Aquatic Therapy

Historical documentation of the use of water as healing medium can be traced as for back as 2400 B C. Not until the later part of 1890 did aquatic therapy moved from passive immersion in to treatment technique that involved patient participation.

Physical properties of water

The effects of physical properties of water should be considered when planning for aqua therapy

 Relative density (specific gravity)

  It is the ratio of the density of a given substance to the density of water. Pure water has a specific gravity of 1. If a person´ s body or extremity has a specific gravity < 1, it has a tendency to float, where as if a person has a specific gravity > 1, it has a tendency to sink. The specific gravity of the client needs to taken into consideration when placing him in an aquatic medium. The clinician must determine whether the client is sinker or floater. It is also needed to put into consideration use of floating device


The Archimedes principle states that when a body is fully or partially immersed in a fluid at rest, the body experiences an upward thrust equal to the weight of the displaced fluid.

Buoyancy is defined as the upward thrust acting in the opposite direction of gravity and is related to the specific gravity of the immersed object

Buoyancy can be considered as a force that can assist, resist or support movement

Buoyancy can assist movement if the extremity is moving from a vertical position in the water to horizontal position, parallel with the water’s surface. Buoyancy assist movement can be used for isometric muscle contraction at various angles through an arc of movement of a joint or limb

Buoyancy resist is defined as the movement of an extremity from a starting a horizontal position (parallel to water’s surface) deeper into the water (to a vertical position)  

Buoyancy support movements are performed when an extremity is lying on the water’s surface (or just below it) and is moved parallel to the surface. Buoyancy support movement can be equated to the gravity eliminated movement performed on land

Buoyancy also plays a significant role in the progression of weight bearing status in the water, thus allowing rehabilitation to start much sooner. Such conditions include .degenerative disk disease, partial discectomies, spinal fusion, compression fractures of the spine from trauma or osteoporosis, degenerative joint disease of the spine or extremities such as osteoarthritis, and joint replacement.

Hydrostatic pressure ( Pascal´s law)

Pascal´s law states that, at any given depth, the pressure from a liquid is exerted equally on all surfaces of the immersed object. Hydrostatic pressure is also directly proportional to the depth of immersion of the object below surface level

Peripheral edema in the foot and ankle can be decreased through the use pf hydrostatic pressure  

Because hydrostatic pressure exerts an equal force at a given level of water depth, the water provides a safe supportive environment in which to start early balance and proprioceptive   training. Compression on all submerged surfaces of the body by the hydrostatic pressure of water also activates peripheral sensory nerve endings for early proprioceptos input to the trunk and extremities

Viscosity, Cohesion, Adhesion and Surface Tension

-Viscosity refers to the magnitude of internal friction among individual molecules in a liquid .it affects an individual or an object moving in a fluid, acting as a form of resistance when the water molecules stick to the surface of the object attempting to move through the water .Likewise, viscosity is time dependant property of a liquid and is described as distance over time .The faster an object moves through a liquid , the greater the viscosity and, therefore the greater the resistance to movement


-Cohesion is the force of attraction among molecules within the same substance, such as the attraction of one water molecule to an other water molecule

-Adhesion is the force of attraction among molecules of two different types of matter such as air and water at the air-water interface or water and glass molecule at the water glass container

Surface tension is a force created by the cohesive and adhesive properties of the water molecules at the air water interface. It acts as a resistance for movement in the water ( e.g when an extremity moves from the water to the air and vice versa


It causes the bending of light rays as they pass from amore dense to a less dense medium and vice versa .consideration of this property is important when the clinician is viewing the position of a body or extremity from above the water level  

Fluid Dynamic properties of Water

  Streamlined versus turbulent flow  

Streamlined or, laminar flow of water is defined as a steady, continuous flow of water molecules in one direction in which the molecules are traveling parallel to each other

Once the flow of water reaches a critical velocity level, the water molecules begin to move in an irregular fashion, causing rotary movement of molecules (known as eddies) and creating turbulent water flow .the resistance to movement in turbulent flow is proportional to the square of the velocity


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