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How the physical principles of water are used for Rehabilitation ?

14 Sep 2020


           Buoyancy is the property of a fluid to exert an upward force on a body that is wholly or partially submerged in fluid. Buoyancy allows the offloading of the joints and the reduction of compressive forces. As the depth of water immersion of the body increases, the weight bearing load on the joints of the body decreases. At 75% immersion, weight bearing of the lower extremities is reduced by 75%. This could benefit the patient with a low pain tolerance for compressive forces that may be present in the early stages after a total hip or knee arthroplasty.



Hydrostatic pressure 

           Hydrostatic pressure effects begin immediately upon immersion, causing a shift in fluid from the lower limb to the cardiothoracic compartment. This shift in fluid often results in a reduction of lower extremity edema. Of course, the specific hydrostatic effects on the cardiovascular system and edema dependent on depth and patient position.




           The therapeutic utility of water depends greatly on both its ability to retain heat and its ability to transfer heat energy. Water is an efficient conductor, transferring heat 25 times faster than air. This thermal conductive property, in combination with the high specific heat of water, makes the use of water in rehabilitation very versatile because water retains heat or cold while delivering it easily to the immersed body part.

           Typical therapeutic pools operate in the range of 33.5ºC – 35.5ºC, temperatures that permit lengthy immersion durations and exercise activities sufficient to produce therapeutic effects without Chilling or Overheating.




            Although the human body is mostly water, the body’s density is slightly less than that of water and averages a specific gravity of 0.974, with men averaging higher density than women. Lean body mass, which includes bone, muscle, connective tissue, and organs, has a typical density near 1.1, whereas fat mass, which includes both essential body fat plus fat in excess of essential needs, has a density of about 0.9. Highly fit and muscular men tend toward specific gravities greater than one, whereas an unfit or obese man might be considerably less. Consequently, the human body displaces a volume of water weighing slightly more than the body, forcing the body upward by a force equal to the volume of the water displaced, as discovered by Archimedes.




          Viscous resistance increases as more force is exerted against it, but that resistance drops to 0 almost immediately on cessation of force because there is only a small amount of inertial moment as viscosity effectively counteracts inertial momentum. Thus, when a person rehabilitating in water feels pain and stops movement, the force drops precipitously as water viscosity damps movement almost instantaneously. This allows enhanced control of strengthening activities within the envelope of patient comfort.



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