Part of the reason why therapy in water is so advantageous is because of the density of water. Hydrostatic pressure is an important concept in aquatic therapy; it is the static force of the water pressing against a person or object. Also, this force creates the upward thrust that we experience known as buoyancy. It is important to note that buoyancy has a direct effect on therapeutic exercise. For example, as the patient performs standing hip abduction, the limb is assisted by buoyancy. During the limb’s return to neutral, increased hip adductor force is required to overcome buoyancy. Therefore, buoyancy can be assistive and resistive at the same time (Atkinson, 2005). A person’s body mass index (BMI), adipose tissue vs. muscle mass, is the primary determining factor in the degree to which a person sinks or floats. Muscle mass has a greater density than water, causing it to sink. Adipose tissue is less dense, causing it to float. Each individual’s unique level of buoyancy requires appropriate flotation devices or weights, depending upon the desired effects of treatment. Buoyancy allows the body to be unloaded. The greater the depth of submersion, the less the effect of gravity on body weight. A basic breakdown of buoyancy and the unloading of gravity on a patient goes as follows: waist deep 50%, chest deep 75%, neck deep 90% of body weight (Atkinson, 2005). The exact percentage of unloading may vary by gender and mass. Hydrostatic pressure increases the efficiency of the heart by helping in venous return. It also applies compression to joints, muscles and soft tissue, facilitating reduction of swelling and adding lymphatic drainage (Jamison, 2005).

Hydrodynamics, another important concept in aquatic therapy, is the force created when moving through water, causing resistance in front of the object. By changing the shape or surface area of an object, one can increase or decrease the hydrodynamic resistance (Brody & Geigle, 2009). By increasing the speed of movement, the resistance of the water becomes greater. In other words, the harder you push, the harder water pushes back. Water itself will not create a greater force of resistance than that which the individual is able to perform. This concept makes exercise in water a safe alternative to resistance training on land. Equipment, such as webbed gloves or water paddles, can be added to increase resistance. In some aquatic pools, the use of jets can add an increased level of resistance, or could be used for massage post exercise. It should be noted that an increase in water turbulence, even by a small amount, can significantly increase resistance depending on the activity (Atkinson, 2005). At other times the turbulence created by the therapist will create an increased balance challenge or facilitate the forward movement of the patient. This is important to remember when performing a group aquatic session.

A therapist or group leader should be cognizant that light refraction occurs when light passes from air to water, causing a perception of bending. This is caused by the reduction in the speed at which light is traveling upon entering the water. This bending may cause a visual disturbance to the patient’s balance mechanism (Atkinson, 2005).

A complete initial examination and evaluation by a physical therapist is essential for assessing each individual’s needs, which must be performed prior to entering the water. This requisite is to screen individuals who may not be candidates for aquatic therapy and to establish goals of care (Larsen et al., 2002; Geigle & Norton, 2005). It is important to note that some patients may need assistance changing into their bathing suits, or entering and exiting the water. Some may require full assistance throughout the entire treatment session with the clinician in the water assisting. Being in the water with the patient is advantageous but not always necessary, depending on the activity or performance level. Some aging adults may not have been in a bathing suit for many years and may feel uncomfortable or self-conscious. It is recommended that, prior to entering the pool for the first time, the patient understands what is going to happen during the session.

Water temperatures for the older adult that facilitate therapeutic benefits range from 93–95°F or 34–35°C (Larsen et al., 2002). Depending on the patient, the diagnosis and indications, the ideal water temperature may differ. A temperature less than 90°F (32.2°C) is often too cool for many older patients, because their speed of movement is typically slower, and they will not be generating as much additional body heat. Maintaining a thermoneutral water environment is important to allow for a therapeutic exercise environment. This is when the body neither gains nor loses temperature while in the water (33.5–34.5°C) (Larsen et al., 2002). Sustained exercise at temperatures greater than 95°F is too hot with respect to cardiovascular and thermoregulatory systems. Greater than 100°F is dangerous for persons with heart conditions and is considered unsafe for exercise.

The amount of work being performed by the patient is deceiving, on account of the buoyancy and resistance of the water. Thus, it is important to monitor the patient during exercise to determine exertion and fatigue levels. On land, it is common to use heart rate and oxygen saturation for monitoring a person’s level of fitness or stress on the body. However, in water, these are not the most accurate or good determiners of exertion. When comparing the cardiac response of deep water running (up to the neck) with shallow water running (up to the xiphoid process), heart rate is 10 beats per minute slower in the deeper water (Robertson et al., 2001). This is due to the hydrostatic pressure adding in venous return and other possible hemodynamic changes. It is suggested that one use a Perceived Exertion Scale, physical observation, as well as a Talk Test: shortness of breath while trying to talk will provide indications of the patient’s exertion level. Skin coloration changes may include paleness, redness, blotchiness and/or excessive sweating. These are warning signs of overexertion or overheating. When submerged in water, it is difficult for the body to thermoregulate due to the radiant and conduction temperature gain or loss in water. Simply communicating with the patient about their general feeling may provide clues as to how the patient is tolerating the level of exercise, temperature and overall intervention.

Dehydration is an important concern with the older adult. Hydration should be included in a comprehensive aquatic therapy program. Patients should be encouraged to drink 8 oz (240 ml) of water at least 1 hour before entering the pool. They should be reminded that drinking or eating large amounts prior to entering the water might cause cramping. Patients exercising in the water do sweat, and they may not realize it. Water should be available before, during and after each session. It is important to encourage patients to void prior to aquatic sessions. The hydrostatic pressure on the abdomen stimulates the internal organs and facilitates kidney function and lymph return, which may increase the need to void (Atkinson, 2005).

It is important to assess skin integrity prior to entering the water. An open wound is contraindicated for the aquatic setting, except when it is specifically being used as a wound care modality. A person’s skin may be sensitive to pool chemicals; thus, chlorine or bromine as well as pH levels need to be observed and maintained. Usually, smaller indoor pools use bromine as the sanitizing agent; larger or outdoor pools typically use chlorine. Chlorine is harder on the skin; it tends to dry it out more rapidly. Ideally, pool pH should be 7.4–7.6: higher or lower may cause skin irritation. Having the patient shower prior to and after aquatic sessions assists with the maintenance of chemical levels as well as protecting the patient’s skin. Aqua shoes may also be worn to protect feet and maintain skin integrity, especially in people with diabetes. Shoes aid in traction, increasing confidence and avoidance of falls secondary to slipping.

There are many considerations to remember when deciding if aquatic therapy is appropriate for a particular patient (Morris, 2005). In addition to medical screening and the above-mentioned concerns, there are contraindications (Hayes, 2012) for aquatic therapy, including: