Aquatic therapy carried out in a treatment pool makes use of the host of beneficial effects exerted by water on the human body.
A body immersed in water appears to lose an amount of weight equal to the weight of the liquid it displaces (principle of buoyancy). As a result, weight is taken off the joints and the muscles are freed from the constant work of counteracting gravity. Owing to its viscosity, water puts up great resistance to fast movements; in contrast, slow movement are easier in water. This resistivity of the water can be used to strengthen the muscles.
The warmth of the water in the treatment pool activates the sensitivity of the skin to touch and pressure and stimulates movement activity.
As a result of the hydrostatic pressure encountered when the human body is immersed in water, blood pooled in the legs and pelvic region is mobilized and places a load on the heart. For this reason, the treatment pool is "off limits" for patients with decompensated cardiac insufficiency or pulmonary insufficiency.