallons are in your tank, they have a computer system to tell you what you need to add. It is usually a free service.


In our experience, underwater treadmill therapy can be beneficial not only in patients with injuries but also in patients with osteoarthritis and obesity. Additionally, it can be used for conditioning healthy canine athletes. This wide scope of use can make underwater treadmill therapy a great addition to many practices.

Christine Jurek, DVM

Laurie McCauley, DVM

TOPS Veterinary Rehabilitation

1440 E. Belvidere Road

Grayslake, IL 60030


1. Levine D, Rittenberry L, Millis DL. Aquatic therapy. In: Millis D, Levine D, Taylor RA, eds. Canine rehabilitation and physical therapy. St. Louis, Mo: Elsevier Saunders, 2004;264-276.

2. Ruoti RG, Morris DM, Cole AJ. Aquatic rehabilitation. Philadelphia, Pa: Lippincott Williams & Wilkins, 1997:71-79.

3. Jackson A, Millis D, Stevens M, et al. Joint kinematics during underwater treadmill activity, in Proceedings. 2nd Int Symp Rehabil Phys Ther Vet Med 2002;191.

4. Marsolais GS, McLean S, Derrick T, et al. Kinematic analysis of the hind limb during swimming and walking in healthy dogs and dogs with surgically corrected cranial cruciate ligament rupture. J Am Vet Med Assoc 2003;222(6):739-743.

5. Zink MC. Peak performance: coaching the canine athlete. 2nd ed. Lutherville, Md: Canine Sports Productions, 1997.

6. Tragauer V, Levine D, Millis DL. Percentage of normal weight bearing during partial immersion at various depths in dogs, in Proceedings. 2nd Int Symp Rehabil Phys Ther Vet Med 2002;189-190.

7. Dunning D, McCauley L, Knap K, et al . Effects of water temperature on heart and respiratory rate, rectal temperature and perceived exertional score in dogs exercising in an underwater treadmill, in Proceedings. 3rd Int Symp Rehabil Phys Ther Vet Med 2004;217.

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