Properties of Water
The reason why water has so many advantages over dry land has to do with its physical properties of specific gravity, buoyancy, viscosity, and hydrostatic pressure. Specific gravity is the weight of a substance compared to an equal volume of water. Water has the specific gravity of one and the human body is slightly less than one, so it has a tendency to float. The ability of the body to float eliminates the effects of gravity. Without having to worry about gravity, more exercises can be performed pain-free and within rehabilitation protocols.
The Archimedes’ Principle of Buoyancy states that an immersed object experiences an upward thrust equal to the weight of the water displaced. In other words, when a body is in the water, buoyancy acts in the opposite direction as gravity [1]. Buoyancy allows for upward movement to be assisted, downward movement to be resisted, and movement parallel to the water’s surface to be supported. These aspects are invaluable for exercise and rehab programs. For instance, an injured arm can be supported if movement is contraindicated, the range of motion can be assisted when it is lacking, and a strengthening program can be initiated. In addition, buoyancy creates weightlessness and in combination with water depth, certain percentages of weight-bearing for rehabilitation purposes can be determined. There are specific injuries that a doctor may prescribe only bearing a certain percentage of weight on the involved lower extremity. On land, this is just an educated guess. But in the water, the weight-bearing load to chest height for a person walking slowly is approximately 40%, while water to waist height increases the weight-bearing to approximately 60% [2]. Water takes the guesswork out and allows a gradual progression of weight-bearing for increased strengthening and return to normal activities.
Viscosity is the water’s ability to provide friction, and therefore, increased resistance to movement. This property allows water to provide a medium for strengthening. Water can act as accommodating resistance and match a person’s speed and effort, or as variable resistance when the exerciser changes the speed of their movement [3].
One principle of water, hydrostatic pressure, specifically allows water to function as a rehabilitation tool. Hydrostatic pressure increases as both the depth and density of the water increases. This pressure helps fluid that has traveled to the lower extremities return back up the body. In this way, hydrostatic pressure can help relieve swelling and assist in circulation [1].

Water, Water, Everywhere
Whether from arthritis or an ankle sprain, regaining a joint’s full range of motion (ROM) is a primary consideration. Many activities that are painful and difficult to perform on land can be easily performed in the water. Taking advantage of buoyancy allows a joint to progress through a ROM that might not normally be reached on land. Moving the joint decreases stiffness, increases nutrition, and with strengthening, can result in new gains. Aquatic therapy programs for gaining ROM post-operatively have become increasingly popular.
Water provides relaxation and pain reduction. This is especially important for tight, inflexible muscles and those that may be in spasm. With the weightlessness property of water, it is easier to perform flexibility exercises and stretch knotted muscles. In addition, the temperature of therapeutic pools (880 – 960) can promote increased elasticity of tissues and hence, muscle relaxation.
Early activity and weight-bearing for injuries is indicated to maintain joint mobility, strength, and normal walking patterns. Because of the minimal effects of gravity and the ability to determine accurate percentages of weight-bearing, the pool is considered an exceptional modality. People with injuries who cannot bear weight can exercise in neck level water and with flotation devices and gradually progress to shallower levels as weight-bearing can be increased. The pool is a safe environment to re-learn walking skills after injury or disease.
In addition to buoyancy and viscosity providing resistance for strengthening programs, other equipment can be added to enhance strengthening. Weighted water exercise equipment, hand paddles, and scuba fins can be used to exploit water’s properties. Equipment can be purchased, but it can also be made. How about filling up some empty milk containers with water for arm weights? You can use old sneakers for added weight on the feet. They are a lot heavier wet than dry.
Water running is an interesting way to maintain cardiovascular fitness while recuperating from an injury. Also, because of all the positive effects running in the water has, it can be used as a regular cardiovascular training program. Thirty minutes of hard deep water running used as much oxygen as thirty minutes of hard treadmill running, but the deep water running produced less of a heart rate increase [4]. This may be a benefit of the water’s hydrostatic pressure. Running in the water can be performed wearing a flotation vest, in shallow water, or in deep water.
Sport-specific programs can be a fun adjunct to traditional pool exercises [5]. Athletes can still participate in aspects of their sport while rehabilitating an injury or just taking a day off from their normal routine. Water improves balance, coordination, and awareness of the body [1]. This can lead to enhanced performance. Baseball and softball players can swing bats through the water, and tennis players can perfect their strokes with racquets. umping, shooting, and rebounding skills can be practiced with basketball players. Virtually anything done on land can be performed in a pool. Imagination is the only limitation.

Get Into The Swim of Things
Generally, water is very safe to exercise in, but some conditions are contraindicated. Of course, people who are afraid of the water or are allergic to pool chemicals should not try to perform aquatic therapy or exercise. Those with open wounds, infectious disease, fever, uncontrolled seizure disorder, untreated cardiac problems, untreated hypo- or hypertension, and incontinence should refrain from the pool. A doctor’s approval is always advisable before beginning any exercise program. Many conditions can benefit from the water like arthritis, fibromyalgia, and peripheral neuropathy. Virtually any exercise can be performed in the water. With aquatics having so many benefits from rehabilitation, to cardiovascular improvements, to increased strength, just add water and you can reach your goals swimmingly.

References
1. Fuller, C.S., Aquatic rehabilitation, in Physical Rehabilitation of the Injured Athlete, J.R. Andrews, G.L. Harrelson, and K.E. Wilk, Editors. 1998, W.B. Saunders Company: Philadelphia. p. 615-631.
2. Harrison, R.A., M. Hillman, and S. Bulstrode, Loading of the lower limb when walking partiallly immersed: implications for clinical practice. Physiotherapy, 1992. 78(3): p. 164-166.
3. Prins, J. and D. Cutner, Aquatic therapy in the rehabilitation of athletic injuries. Clin Sports Med, 1999. 18(2): p. 447-461, ix.
4. Ritchie, S.E. and W.G. Hopkins, The intensity of exercise in deep-water running. Int J Sports Med, 1991. 12(1): p. 27-29.
5. Huey, L., Swinging in the pool. Training and Conditioning, 1999. ix(5): p. 29-35.