Equine Underwater Treadmills, Swimming Pools, and Spas
Therapeutic Properties of Water
Buoyancy is a lifting force exerted by a fluid that counteracts gravity (i.e. floating). This reduces weight-bearing stress (load) inversely proportional to the water depth. In horses, water at hip level results in a 75% reduction in weight bearing, whereas a 10% – 15% reduction is reported when water is at elbow height.
Viscosity is a measure of a fluid’s resistance to flow. The viscosity of water is twelve times that of air, so moving through water requires greater effort than moving through air. This increased effort causes increased muscle activity which improves muscle strength, motor control, and joint stability.
Hydrostatic pressure is the constant force exerted by a fluid over all surfaces of an immersed object. With hydrotherapy, this pressure can promote blood flow and lymphatic drainage, resulting in decreases in swelling and edema, thereby decreasing pain and improving joint mobility.
The temperature of water can produce different therapeutic effects. Cold water (cryotherapy) is used to decrease inflammation, swelling, and pain, especially at the site of soft tissue injury. Warm water immersion causes dilation of blood vessels, which may reduce local pain and inflammation.
Osmolality refers to the number of particles of solute per kilogram of solvent. Water that is higher in solute concentrations has been associated with reduced pain and inflammation. Equine studies have reported improved clinical signs in horses with tendonitis and desmitis after hypertonic cold water therapy (Hunt et al., 2001).
Hydrotherapy, the use of water to treat medical conditions, was first practiced by ancient Egyptians, and pools, saunas, baths, and tanks have historically been used to treat health concerns from arthritis to ulcers. Muscles have to work harder to move in water than on land, while the buoyancy of water reduces weight-bearing on bones, joints, and soft tissues and the pressure exerted by water reduces swelling and inflammation.
Equine hydrotherapy has become popular, with increasing investments in equipment and facilities. There are pros and cons to various approaches, but hydrotherapy generally allows for patient-specific approaches to rehabilitation and training. Swimming pools, underwater treadmills and spas have potential benefits, but more scientific studies are needed to document outcomes and inform guidelines and regulations.
Swimming pools have been the most common hydrotherapy system for equine training and rehabilitation. Pools are circular or linear, with a water depth of at least 12 feet to ensure complete buoyancy. Swim programs are associated with improvements in cardiovascular function, reductions in musculoskeletal injuries, and improved aerobic capacity. Swimming is ideal for maintaining fitness without loading limbs.
Although some horses enjoy swimming, horses are not natural swimmers. They tend to use their front legs for balance and propel themselves through the water with their hind legs. This can result in extreme ranges of motion for joints in the hind end (hip, stifle, hock). Many horses also adopt an inverted posture, especially when entering the water, which should be taken into account for horses with neck, back, or hip injuries. It is difficult to modify speed and intensity in swimming pools, as the pace is usually self-determined by the horse.
Underwater treadmill exercise is associated with improved muscle and core strength, and increased joint range of motion. Varying water depths promote increased range of motion for specific joints, with forelimb range of motion lowest, and hindlimb range of motion highest, when the water level is at the stifle. Impact shock is also reduced with increased water depth, with a roughly 30% reduction reported when the water is at stifle level.
Underwater treadmills include below and above ground units. In-ground units can hold a larger amount of water, thus creating more buoyancy. Above-ground units are able to alter the depth of the water between patients to support targeted protocols. Both types may be equipped with hydrojets to add current and increase resistance. Most units also have the ability to alter the speed of the treadmill, as well as the temperature and solute concentration of the water.
Cold saltwater spas use cold running water with a high salt content to reduce lower leg inflammation and treat minor injuries such as bruises and strains. Similar to underwater treadmills, the water level can be adjusted to alter pressure on various tissues. A study of 27 cases of tendonitis, suspensory desmitis, or lower limb injury reported fast recovery times and successful return to competition in the majority of horses after hypertonic cold spa bath hydrotherapy (Hunt et al., 2001). Saltwater spas are also used to aid recovery after exercise.
Hydrotherapy protocols should be tailored to each individual patient, taking into consideration injuries and conditions, body condition and fitness level, and goals for future athletic performance. Small adjustments in speed or water depth can have large effects. If a horse is not moving properly, decrease the water depth, speed, and/or session duration.
It is important to prioritize safety for horses and handlers during hydrotherapy. Pay attention to the horse and adjust the session accordingly. Aquatic therapy with a fearful or fractious animal should be avoided. Work with an equine rehabilitation specialist to ensure the safest and most successful outcomes.