 Byline: Andrea Salzman, MS, PT
Improvement in balance is caused by the ability to make movement errors and correct for them and the water provides an environment in which this can be attempted safely. Hypothesized benefits are improved balance and improved sensory awareness.
Hypothesis: Patients may be challenged beyond limits of stability in the water without the fear of consequences of falling which are often present with land-based balance training. The environment leads to improvement in balance reactions which are translatable to land.
Building an Argument
I. Hydrodynamic principles
Movement through water is affected by turbulence and viscosity. Water is more viscous than air, and resistance to flow through water is greater than resistance to flow through air. Thus, it takes more force to push through water molecules than to push through air molecules. Additionally, the faster an object is pushed through the water, the more turbulence is created and this creates additional resistance to movement.
Richley Geigle et al argue that somatosensory input is increased more by moving an object through a viscous liquid than by moving through a less viscous gas (air). They postulate that resistance to movement may "cause distention or stretch of the skin resulting in stimulation of rapidly adapting mechanoreceptors, perhaps contributing to better proprioception." [1] A body immersed is surrounded by a viscous fluid which retards the speed of movement. This viscosity prevents rapid falling and elongates the period of time in which a patient can respond to a shift of his center of mass outside his base of support. Additionally, the natural end result of a loss of balance which is not corrected is a fall into a compliant fluid (water) and not a fall to a noncompliant solid (the ground).
Thus, the patient may be challenged to move outside his base of support without fear of traumatic consequences. This reduction in patient anxiety may encourage the patient to attempt tasks which he would not attempt on land. It becomes possible to elicit balance challenges which the patient has both time and mental confidence to combat. On land, without the assistance of such aquatic properties, the resultant balance responses may be incomplete or absent. Water offers a three dimensional environment of both support and resistance. Any object with a specific gravity of less than one will tend to float toward the surface of the water. Alternatively, any object with a specific gravity less than one will sink.
According to Richley Geigle et al, these forces combine to "create multiple combinations of joint angles and planes of motion which are assisted, supported or resisted to various degrees. The therapist may use these combinations in the water to challenge the patient beyond his or her limit of stability, without the fear of the consequences of falling which are often present with land-based balance training." [1]
II. Clinical Research
Simmons and Hansen tested the effects of exercise, immersion in water, socialization and a combination of all these factors on balance control. [2] Subjects were divided into four groups: water sitters, land sitters, water exercisers and land exercisers. These four groups were created to attempt to isolate the factors which improve gait: exercise alone (land exercise), water immersion (water sitting), socialization (land sitting) or exercise in a medium which permitted multiple "movement errors" without fear of falling
(water exercise). All groups met for 45 minutes, 2x/week for five weeks with the supervision/instruction of a physical therapist.
Exercise in the water enhanced the functional reach (FR) of the subjects more than did socialization, water immersion or exercise alone. FR improved over 35 cm by week five and resulted in continued participation in exercise, no orthopedic injuries and some subjects discarding their assistive gait devices.
Conclusion
In addition to the above, Simmons and Hansen found that the water exercisers adhered to their program, as evidenced by better attendance rates. The authors postulate that the improvement shown by the water exercisers was due to their ability to make and correct for movement errors in a viscous, safe environment which provided proprioceptive feedback to movement. The authors felt that land-based exercise may be too intimidating for those with balance deficits; the cost of loss of balance is much greater than it is in water. The water's turbulence, inherent destabilizing effect, and depth-dependent buoyancy effect may enhance the variability of practical effect needed to learn compensation for loss of balance.
References
1. Geigle, P.R., Cheek, W.L., Gould, M.L., Hunt, H.C., & Shafiq, B. (1997). Aquatic physical therapy for balance: The interaction of somatosensory and hydrodynamic principles. Journal of Aquatic Physical Therapy, 5(1), 4-10.
2. Simmons, V., & Hansen, P.D. (1996). Effectiveness of water exercise on postural mobility in the well elderly: An experimental study on balance enhancement. Journal of Gerontology, 51A(5), M233-M238.