The Properties of Water and Their Effect on Aquatic Therapy

Leslie Erin Korel Physical Therapy Program, University of Delaware

he use of water as a treatment T form dates back to ancient times with the Greeks and Romans. Even Hippocrates advocated hydro- therapy. Today water is used by therapists in the form of a tradi- tional whirlpool treatment or as an exercise medium. Almost any ex- ercise can be adapted to water by taking into account the force prin- ciples that apply to water: density, buoyancy, moment of force, hy- drostatic pressure, viscosity, and cohesion.

Current hydrotherapy began in the form of submersion of the injured extremity in either cold or warm baths. Then agitation was added in the form of whirlpool treatments. Because of the thera- peutic benefits of hydrotherapy, the practice has grown rapidly in the last 2 decades and is mani- fested as aquatic exercise therapy.

Early aquatic therapy pro- grams were based on the tradi- tional swimming strokes. But physical therapists soon realized that the properties of water al- low people to do things in water that they cannot do on land. So traditional exercise themes were adapted to the pool environment.

Now water exercise is em- ployed by therapists to treat a

-- - broad-range-of-pathologies. _ Fol:_ lowing injury, elite athletes bene- fit greatly from exercise in water because it allows them to main- tain their conditioning by mini-

mizing muscle atrophy (Levin, 1991). At the other end of the spectrum, persons who are ex- tremely arthritic or debilitated can take advantage of the buoy- ancy and warmth of water to di- minish the degenerative effects of disease or injury, maintain range of motion, and improve flexibility and overall condition (Levin, 1991).

Physiological Adaptations

The effects of exercise and the warmth of water, ideally 80 to 92 O F , work together to produce a range of physiological effects. The benefits (see Table 1) vary de- pending on intensity and duration of exercise (Haralson, 1985).

Psychological changes may be the result of the physical effects listed in Table 1, or perhaps the feeling of hope that comes from being able to do things one could not do before, even if only in the water (Routi et al., 1994).

Pertinent Properties of Water

There are six properties of water that must be understood in order to develop a water program that will yield the specific effects a therapist is looking for (Collender, 1995) :

1. Relative density 2. Buoyancy 3. Hydrostatic pressure 4. Viscosity 5. Cohesion 6. Moment of force

I Table 1 I Effects and Benefits of Hydrotherapy

Effects Benefits

- Increased circulation to the muscles

- Increased heart rate - Increased respiratory rate - Increased general muscle metabolism

_-_ - ~ecreased~,blooQpressure- ,. --- .- - Decreased sensitivity of

sensory nerve endings - General muscle relaxation

- Decreased pain - Decreased joint effusion - Improved range of motion & flexibility

- Increased strength & coordination

-+- Improved ease of ambulation & activities of daily living

- Improved mood - Increased feeling of well-being

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- portant property to understand, for it has the ability to either assist or resist motion in the water. Archimede7s principle states that when a body is partially or fully submerged in water, it experiences an upward push equal to the weight of the fluid it displaced within an area. This force is the opposite of gravity and contributes to the weightlessness a person ex- periences in water.

When a patient is submerged to chin level, it is estimated that only 1 / 10 of his or her body weight is actually supported by the joints; the rest is supported by the water's buoyancy. Harrison et al. (1992), with the help of a loading platform designed from a Salter bathroom scale, measured the actual force of patients walking in the water.

The effect of buoyancy is aug- mented by the moment of force or, more specifically, the turning effect of buoyancy on ajoint. This

I Photo 1 Hydrotherapy equlprnent that promote5 buoydncy i s an effectwe Iorm of I I water resistance exercise. I

effect increases as the limb moves toward the surface and increases the lever arm length. In practical terms, this means the ability of the buoyancy to assist movement to- ward the surface of the water is affected by the position of the limb in the water (Collender, 1995). The more horizontal the limb, the greater the buoyancy. Adding floats can also increase buoyancy.

Hydrostatic Pressure

Hydrostatic pressure is horizontal pressure that is exerted on the entire body when it is immersed in water. The amount of pressure is proportional to the depth of submersion, that is, how deep the affected area is below the surface. This has the effect of decreasing the amount of blood pooling in

the extremities (McCulloch & Boyd, 1992) and is also thought to provide some static support for unstable joints (Speer et al., 1993).

Viscosity and Cohesion

Viscosity is the amount of friction acting on a moving part in water. Cohesion is the tendency of water molecules to stick to each other. When motion occurs slowly in wa- ter, there is very little friction and little resistance from cohesion. The faster the motion, however, the greater the forces of f~iction and cohesion. It is this principle that make water exercise isokinetic in nature (Haralson, 1985).

Moment of Force

The moment of force on a body in water is defined by multiplying

March 1996 Athletic Therapy Today 37

the distance between the center of buoyancy (COB) and the axis of movement by the perpendicular force of buoyancy. When a limb nears a horizontal position in wa- ter, the effect of buoyancy on that limb increases.

One can also affect the amount of buoyancy acting on a limb by increasing or decreasing the dis- tance between the COB of the limb and the joint at which mo- tion occurs. It is this principle that allows us, for example, to increase the effect of buoyancy on the arm by holding a float at the surface or to decrease this effect by bend- ing the elbow (Collender, 1995).

Principles of Aquatic Exercise

With an understanding of these principles, a therapist can easily develop an appropriate and ac- commodating exercise program in water to help the patient progress through all stages of rehabilita- tion. The basic principles of strength and functional gains are the same as for a land based exer-

cise program (Haralson, 1985). In water, the exercise may either be assisted or resisted by buoyancy, which, as noted earlier, is oppo- site the vector force of gravity.

Buoyancy-assisted motions can be used to help increase range of motion or when a patient is un- able to perform the motion against resistance (Levin, 1991). These motions occur in a horizon- tal plane. On the other hand, buoyancy-resisted motions occur when the motion is less parallel to the surface of the water. Resistance can also be added to motion by in- creasing the speed of movement or by adding a float (Collender, 1995).

Athletic therapists need to be creative when choosing the posi- tions for exercising patients; the positions must accommodate not only the best resistance but also the relative instability some pa- tients will experience in the water. As noted earlier, most exercises that can be done on land can be adapted to water.

Functional activity and spe- cific sport or arnbulation activities

can generally be initiated earlier in the pool than on land, due to the decreasedjoint or weight bear- ing load (Tovin et al., 1994) .These may be progressed by gradually working in shallower water or in- creasing the speed of movement to increase resistance (Harrison et al., 1992).

Literature Review

Most of the literature on aquatic exercise focuses on the different patient populations or patholo- gies for which water exercise has been used. The effectiveness of water exercise versus land exercise has been studied. The consensus is that water exercise does help in- crease mobility and function for most patients but it should be used in conjunction with traditional land therapy.

In discussing the use of water exercise to rehabilitate shoulder injuries, Speer et al. (1993) re- ported that water helps patients who were not able to progress with land therapy. They suggested that the supportive effect of water gave patients enough confidence to move the shoulder, and that hy- drostatic pressure may provide biofeedback in the form of prop rioceptive information. Speer et al. noted that patients were more willing to move the limb and had less pain with exercise in water. Im- provement was immediate and this led to an increase in motivation.

Tovin et al. (1994) compared aquatic exercise with land exercise in patients with ACL reconstruc- tions. They reported that exercise in water is as effective as land ex- ercise in restoring the knee's range of motion and quadriceps strength. They also noted that aquatic exercise is more effective

Athletic Therapy Today March 1996

in reducing joint swelling and in- creasing lower extremity function.

Lefort and Hannah (1994) reported similar findings in pa- tients with lower back injuries. They found aquatic and land ex- ercise to be equally effective in increasing strength and fitness.

Conclusion

It has been proven that water can have significant rehabilitative ef- fects on elite athletes as well as on the elderly or severely disabled. Therapists can use water's buoyancy and resistance, and its warmth, to produce increases in range of mo- tion, strength, motivation, and function. Water therapy can be used at any stage of therapy.

By taking into account the principles of water pressure and resistance, therapists can adapt a water exercise program to meet the goals of almost any patient. However, aquatic exercise is most effective when used in conjunc- tion with traditional land therapy.

References

Collender, S. (1995, Oct.). [Lecture on hydro- therapy]. University of Delaware.

Haralson, K.M. (1985, April). Therapeutic pool programs: Water exercise. Clinical Management i n Physical Therapy.

Harrison, R.A., Hillman, M., & Bulstrode, S. (1992, March). Loading of the lower limb when walking partially immersed: Implications for clinical practice. Phys- iotherapy, pp. 1641 66.

Lefort, S.M., & Hannah, T.E. (1994, Nov.). Return to work following an aquafitness and muscle strengthening program for the low-back injured. Archives ofPhysical Medicine and Rehabilitation, pp. 75-87.

Levin, S. (1991, Oct.). Aquatic therapy (a splashing success for arthritis and injury rehabilitation). The Physician and Sports- medicine, pp. 119-124.

Martin, K. (1983, Spring). Therapeutic pool activities for young children in a com- munity facility. Physical and Occupational Therapy i n Pediatrics, pp. 59-74.

McCulloch, J., &Boyd, V.B. (1992, Oct.). The effect of whirlpool and the dependent position on lower extremityvolume. Jour- nal ofOrthopedicand SpmtsPhysical Thera- py, pp. 169-173.

Routi, R.G., Troup, J.T., & Berger, R.A. (1994, March). The effects of non-swimming water exercise on older adults. Journal of Orthopedic and Sports Physical Therapy, pp. 140-145.

Speer, K.P., Cavanaugh, J.T., Warren, R.F., Day, L., & Wickiewitcz, T.L. (1993, Nov./ Dec.) . A role for hydrotherapy in shoul- der rehabilitation. American Journal of Spurts Medicine, pp. 21-27.

Tovin, B.J., Wolf, S.L., Greenfield, B.H., Crouse, J., & Woodiin, B.A. (1994,Aug.). Comparison of the effects of exercise in water and on land on the rehabilitation of patients with intra-articular anterior cruciate ligament reconstruction. Physi- cal Therapy, pp. 7482.

Leslie Erin Korel is completing her master's in physical therapy at the Univer- sity of Delaware. She has taught swimming and water exercise classes for the last 4 years with Swim Masters, Inc. She co- developed the SideSwim Bar, an aquatic exercise teaching aid that facilitates correct biomechanics during the instruc- tion of rhythmic breathing.

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March 1996 Athletic Therapy Today 39