WHAT IS HYDROTHERAPY?
The word ‘hydrotherapy’ is derived from the Greek word for water healing.
To understand the benefits of hydrotherapy it helps to understand the basic properties
and principles of water. When planning a rehabilitation programme it is important
to consider these elements;
Relative Density - this is the ratio of the weight of an object to the weight of
an equal volume of water. Relative density depends on an objects composition. Specific
gravity is a pure number value measuring the density of different substances. (Pure
water = 1, fat = 0.8, lean muscle =1, bone 1.5 to 2). Relative density and specific
gravity determine how well objects float (or not!). Simply speaking, if the ratio
of the specific gravity of an object to that of water is greater than 1, then the
object will sink and if it is less than 1, the object will float. Specific gravity
of objects also determine how much of an object will float under water. Specific
gravity of ice is 0.92, therefore 92% of ice will submerge to displace enough water
(Upward force of buoyancy = downward force of gravity) 8% of ice will float above
the surface. The specific gravity of a lean animal can be as high as 1.1 and an
obese animal as low as .93. Specific gravity of an animal will mean it floats just
below the surface. The higher the specific gravity the quicker the animal will sink
i.e. a lean animal not moving will sink faster than an obese animal.
Buoyancy - is the upward thrust of water acting on a body creating an apparent decrease
in the bodies’ weight while immersed. When a body is fully or partially immersed
in water it experiences upward thrust equal to the weight of water displaced. Buoyancy
acts directly through the centre of buoyancy. Problems occur when the centre of
gravity and centre of buoyancy are not in the same vertical line causing an animal
to tilt. The use of buoyancy aids in the rehabilitation of weak muscles and painful
joints helps animals to exercise in an upright position and decreases pain by minimising
weight bearing on joints. In dogs, water at a level of the ateral malleolus of the
tibia creates approx. 91% weight bearing compared to the body weight on dry land,
at the lateral condyle of the femur - 85%, the greater trichinae of the femur -
38% and fully submerged - non weight bearing or ‘zero impact’.
Hydrostatic Pressure - Pascal’s law states that fluid pressure is exerted equally
on all surfaces of an immersed body at rest at a given depth. The deeper the body
is immersed the greater the pressure exerted on it. Hence hydrostatic pressure provides
constant pressure to a limb or body immersed in water providing an improved environment
for working with swollen joints or oedematous tissues. Hydrostatic pressure opposes
the tendency of blood and edema to pool in the lower portions of a body and can help
reduce swelling. Hydrostatic pressure can also decrease pain during exercise. Hydrostatic
pressure provides phasic stimuli to skin sensory receptors that cause a decrease
in nociceptor hypersensitivity. This decreases an animal’s pain perception which
can allow the animal to perform movements with less pain.
Viscosity and Resistance - viscosity is the measurement of frictional resistance
caused by cohesive or attractive forces between the molecules of a liquid. The viscosity
or resistance to fluid flow is significantly greater in water than in air making
it harder to move through water. This resistance strengthens canine muscles and
improves cardiovascular fitness. Viscosity also increases sensory awareness assists
in stabilizing unstable joints. A dog with paraparesis may be more willing to walk
in water or swim than on land because of the waters combined properties of buoyancy
and viscosity which help support the dog.
Surface tension - Cohesion is when water molecules adhere to each other, there is
greater tendency to adhere at the surface. Therefore there is slightly more resistance
at the surface of water. Surface tension is not a factor if the animal is completely
submerged but it becomes significant when a limb breaks the water surface. If a
patient is weak movements are easier just under the surface rather than at or on
the surface.
Exercising in water improves strength, muscular endurance, cardio respiratory endurance,
range of movement (ROM), agility and psychological wellbeing whilst minimising pain.
The primary resistant force on land is gravity; the primary resistant forces in water
are viscosity, friction and turbulence. These properties directly effect heart rate
and oxygen uptake. Exercise in water increases heart rate and oxygen uptake slightly
more than exercise on land. Exercises in water use a greater amount of energy than
the same exercise on land. Aerobic exercise used in rehabilitation improves cardiovascular
fitness and weight reduction. Aquatic exercise also benefits muscle strengthening
and minimises the amount of joint effusion leading to greater functional improvement.
Buoyancy in water eases the performance of exercise while providing proprioceptive
feedback. It allows for gentler exercise by decreasing the loads placed on injured
tissues compared to land based exercise. Hydrotherapy exercise can be used as a
transition to land based exercise in post injury or post surgery rehab.
Exercise in heated water increases circulation to muscles, increases joint flexibility
and range of movement, decreases joint pain, decreases stress in healing tissues
and minimises pain.
