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Hydrotherapy is the use of water to facilitate healing and movement and to enable patients to achieve therapy goals. The properties of water provide an environment for treatment options that might otherwise be difficult or impossible to provide with land-based interventions. For example, in a pool, a patient can be placed in nonweight-bearing positions—supine, prone, or sitting—with the use of buoyant devices. Movement and exercise of the upper and lower extremities can be facilitated in these positions by the effects of buoyancy. The aquatic environment created by water can serve as resistance to exercise to facilitate muscle strengthening.

Historically, hydrotherapy was delivered in metal tubs of water agitated by an attached electric motor (commonly known as whirlpools) or by immersion in larger pools of water (e.g., swimming pools). Today the use of whirlpools, particularly for treating wounds, has decreased because of infection concerns and the resources and expense required for their use. Newer techniques that deliver a pressurized stream of water to wounds and incorporate suction, such as pulsed lavage with suction (PLWS) devices, have mostly replaced whirlpools for wound care. Pool therapy, or aquatic therapy, has become increasingly popular in rehabilitation programs. Other methods of hydrotherapy, such as contrast baths, have limited support in the research literature for effectiveness.


An understanding of water’s static and dynamic properties as they apply to immersion and exercise is important to appropriately and effectively use hydrotherapy for therapeutic interventions. This section will discuss the physical properties of water, including buoyancy, drag forces viscosity, hydrostatic pressure, hydrodynamics, thermodynamics, physiological effects, and mechanics.


One of the most important properties of water is buoyancy. Archimedes’ principle states that “the buoyant force on a body immersed in a fluid is equal to the weight of the fluid displaced by that object.”1 A body or body part immersed in water will experience this buoyant force, which reduces the force of gravity on the body and, thus, decreases weight-bearing on the lower part of the body. A person immersed in water up to the neck will have about 10% of the body weight-bearing on the lower body; immersion up to the xiphoid process will bear about 33% body weight on the lower body; and immersion up to the anterior superior iliac spines will bear about 50% body weight on the lower extremities.2 Exercise of the extremities can be assisted by buoyancy. A person standing in water up to the neck can raise an extremity with the assistance of buoyancy. Buoyancy can also resist movement, such as an extremity moving downward against the force of buoyancy (Fig. 5-1). Resistance exercises for strengthening can be performed against the force of buoyancy. For example, a patient rehabilitating from surgical repair of the rotator cuff muscles of the shoulder can use the buoyant force of water ...

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