The Properties of Water and Their Effect on Aquatic

Leslie Erin Korel Program, University of Delaware

The use of water as a treatment mizing muscle atrophy (Levin, Psychological changes may be form dates back to ancient times 1991). At the other end of the the result of the physical effects with the Greeks and Romans. Even spectrum, persons who are ex- listed in Table 1, or perhaps the Hippocrates advocated hydro- tremely arthritic or debilitated feeling of hope that comes from therapy. Today water is used by can take advantage of the buoy- being able to do things one could therapists in the form of a tradi- ancy and warmth of water to di- not do before, even if only in the tional whirlpool treatment or as an minish the degenerative effects water (Routi et al., 1994). medium. Almost any ex- of disease or injury, maintain ercise can be adapted to water by range of motion, and improve Pertinent Properties taking into account the force prin- flexibility and overall condition of Water ciples that apply to water: density, (Levin, 1991). buoyancy, moment of force, hy- There are six properties of water drostatic pressure, viscosity, and Physiological that must be understood in order cohesion. Adaptations to develop a water program that will Current began yield the specific effects a therapist in the form of submersion of the The effects of exercise and the is looking for (Collender, 1995) : injured extremity in either cold or warmth of water, ideally 80 to 1. Relative density warm baths. Then agitation was 92 OF, work together to produce a 2. Buoyancy added in the form of whirlpool range of physiological effects. The 3. Hydrostatic pressure treatments. Because of the thera- benefits (see Table 1) vary de- 4. Viscosity peutic benefits of hydrotherapy, pending on intensity and duration 5. Cohesion the practice has grown rapidly in of exercise (Haralson, 1985). 6. Moment of force the last 2 decades and is mani- fested as aquatic exercise therapy. Early aquatic therapy pro- Table 1 grams were based on the tradi- I I tional . But Effects and Benefits of Hydrotherapy physical therapists soon realized Effects Benefits that the properties of water al- low people to do things in water - Increased circulation to the - Decreased that they cannot do on land. So muscles - Decreased joint effusion traditional exercise themes were - Increased heart rate - Improved range of motion & adapted to the pool environment. - Increased respiratory rate flexibility Now water exercise is em- - Increased general muscle - Increased strength & ployed by therapists to treat a metabolism coordination

_-_ - ~ecreased~,blooQpressure-,. --- .--+- Improved ease of ambulation --- broad-range-of-pathologies. _Fol:_ lowing injury, elite athletes bene- - Decreased sensitivity of & activities of daily living fit greatly from exercise in water sensory nerve endings - Improved mood because it allows them to main- - General muscle relaxation - Increased feeling of well-being tain their conditioning by mini- 0 1996 Human Kinetics 36 Athletic Therapy Today March 1996 Relative Density The relative density (i.e., specific gravity) of a substance affects its ability to float. The specific grav- ity of water is 1 .O.Anything with a specific gravity less than 1.0 will float. The specific gravity of the human body averages about 0.974; this depends of course on the pro- portion of fat to bone and lean body mass and on the amount of air in the lungs. The higher the % body fat and the more air that can be re- tained in the lungs, the easier it is to float. Most people will be able to float, or nearly float, and this principle also holds true for indi- vidual limbs (Haralson, 1985).

Buoyancy

Buoyancy is perhaps the most im- I Photo 1 Hydrotherapy equlprnent that promote5 buoydncy isan effectwe Iorm of I portant property to understand, I water resistance exercise. I for it has the ability to either assist or resist motion in the water. effect increases as the limb moves the extremities (McCulloch & Archimede7sprinciple states that toward the surface and increases Boyd, 1992) and is also thought to when a body is partially or fully the lever arm length. In practical provide some static support for submerged in water, it experiences terms, this means the ability of the unstable joints (Speer et al., 1993). an upward push equal to the buoyancy to assist movement to- weight of the fluid it displaced ward the surface of the water is Viscosity and Cohesion within an area. This force is the affected by the position of the opposite of gravity and contributes limb in the water (Collender, Viscosity is the amount of friction to the weightlessness a person ex- 1995). The more horizontal the acting on a moving part in water. periences in water. limb, the greater the buoyancy. Cohesion is the tendency of water When a patient is submerged Adding floats can also increase molecules to stick to each other. to chin level, it is estimated that buoyancy. When motion occurs slowly in wa- only 1/ 10 of his or her body weight ter, there is very little friction and is actually supported by the joints; Hydrostatic Pressure little resistance from cohesion. the rest is supported by the water's The faster the motion, however, buoyancy. Harrison et al. (1992), Hydrostatic pressure is horizontal the greater the forces of f~iction with the help of a loading platform pressure that is exerted on the and cohesion. It is this principle designed from a Salter bathroom entire body when it is immersed that make water exercise isokinetic scale, measured the actual force of in water. The amount of pressure in nature (Haralson, 1985). patients walking in the water. is proportional to the depth of The effect of buoyancy is aug- submersion, that is, how deep the Moment of Force mented by the moment of force affected area is below the surface. or, more specifically, the turning This has the effect of decreasing The moment of force on a body effect of buoyancy on ajoint. This the amount of blood pooling in in water is defined by multiplying

March 1996 Athletic Therapy Today 37