FLUID MECHANICS AND HYDROTHERAPY

FLUID MECHANICS
Hydrotherapy / Aquatic exercise/ Aquatic therapy/
Aquatic Physiotherapy

Introduction
● The use of water for healing purposes dates back several centuries.
● Near the end of the 19th century in Europe, and soon after in the United States, the
use of an aquatic environment to facilitate exercise began to grow in popularity.
● In recent years, healthcare practitioners have increasingly utilized the aquatic
medium to facilitate therapeutic exercises.
● The unique properties of the aquatic environment provide clinicians with treatment
options that would otherwise be difficult or impossible to implement on land.
● Through the use of buoyant devices and varied depths of immersion the practitioner
may position the patient supine, seated, kneeling, prone, side-lying or vertically with
any desired amount of weight bearing .
● Aquatic exercise has been successfully used for a wide variety of rehabilitation
populations including paediatric,orthopaedic,neurological, and cardiopulmonary
patients.

● Physiotherapists can help people maintain movement and function of joints
and muscles with exercises, hydrotherapy (exercise in warm water),
relaxation techniques and various other treatments.

Definition
● Aquatic exercise refers to the use of multi depth immersion pools or tanks that
facilitate the application of various established therapeutic interventions, including
stretching,strengthening, joint mobilization, balance and gait training, and endurance
training.
● “ The term encompasses a broad range of approaches and therapeutic methods
that take advantage of the physical properties of water, such as temperature and
pressure, for therapeutic purposes, to stimulate blood circulation and treat the
symptoms of certain diseases .”
● Application of water, internally or externally, for the treatment of physical or
psychological dysfunction.
● Hydrotherapy involves exercising in water

● Hydrotherapy is used in the treatment of a wide range of conditions to
enhance cardiovascular fitness, to mobilise, to strengthen, to coordinate
movement and to regain function of the neuro-musculoskeletal system.
● Many hospital departments have purpose-built heated hydrotherapy
pools.
● The warm environment may allow the muscles to work more effectively
owing to a rise in temperature and of the relaxation of any muscle spasm.
It will also have a pain-relieving effect.
● Conditions commonly managed by hydrotherapy are wide ranging, from
rheumatological conditions such as rheumatoid arthritis and ankylosing
spondylitis to trauma cases and neurological conditions.

● Hydrotherapy , is a specific form of physiotherapy treatment conducted in a
heated pool.
● This treatment (individually or in groups) incorporates individual assessment,
diagnosis and the use of clinical reasoning skills to formulate a treatment
program appropriate to each patient’s needs.
● A series of general therapeutic exercises (distinct from swimming or
aqua-aerobics) carried out in a heated pool allow greater comfort and range
of movement as the water supports body weight.
● Therapeutic exercises can be progressed safely using the resistance of the
water to strengthen the muscles and improve stability.

● The starting positions used to exercise in the pool will be different from those commonly used on dry
land.
● Patients commonly exercise in standing or sitting in the pool or perform more dynamic exercises
such as walking or swimming, but they can also be treated while floated in lying.
● Floats are placed around the neck and waist to support the patient, allowing the patient to exercise
freely.
● Floats may also be placed around the limbs.
● The factors that need to be considered, other than starting position, that change the nature of the
exercise are those of
○ Buoyancy,
○ Turbulence and
○ streamlining.

● A fluid is a substance which will deform continuously under the action of shear
stress & may be either a gas or a liquid.
● A gas completely fills the space in which it is contained and is easily
compressed.
● A liquid usually has a free space & is compressed with difficulty.

● Fluid mechanics is the study of fluid behavior (liquids, gases, blood, and
plasmas) at rest and in motion
○ Hydrostatics
○ Hydrodynamics

Hydrostatics
● Fluid statics or hydrostatics is the branch of fluid mechanics that studies “fluids at rest and the pressure in a fluid
or exerted by a fluid on an immersed body”.
● It is the study of force & pressure in a fluid at rest.
● Hydrostatic is basically concerned with fluids at rest .

Hydrodynamics
● Hydrodynamics deals with fluids which are in motion.

Pascal law
● When a fluid is at rest, the pressure on the liquid is the same at all points provided, they are of the same height.
● Pascal՚s law is a principle in fluid mechanics given by Blaise Pascal that states that a pressure change at any point
in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs
everywhere.
● The change in pressure which has been applied on the fluid which is enclosed can be transmitted undiminished to
every point of the fluid and the container vessel՚s walls.
● When an incompressible fluid is passing between every second in a pipe of non-uniform cross-section, the volume
will be the same as the steady flow.

Bernoulli՚s principle
● Bernoulli՚s principle is an equation which states the conservation of energy of non-viscous fluid motion in a steady
state.
P=F/A
Where,
● P = Pressure
● F = force
● A = area

Properties of Water
● The unique properties of water and immersion have profound physiological
implications in the delivery of therapeutic exercise.
● To utilize aquatics efficiently, practitioners must have a basic understanding
of the clinical significance of the static and dynamic properties of water as
they affect human immersion and exercise.
● The properties provided by buoyancy, hydrostatic pressure, viscosity and
surface tension have a direct effect on the body in the aquatic environment.

PHYSICAL
PROPERTIES
OF WATER
VISCOSITY
BUOYANCY
HYDROSTATIC
PRESSURE SURFACE
TENSION

Operational Properties behaviour of Fluid
❏ Viscosity
❏ Viscosity index
❏ Pour Point
❏ Neutralisation Number

Fundamental fluid Properties
1) Density
2) Specific Weight
3) Specific Volume
4) Specific Gravity
5) Surface Tension
6) Capillarity

PROPERTIES OF WATER
Water has the properties common to all liquids.
1. Water is a compound consisting of hydrogen and oxygen.
2. At Normal temperature and pressure it is a colourless , tasteless,
odourless liquid.
3. It solidifies at 0°C(32° F) and vaporizes at 100°C( 212°F)
- The temperature of the human body is normally 36-37°C.
- The temperature of a hot bath is approximately 41°C, that of a hydrotherapy
pool somewhere between 33°C and 38°C (91° F-100.5° F)

4. It takes the shape of its container, making perfect contact with the walls of the
container and with any object immersed in it. This is one of the factors which
makes water a suitable coupling medium for ultrasound treatments.
5. It retains its volume, being practically incompressible. So, resistance is offered
to any movement which tends to compress the water. With some movements this
resistance is small and most noticeable if muscles are weak , but the resistance is
appreciable if the palm of the hand is slapped down on the surface of the water, or
in the case of a ‘flat’ dive.

6.Cohesion
● Runs parallel to the direction of the water surface
○ Result of water molecule surface tension
● There is cohesion between the molecules of water, i.e., they are attracted to each other rather than to molecules of other
materials.
● The amount of cohesion varies in different materials and is not very marked in water.
● Cohesion tends to cause a liquid to take the shape which gives the smallest possible surface area for the volume,i.e., a
sphere.
● In spherical droplets of water the maximum number of molecules are in contact with those of their own kind, the minimum
number in contact with those of other materials.
● Cohesion is thus responsible for surface tension, which makes a liquid behave as if it were covered by an elastic skin, as
the molecules tend to retain contact with others of their own material.
● Neither of these effects is very marked with water but surface tension does offer slight resistance on entering or leaving the
water and on performing movements with the body partially immersed.
● Cohesion is also responsible for the viscosity or ‘stickiness’ of a liquid.
● Because the molecules tend to stick together there is friction between the molecular layers of the liquid which prevents it
from flowing freely.
● As cohesion between the molecules is slight water shows little viscosity.

7.Adhesion
● Adhesion is more marked with water than is cohesion.
● It is a tendency of the molecules to stick to those of other materials.
● If the hand is dipped in water, water molecules adhere to it.
● This does not occur with mercury, which has more cohesion but less adhesion than
water.
● Adhesion causes a slight resistance to movement.
● A layer of water adheres to an object immersed in it and the friction between this
and other layers of water (viscosity) must be overcome for movement to occur.
● The resistance is less than the frictional resistance encountered on a dry surface,
but more than that in air.

8.Diffusion
● Water molecules are in a state of continual movement so diffusion occurs
fairly readily, this being a mixing of substances in contact with each other or
separated by a permeable membrane.
● A substance introduced into one part of an exercise pool therefore tends to
diffuse throughout.

9.Viscosity
● Viscosity is friction occurring between molecules of liquid resulting in resistance to flow.
● Viscosity of a fluid is the measure of its resistance to gradual deformation by shear stress or tensile stress.
● It is the thickness of fluid ( have high viscosity whereas water has less viscosity)
● At a molecular level , viscosity is a result of the interaction between different molecules in a fluid. This can be also
understood as friction between the molecules in the fluid)
● Resistance from viscosity is proportional to the velocity of movement through liquid.
● Water’s viscosity creates resistance with all active(AROMs) movements.
● A shorter lever arm results in increased resistance . During manual resistance exercises stabilizing an extremity
proximally require the patient to perform more work . Stabilizing an extremity distally requires the patient to perform
less work .
● Increasing the surface area moving through water will increases resistance .

10.Viscosity Index(VI)
● It is an arbitrary , unitless measure of a fluid’s viscosity change relative to a temperature change, mostly used to
characterise the viscosity- temperature behaviour of lubricating oils.
● The higher the VI, the smaller the change in fluid viscosity for a given change in temperature and vice versa.
● The lower the VI , more the viscosity is affected by temperature changes.
Where ,
L= viscosity of low viscosity index oil at 100℉;kinematic viscosity of an oil at 40 °C of 0 viscosity index having the same kinematic viscosity at 100 °C
as the oil whose viscosity index needs to be calculated, mm2 /s,
U= viscosity of sample oil at 100℉;kinematic viscosity at 40 °C of the lubricant or petroleum product whose viscosity index needs to be
calculated, mm2 /s.
H= viscosity of high viscosity index oil at 100℉;kinematic viscosity of an oil at 40 °C of 100 viscosity index having the same kinematic viscosity at 100
°C as the oil whose viscosity index needs to be calculated, mm2 /s.

Properties that influence viscosity include
❖ cohesion (the attraction of water molecules to adjacent water molecules),
❖ adhesion (the attraction of water molecules to the person’s body), and
❖ surface tension (the attraction of water molecules on the surface to each other).

11.Pour Point
● The Pour point of a liquid is the temperature below which the liquid loses its flow characteristics.
● In crude oil, a high pour point is generally associated with a high paraffin content.
● Typically found in crude

12.Neutralisation number
● Lubricating oils acidity or alkalinity is determined in terms of neutralization
number

13.Surface Tension
● The surface of a fluid acts as a membrane under tension.
● Surface tension of a liquid is defined as force per unit length.
● Acting on surface perpendicular to one side of imagined line to drawn on the surface.
● Surface tension is measured as force per unit length.
● The attraction of surface molecules is parallel to the surface.
● The attractive forces exerted upon the surface molecules of a liquid by the molecules beneath tends to draw the
surface molecules into the bulk of liquid & makes the liquid assure the shape having the least surface area.
● The attractive forces due to air interface with liquid. If liquid interface with other liquid known as Interface Tension.
● The resistive force of surface tension changes proportionally to the size of the object moving through the fluid
surface .
● An extremity that moves through the surface performs more work than if kept under water .
● Using equipment at the surface of the water will increases the resistance.

● It is referred to the force per unit length which is acting on the plane of the
interface between the bonding surface and the liquid.
● Surface tension is the tendency of liquid surfaces to shrink into the minimum
surface area possible.
● It is the amount of the extra energy which the molecules at the interface
have when compared to the interior.
● Surface tension allows insects, to float and slide on a water surface without
becoming even partly submerged.

14.Hydrostatic Pressure
● Hydrostatic pressure is exerted in all directions as the moving molecules collide with each other, the walls of the
container and any object immersed in the water .
Hydrostatic Pressure is the pressure exerted by fluid on an immersed objects.
Pascal Law states that the pressure exerted by fluid on an immersed object is equal on all surfaces of the
object.
Or in other words
“ water exerts an equal force in every direction. ”

● Thus at any point within it the water is exerting the same constant force from
below , above and on all sides .
At any point in a fluid, equal pressure is exerted (and experienced) in all directions

● As the density of water and depth of immersion increase, so does hydrostatic
pressure.
● The proportionality of depth and pressure allows patients to perform exercise
more easily when closer to the surface.
● However , the pressure does increase with depth and is greater in more
dense fluids.
● Increased pressure reduces or limits effusion , assists venous return , induces
bradycardia , and centralizes peripheral blood flow.

● When the human body is immersed in water the pressure provides support in
the vertical position and also , if the abdominal muscles are weak, a ‘corset’
effect which aids vasomotor control.
● Drainage from an oedematous limb is aided , and because the pressure
increases with depth such a limb is best treated well below the surface.
● Respiration may be impeded by pressure , especially if the muscles of
inspiration are weak : because pressure increases with density of fluid as well
as with the depth.
- Deep immersion of a patient with weakness of these muscles in a high-
density liquid such as saline may prove dangerous.

Depth in the fluid
● At a point well below the surface there is a considerable column of water
above, on which gravity exerts a downward pull, so the pressure at this level
is greater than that near the surface .

15.Density
● It is the relationship between the mass & the volume of a substance.
● Mass is the quantity of material present in a body.
● Volume is the area occupied by a certain mass of material

16.Relative Density(R.D)
● Ratio of the density of the substance to the density of the water.
R.D of water = 1
R.D > 1 = sink
R.D < 1 = float
R.D = 1 = submerged with floating

● Average human body will just float
● Fat & lung tissue → contains air → float
● Relative Density varies with age
Young Adult → 0.85
Adolescent & early adulthood → 0.97 as adipose tissue deposits →
Human body → 0.95
● E.g . Wood R.D = -0.57
Iron R.D = 7.7

● When the body is allowed to float it will do so in the prone position , the rib
cage often just showing above water. This position has its limitations in
therapy.
● Some effort is required in order to float in supine position , the head needs
needs to be slightly extended & the areas abducted . Despite such effort ,
some people will find that their legs will tend to sink & a few others will float in
vertical position.
● Therapist will note that a significant number of patients will need pelvic / leg
floats when required to exercise in the floating position.

Density of fluid
● The density of a substance is its mass per unit volume.
● The greater the mass,the greater is the force exerted by gravity upon it i.e., the
weight.
● so , the weight of a high density fluid is greater than that of a fluid of lesser density ,
and a greater pressure is exerted by it .
● The density of water is 1g/㎤ at 4 ℃( 62.5 lb per cubic foot).
● The density of other substances is assessed by comparison with that of pure water
at 4℃, giving the specific gravity( relative density):
Specific gravity = mass of given volume of a substance
mass of same volume of water

● One ㎤ of water weighs 1 g, while 1 ㎤ of copper weighs 8.9 g , so the
specific gravity of copper is 8.9 .
● Any substance with a specific gravity of more than 1 has a greater density
than water.
● One ㎤ of cork weighs 0.2g, so the specific gravity of cork is 0.2.
● Any substance with a specific gravity of less than 1 has a lesser density than
water , and therefore floats.
● The average specific gravity of the human body without air in the lungs if
1.050-1.084, and with air in the lungs 0.974.

17.Specific Gravity
● Also known as “Relative Density:
● The density of an object relative to that of water
● The density of a substance divided by density of H2
O.
● Specific Gravity = It is the ratio of density of substance or fluid to the density of a reference substance (H2O)
● For eg
Specific density(SD) of H2o = 1.000
SD of Urine = 1.002- 1.030 if kidneys function normally
Specific Gravity = 1.002/1.000
= 1.010
It indicates mild dehydration . The higher the number the more dehydrated

– Specific gravity of water = 1
• If object’s s.g. is > 1, object will sink
• If object’s s.g. is < 1, object will float
• If object’s s.g. is = 1, object will float just below water surface
• S.G. of fat = 0.8
• S.G. of bone = 1.5-2
• S.G. of lean muscle = 1.0
• Human Body = 0.95-0.97 (Less than 1 - enables the body to float)

• Buoyancy is partially dependent on body weight
– Different body parts will vary
– On average, human S.G. is less than water
• Doesn’t mean body will float due to body part make-up
• Factors that determine the specific gravity of the individual body part:
• ratio of bone weight to muscle weight
• the amount & distribution of fat
• depth & expansion of chest
• Air in lungs vs. extremities
• Lungs filled with air can ↓ the specific gravity of the chest (allows head & chest to float higher in the water)

18.Specific Weight (ᵧ)
● Weight of a substance per unit volume
● γ = weight of the body (mg) / volume of the body or material
● SI Unit is N/㎥
● Specific weight of water on earth at 4℃ = 9.807 kilonewtons per cubic metre
● For air at 15℃ if the atmospheric pressure at sea level is 101kPa, specific
weight is 12N/m3

19.Specific Volume (𝜇)
● It is the ratio of substance volume to mass of substance
Specific Volume = substance volume / mass of substance
● Reciprocal of density
● SI Unit is ㎥/kg

20.Capillarity
● It is the rise or depression of liquid in a small passage such as a tube of small
cross-sectional area or like spaces between fibres of towels.
● It is the result of surface or interfacial forces.
● The rise of water in a thin tube inserted in water is caused by forces of attraction
between the molecules of water & glasswalls & among the molecules of water
themselves.
● These attractive forces just balance the force of gravity of column of water that has
risen to a height.
● The narrower the tube , the higher the water rises.
● Mercury does not rise even depressed because there is no attraction of molecules
of mercury with tube

● For capillarity, less than 6mm diameter tube is inserted vertically inside a pool
of liquid , the liquid level in the tube either rise or fall relatively to the liquid
level in the pool.
● This phenomenon of rise or fall of liquid level in the capillary tube is called as
capillarity.

Capillary Rise
Adhesion force > Cohesion force
Liquid Level = concave upward
𝜃 = Acute angle
Capillary Fall
Cohesion force > Adhesion force
Liquid Level = convex upward
𝜃 = Obtuse angle

The magnitude of capillarity is dependent upon
● Diameter of tube
● Speciﬁc weight of liquid
● Surface tension of liquid
Let d be the diameter of the glass tube and θ is the contact angle between liquid and glass tube. The water shall rise in the
tube till vertical component of surface tension equals the weight of the water column.
The surface tension force acting around the circumference of the tube = σ x πd.
The vertical component of this force = σ x πd x Cosθ ————(i)
Rise of the water in the tube (i.e. height) = h
The weight of the liquid column of height h in the tube = Area of the tube x h x Speciﬁc weight

21.Buoyancy
● Buoyancy is the upward force that works opposite to gravity.
● Upward force that works opposite to gravity
● Counterforce that supports submerged or partially submerged object against pull of gravity
● Assists motion toward water’s surface
● According to Archimedes Principle
“ an immersed body experiences upward thrust equal to the volume of liquid displaced .”
● Archimedes Principle states that any body which is wholly or partially immersed will experience an upward thrust equal to the weight of fluid
displaced. This upward thrust is termed the force of buoyancy,it acts through a point called the centre of buoyancy. This centre need not
coincide with centre of gravity.
● The human body will seem ‘lighter’ when wholly or partially submerged.
● Buoyancy provides the patient with relative weightlessness and joint unloading , allowing performance of active motion with increased ease .
● Buoyancy allows the practitioner three -dimensional access to the patient .
● Hydrotherapy can be used in this position. It both allows the patient to be easily maneuvered by the therapist & facilitates then movements &
postures.

– Sense of weight loss (equal to amount of water that is dissipated)
• Changes relative to level of submersion
• Differing levels in males & females due to relative CoG
– Allows for ambulation & vigorous exercise with little impact & friction reduction
between articular surfaces

❏ This results from the relative density of the body, or body part, and the higher density of water.
❏ Buoyancy results in an apparent loss of weight of the object when placed in the water and it may be used to either
assist or resist movement.
❏ Buoyancy will be of particular advantage in reducing the effect of gravity on the body, particularly on load-bearing
joints such as lower back, hips and knees.
❏ Buoyancy may increase the function or the range of movement that is possible, for example hip and knee flexion in
standing.
❏ It may also be utilised to increase range of movement as a mobilising exercise, an effect that can be further
enhanced by the use of a float or inflatable wrist or ankle bands, for example to mobilise shoulder flexion with a wrist
float in sitting.
❏ Buoyancy can also be used in strengthening exercises.
❏ Buoyancy-resisted exercise involves pushing against buoyancy. The effect can be increased by again adding floats,
for example hip extension while floated in supine against an ankle float.
❏ As the exercises are progressed, the inflatable bands can be further inflated or, alternatively, the position of the float
on the lever can be adapted therefore changing the buoyancy effect on the limb, i.e. the effect will be increased with
a distal float placement.
❏ If buoyancy is to be counterbalanced the patient will need to exercise along the pool surface.
❏ The greater the buoyancy of the float the greater the mobilising effect of the exercise. These types of exercise are classed as
buoyancy-assisted.

● A buoyant body has a density less than that of the liquid in which it is
immersed, and so tends to rise to the surface .
● This is due to the vertical upward pressure that the liquid exerts on such a
body.
● At any one point water exerts an equal force in all directions,but this force
increases with depth.
● The lower part of an immersed object is at a greater depth than the upper part
, so the pressure exerted by the water on the lower part is greater than that on
the upper part .
● Thus the pressure of the water exerts an upward acting force on the object
which is greater than that which it exerts in a downward direction.
● For a body denser than water, the weight of the body more than balances this
upward thrust , and the body sinks.

● A body less dense than water has not enough weight to balance the upthrust ,
which therefore tends to raise the object towards the surface of the water .
● The force acts at the centre of buoyancy of the object , which is same point as
the centre of gravity of the fluid displaced by the object.

Center of Buoyancy
● Center of buoyancy, rather than center of gravity, affects the
body in an aquatic environment.
● The center of buoyancy is the reference point of an
immersed object on which buoyant (vertical) forces of fluid
predictably act.
● Vertical forces that do not intersect the center of buoyancy
create rotational motion.

● Center of buoyancy is the center of gravity of the displaced fluid and the point at which the
buoyant force acts on the body.
● In water, two opposing forces act on the body. Buoyancy is the upward force, and gravity is
the downward force.
● Each has a center point of balance.
● When a floating body is in equilibrium, the center of buoyancy and the center of gravity are in
vertical alignment with each other (figure 10.1).
● In this position, the body is balanced.
● If the center of buoyancy and the center of gravity are not in vertical alignment with each
other, the body is out of equilibrium and will tend to roll or turn.
● For example, if you place a kickboard between your knees, the center of buoyancy will cause
your lower extremities to move upward to float.

Moment of Buoyancy
● If floating body is to remain in a position of equilibrium, the centre of buoyancy
& gravity must lie in same vertical line.
● When they are not in line a turning force or couple is produced, the body
moving toward a position of equilibrium. This turning force is known as
moment of buoyancy .
● Eg:Taking the head backwards will produce a moment which will lead to
lying;bending the head forwards will allow the patient to stand again.

Figure 10.1 When the center of buoyancy and the center of gravity are not in vertical alignment, a person must actively work to keep from rolling in the water.
(a) The body is in equilibrium; the centers of gravity and buoyancy are aligned vertically.
(b) The body is not in equilibrium; the centers of gravity and buoyancy are not aligned vertically.

● In the vertical position , the human center is located at the sternum.
● In the vertical position, posteriorly placed buoyancy devices cause the
patient to lean forward; anterior buoyancy causes the patient to lean back.
● During unilateral manual resistance exercises the patient revolves around
the practitioner in a circular motion.
● A patient with a unilateral lower extremity amputation leans toward the
residual limb side when in a vertical position.
● Patients bearing weight on the floor of the pool (i.e., sitting, kneeling,
standing) will experience aspects of both the center of buoyancy and center
of gravity.

Hydromechanics
● Hydromechanics comprise the physical properties and characteristics of fluid
in motion.
Components of flow motion
❏ Laminar Flow
❏ Turbulent Flow
❏ Drag

Fluid Flow Patterns
● The type of flow pattern developed in a fluid depends on three major factors:
1) Velocity of flow
➔ The velocity of flow of a fluid is the speed at which it moves .
2) Viscosity of the fluid
➔ Viscosity is the internal resistance of a fluid to any change . It is due to friction
occurring between the individual molecules of the liquid
3) Shape
➔ The shape of the container through which the fluid moves will affect its flow pattern.
The shape of the object moving through water which also affect the flow in the fluid
lying in the near of the body .

Laminar Flow
● Movement where all molecules move parallel to
each other , typically slow movement.
● Water molecules move from a point of higher
pressure to one of lower pressure.
● In laminar flow these molecules form layers which
slide over one another a streamlined manner.
● The path of the molecule is in the same line as
that of general flow.
● Viscous friction occurs between these adjacent
layers , impeding the flow of the fluid.
● The greater the viscosity of fluid , the greater will
be impediment & thus slower the flow.
● Laminar flow only occurs with low velocity fluid
movement & it will therefore be seen that fluids of
higher viscosity have a greater tendency towards
Laminar flow.

Streamlining
● This refers to the surface area of the body part exposed to the water when moving
through it.
● The simplest example is the orientation of the upper limb during exercise.
● If the hand moves with the palm facing the resistance of the water more effort is
required than when the limb is rotated so that the ulnar border leads.
● Moving from streamlined to non-streamlined positions can be used to progressively
strengthen.
● This principle can be further progressed by the use of hand-held bats or by placing
flippers on the feet.

Turbulent Flow
● Movement where molecules do not move
parallel to each other, typically faster
movements.
● When an increase in flow rate the laminar
pattern will break up & turbulence will
occur , the molecules no longer travel in
layers but take on an irregular pattern of
motion
● Turbulence creates an unstable
environment encouraging the core
muscles of the body to become stronger to
maintain correct position and posture.

Turbulence
● As limbs move through water they meet resistance and turbulence is created, resulting in the
production of currents.
● Turbulence results in an area of low pressure behind the moving body or body part.
● Faster movements will produce more turbulence.
● These currents may act to make movement more difficult and so this principle is of value
when progressing an exercise, for example if exercises are performed rapidly more
turbulence will be created and will prove more difficult to move though.
● Also, therapist- created turbulence can be used in re-education of movement, particularly in
the weight-bearing muscles of the lower limb.
● The client is subjected to turbulence during standing and must maintain their position.
● This can prove very difficult and can be quite an advanced exercise.

● 3 Resistive forces work in
water
○ Cohesive force
○ Bow force
○ Drag force
■ Form Drag
■ Wave Drag
■ Frictional Drag
Bow force
– Force generated at front end of
object during movement
• When object moves, ↑ in
water pressure at the front
and ↓ pressure in the rear
• Creates a pressure gradient,
resulting in low pressure
zones swirling = eddies
(turbulence) create a drag
force

Drag
● water’s resistance to movement within a fluid that is caused by the friction of the
fluid’s molecules
● The cumulative effects of turbulence and fluid viscosity acting on an object in
motion.
● Drag is the water’s resistance to a body that is moving through it.
● The three types of drag are
A. form drag,
B. wave drag, and
C. frictional drag

• Can be changed by shape and speed of object
• ↑ streamline = ↓ drag
• Must be considered carefully when attempting to protect a limb during rehabilitation
• Drag forces can ↑ torque at a given joint which may be contraindicated

● As the speed of movement through water increases, resistance to motion
increases.
● Moving water past the patient requires the patient to work harder to maintain
his/her position in pool.
● Application of equipment ( glove/paddle/boot)increases drag and resistance
as the patient moves the extremity through water .

Form Drag
● resistance that an object encounters in a fluid and is determined by the object’s
shape & size
● Form drag is the resistance that an object encounters in a fluid.
● The amount of form drag is determined by the object’s size and shape.
● A larger object has more drag than a smaller object. A broad object has more drag
than a streamlined object.
● Form drag is directly related to turbulence.
● The greater the form drag, the greater the turbulence.
● Turbulence produces a low-pressure area behind the object that tends to pull the
object backward, like what is seen behind a speedboat moving on a lake (figure
10.2).

Figure 10.2 Form drag: (a) laminar flow (which produces minimal form drag) and (b)
turbulent flow. Form drag is caused by turbulence behind an object moving through a fluid.

● A streamlined object moving through water produces a laminar flow—a smooth movement of water that causes a
minimal amount of resistance.
● There is less form drag because there is less turbulence.
● The water molecules all travel at the same speed past the moving body. Friction of the fluid is minimal because the
water molecules separate easily, moving smoothly behind the object.
● On the other hand, a broad object produces a turbulent flow as it moves through the water.
● The object has more form drag because of the greater turbulence created behind it.
● The layers of the water move irregularly as they run into the object and rush to move past and behind it.
● This causes a circular movement of the water layers as they rejoin behind the object.
● This circular motion of water layers pulling against the moving object is called an eddy.
● In essence, the turbulence creates a backward pull on the forward-moving object, adding to the effort the object
must make to move through the water.
● Because of the disturbance caused by the eddy, a wake, or trail, is left in the water (seen as either bubbles behind
the body or white water, depending on the amount of turbulence created).

● Form drag can be used in an aquatic therex program as a means of altering resistance to
exercises.
● A change in the position of the body or body segment can increase or decrease form drag.
● For example, moving the arm horizontally in the water with the palm down causes less
form drag than with the hand in a vertical position.
● Shortening or lengthening the body’s extremity decreases or increases the form drag,
respectively, since a longer lever arm pushes more water than a shorter one.
● Adding equipment such as hand paddles increases the surface area of the hand, and
adding long paddles increases the lever-arm length; both provide additional form drag to
increase the resistance of an exercise.

Wave Drag
● water’s resistance as a result of turbulence
● Wave drag is the water’s resistance because of turbulence caused primarily by the speed of the object in the water.
● The greater the speed of the object, the greater the wave drag.
● Wave drag is reduced if movement remains underwater because less wake is produced.
● The amount of water wake is an indication of wave drag. Swimming pools often have a splash gutter around the periphery to reduce
wave drag for swimmers.
● Exercises performed in calm water produce less resistance than those performed in turbulent water.
● The person can create wave drag during an exercise by changing positions often and rapidly. Increasing the speed of an exercise also
increases the wave drag, thereby increasing the exercise’s resistance.
● For example, walking in water provides the body with 5 to 6 times the resistance that walking in air does. Running in water, however,
increases the resistance to more than 40 times that of air.

Frictional Drag
• result of water’s surface tension
• Frictional drag is the result of water’s surface tension.
• This is not a factor in rehabilitation, but it becomes an important element for competitive swimmers.
• Frictional drag can add crucial milliseconds to a race time; swimmers reduce frictional drag by
shaving body hair before competition.
• Recently, custom-made bodysuits constructed from unique new fibers have reduced frictional drag.

Eddy Formation
● An eddy or back current , is an exaggerated turbulent pattern which can arise in either laminar or
turbulent flow.
● Eddies arise at points of change in shape in containers or follow the movement of a body through
fluid .
● An area of reduced pressure forms downstream of irregularity & back currents flow into these areas
forming eddies.
● Such eddies following a moving body may be termed as a wake. It give rise to a drag which will
impede the movement of object .
● Eg ; Therapist makes considerable use of these factors when treating patients in water. Slow
movement of patient through the medium facilitates laminar flow of the water & consequently there
is less resistance to movement.

● Further reduction in eddy formation may be achieved by presenting the most
streamlined aspect of the body to the water. Thus it will be found that waking
sideways(slowly) through the water is much easier than waking forward
(quickly).
● Use may be made of resistance offered by the water.

The Law of Floatation states that a floating body displaces its own weight of the
fluid in which it floats.
Conditions for a body to float: The conditions that a body will float in a fluid are
listed below.
The density of the fluid in which the body is immersed should be greater than that
of the body itself.
The upthrust force exerted by the fluid on the lower surface of the body must be
equal to the weight of the body.
The volume of the body should be large enough to displace a large amount of
fluid.

Thermodynamics
● Water temperature has an effect on the body and, therefore, performance in
an aquatic environment.
❏ Specific heat
❏ Temperature transfer

Specific Heat
● Specific heat is the amount of heat ( calories) required to raise the
temperature of 1gm of substance by 1℃.
● The rate of temperature change is dependent on the mass and the specific
heat of the object.
● Water retains heat 1000 times more than air.
● Differences in temperature between an immersed object and water equilibrate
with minimal change in the temperature of the water.

Temperature Transfer
● Water conducts temperature 25 times faster than air.
● Heat transfer increases with velocity.
A patient moving through the water loses body temperature faster than an
immersed patient at rest.

Aquatic Temperature & Therapeutic Exercise
● A patient’s impairments and the intervention goals determine the water
temperature selection.
● In general, utilize cooler temperatures for higher-intensity exercise and utilize
warmer temperatures for mobility and flexibility exercise and for muscle
relaxation.
● The ambient air temperature should be 3°C higher than the water
temperature of patient comfort.
● Incorrect water or ambient air temperature selection may adversely affect a
patient’s ability to tolerate or maintain immersed exercise.

Temperature Regulation
● Temperature regulation during immersed exercise differs from that during land
exercise because of alterations in temperature conduction and the body's
ability to dissipate heat. With immersion there is less skin exposed to air,
resulting in less opportunity to dissipate heat through normal sweating
mechanisms.
● Water conducts temperature 25 times faster than air—- more if the patient is
moving through the water and molecules are forced past the patient.
● Patients perceive small changes in water temperature more profoundly than
small changes in air temperature.

● Over time , water temperature may penetrate to deeper tissues .
Internal temperature changes are known to be inversely proportional to
subcutaneous fat thickness.
● Patients are unable to maintain adequate core warmth during immersed exercise at
temperatures less than 25℃.
● Conversely , exercise at temperature greater than 37℃ may be harmful if prolonged
or maintained at high intensities.
Hot water immersion may increase the cardiovascular demands at rest and with
exercise.
● In waist- deep water exercise at 37℃, the thermal stimulus to increase the heart rate
overcomes the centralization of peripheral blood flow due to hydrostatic pressure.
● At temperatures greater than or equal to 37℃, cardiac output increases significantly
at rest alone.

Mobility and Functional Control Exercise
● Aquatic exercises,including flexibility,strengthening,gait training, and
relaxation, may be performed in temperatures between 26℃ and 33℃.
● Therapeutic exercise performed in warm water (33℃) may be beneficial for
patients with acute painful musculoskeletal injuries because of the effects of
relaxation, elevated pain threshold, and decreased muscle spasm.

Aerobic Conditioning
● Cardiovascular training and aerobic exercise should be performed in water
temperatures between 26°C and 28°C .
● This range maximises exercise efficiency, increases stroke volume, and
decreases heart rate.
● Intense aerobic training performed above 80% of a patient’s maximum heart
rate should take place in temperatures between 22°C and 26°C tominimise
the risk of heat illness.

Apparent loss in weight
● When an object is immersed in a fluid there are opposing forces acting upon
it .
● Gravity tends to pull it vertically down , the magnitude of the force depending
on the mass of the object and determining its weight.
● Buoyancy due to the upthrust of the fluid , tends to move the object vertically
up , in opposition to the force of gravity.
● The upthrust exerted by the fluid subtracts from the downward acting force so
the object undergoes an apparent loss in weight:
The downward force is reduced by an amount equal to the magnitude of the
upward force .

● The upward force, which previously supported the fluid displaced by the
object, is equal to the weight of fluid displaced.
● So the apparent loss in weight of the immersed object is equal to the weight
of fluid displaced.
● The Principles of Archimedes states that when when a body is wholly or
partially immersed in a fluid at rest, it experiences an apparent loss in weight
equal to the weight of the fluid displaced.
● The behaviour of a body immersed in a fluid is determined by the balance
between
❏ the downward pull of gravity and
❏ The upthrust of the fluid

● An object with a specific gravity of 1 and a volume of 1 weighs 1g.
● Such an object, when fully submerged in water, displaces 1 of water which
weighs
● So the force of upthrust of buoyancy is 1g wt , which exactly balances the
downward pull of gravity.
● Thus an object with a specific gravity of 1 ‘floats’ fully submerged in water, i.e.
it stays where it is put , in still water.

● An object with a specific gravity of less than 1 and a volume of 1㎤ weighs less than
1g.
● One ㎤ of cork weighs 0.2g.
● If the cork is immersed in pure water, when 0.2㎤ of it is submerged 0.2㎤ of water
has been displaced, so an upthrust of 0.2g wt is exerted on the cork, which
balances the downward pull of gravity.
● The cork therefore floats with 0.2 of its volume submerged, the remaining 0.8 above
the surface.
● An object with a specific gravity of less than 1 floats partially submerged, the
proportion submerged depending on its specific gravity.
● If such an object is fully immersed, the weight of water displaced and so the upthrust
exerted upon it is greater than the weight of the body, so the object rises towards the
surface of the water.

● The human body with air in the lungs has a mean specific gravity of 0.974, so
tends to float in pure water with 0.974 of its volume submerged, the remaining
0.026 above the surface.
● If the body is to remain in the water for more than a short period of time the
unsubmerged part must include the nose or mouth to enable air to be drawn
into the lungs.
● Lifting a limb from the water brings another part of the body out of the water
so that the head is liable to go below the surface.

● An object with a specific gravity of more than 1 and a volume of 1㎤ weighs
more than 1g.
● One ㎤ of copper weighs 8.9g.
● If such an object is fully submerged in pure water it displaces 1㎤ , i.e. 1g, of
water.
● This gives an upthrust of 1g wt.
● The downward force is reduced by this amount, to 7.9g wt, so the object
undergoes an apparent loss in weight, but still sinks.
● An object with a specific gravity of more than 1 sinks, but with apparent loss in
weight.
● The human body without air in the lungs has a specific gravity of more than 1
and so tends to sink in pure water.

Factors determining Upthrust
The Specific Gravity of the Object
● The less the specific gravity, the greater is the effect of the upthrust.
● The specific gravity can be reduced by attaching floats to the object.
● These consist of inflated bags of rubber or pieces of material of low specific
gravity such as cork or polystyrene.
● They have the effect of increasing the volume of the object with a minimal
increase in mass, so that the overall specific gravity is reduced.

The specific gravity of the fluid
● The behaviour of objects immersed in a fluid with a specific gravity of 1 is
considered above.
● If the specific gravity of the fluid is more than 1 a given volume of the fluid
weighs more than the same volume of pure water, so when this volume is
displaced the upthrust is greater than that resulting from displacement of the
same volume of pure water; hence the greater buoyancy of salt water.

Effects of buoyancy on movement
● When movements of the human body are performed with the part immersed
in a liquid, buoyancy assists any movement vertically upward and resists any
movement vertically downward.
● The results of this depend on the specific gravity of the part of the body
relative to that of the liquid in which it is immersed.
● If the part of the body has a specific gravity less than that of the liquid, the
upthrust exerted when it is fully submerged is greater than its weight, so it
tends to float upward without any muscle action, while concentric muscle
contraction is necessary to produce a movement vertically down. The Muscle
action is the opposite to that of the same movement performed in air.

● If the part of the body has a specific gravity greater than that of the liquid, the
upthrust of buoyancy is less than the weight ,so the part sinks, but with apparent
loss in weight. The direction of the movement is the same as in air,so the muscle
work is of similar type. Concentric muscle contraction is necessary to produce a
movement upward and eccentric muscle action is necessary to control a movement
downward. The strength of the muscle action required is,however,less than that
needed in air, owing to the apparent loss in weight.
● Thus buoyancy can be used to provide assistance or resistance to movements, but
it is important to realize that the muscle work of a movement performed in water is
always different in manner or strength from that of the same movement in air, so that
although performing a movement in water may be a valuable method of exercise, it
cannot re-educate a movement for performance in air.

Moment of force
● Many of the movements of the human body are rotary ones of a bone at a joint, and
the efficacy of any force in producing such a movement depends on its moment.
● If the force is the upthrust of the liquid,the perpendicular distance from the pivot to
the line of action of the force depends on the distance of the centre of buoyancy
from the moving joint.
● When the elbow is straight the centre of buoyancy of the upper limb is further from
the shoulder than when it is bent, so the effect of the upthrust is greater .
● Attaching a float to the distal part of a limb moves the centre of buoyancy distally
and further increases the moment of force of the upthrust.

● The distance from the pivot of the line of action of the force also depends on
the position of the part in the water.
● Buoyancy acts vertically upwards, while an object that is turning on a pivot
moves through the arc of a circle.
● Thus it is only when the part is horizontal that the upthrust is acting exactly in
the direction of movement and is fully effective.
● Nearer to the vertical position the upthrust is less effective.
● As the upper limb is raised from the side of the body to shoulder level the
effect of upthrust on it increases, reaching its maximum when the limb is in
the horizontal position.

Effects of apparent loss in weight
● The apparent loss in weight of an object immersed in water makes it easier to lift a heavy object in
water than in air and also easier to maintain the upright position of the human body.
● It does, however, make the body less stable, as the weight normally provides a means of fixation,
and if a patient is immersed in the upright position in deep water he may find it difficult to control his
body.
● In addition, the lack of fixation for the origins of muscles, normally provided by the weight of the
party from which they arise, may make strong muscle work difficult.
● Artificial fixation, such as straps, can be used to compensate for the lack of stability, or the weight
may be increased, eg., by the use of weighted sandals.
● When a part of the body is removed from the water the effects of the upthrust are lost.
● This increase in apparent weight offers appreciable resistance to the removal of the part from the
water.
● The Effect of buoyancy in counteracting the downward pull of gravity can be used to help support a
part of the body during movement ,as an alternative to slings or a supporting surface.
● The specific gravity of every part of the body is close to 1.

Equilibrium of a floating body
● The force of gravity acts on a body at its COG, that of buoyancy at its center
of buoyancy.
● Gravity acts vertically downward and buoyancy vertically upward , so for the
two to oppose each other and the body to remain at rest, the centres of
gravity and of buoyancy must lie in the same vertical line .
● If this does not occur , the floating body rotates until the two centres are in the
same vertical line, with the Centre of gravity below the center of buoyancy.
● If the COG is low the tendency is for the object to right itself after
displacement , while if it is high the object tends to roll over into a new
position , its state of equilibrium being less stable.

● The human body with air in the lungs floats .
● Learning to float while still breathing involves learning to balance the body
with the center of buoyancy and the center of gravity in the same vertical line
and with the appropriate part of the body unsubmerged .
● Any factor which displaces the centre of buoyancy or that of gravity may
interfere with the ability to float in an acceptable position .
● The use of floats may raise the centre of buoyancy , so reducing the stability
of equilibrium , or shift it to one side so that the body tends to roll over.
● Paralysis of one side of the body may have a similar effect in shifting the
centre of buoyancy to one side.

Movement of Water
● Motion of fluids is a subject of great complexity, but the elementary principles
relevant to physiotherapy are considered below .

Fluid Flow
● A flow of water may be streamlined, i.e., a continuous steady movement in which thin layers of
molecules slide over each other .
● The layers in the centre of the stream move fastest while those at the edges are stationary, and the
frictional resistance is proportional to the velocity.
● As the speed of movement of a fluid increases, its pressure gets less.
● This can be demonstrated by placing two books on a flat surface a short distance apart and a sheet
of paper across the gap between them, as in Fig 8.4.
● On blowing air through the gap it is seen that as the speed of the air increases the paper is sucked
down into the area of low pressure.
● When the speed of movement of the water increases to a certain critical velocity, the pressure is
reduced to such a level that water is sucked into the area of low pressure behind the main flow and
forms circular eddy currents.
● The flow is then termed turbulent and the frictional resistance to flow is increased, being proportional
to the square of the velocity.

Inertia
● Water, in common with all matter, has the property of inertia,so some force is
required to start its movement or to stop it or to change the speed or direction
of movement.
● Water is also virtually incompressible,so when an object moves in water, the
water must either part to allow the object to pass or move with it.
● In either case the inertia of the water must be overcome.

Movement of Objects in Water
● If an object moving through water is streamlined, the water parts easily to allow it to pass and flows
in readily behind it, offering little resistance to the movement.
● This occurs if the hand is moved horizontally through the water with the palm directed downwards.
● If the object has a broad surface facing in the direction of movement, as when the hand is held palm
forwards and moved horizontally,the water tends to pile up in front of it.
● This impedes the movement but gives a relatively fixed point from which to obtain the necessary
thrust for propulsion of the body through the water; when rowing, the blade of the oar must be
vertical for this reason.
● If it is horizontal it moves easily through the water and gives no fixed point, and the rower ‘catches a
crab’.
● If the object with a broad leading surface is to move through the water it must either thrust the water
out of the way or move the water with it.
● In either case the inertia of the water must be overcome, and it offers considerable resistance.

● If the object has a broad rear surface it is difficult for the water to flow in
behind it and an area of low pressure is formed.
● This impedes the forward movement of the object,but anything lying in the
area of low pressure will be drawn forward with it.
● A mother duck ‘tows’ her ducklings when they follow her in line astern,and in
most methods of life-saving the rescuer needs only to support the victim,who
is drawn forward in the area of low pressure.
● There is a tendency, however, for the water to be drawn into this area of low
pressure, setting up Eddy currents, so that the flow becomes turbulent and
frictional resistance is increased, further impeding movement.

● Once the water is in motion, an immersed object tends to move with it,and stopping the
movement of the object or altering the speed or direction of its movement will necessitate
doing the same to the water.
● The water has appreciable inertia and so tends to continue a movement which has been
established.
● Once a part of the body is moving with the water little effort is required to continue the
movement at the same speed and in the same direction.
● In order to stop the movement or to change its speed or direction the inertia of the water
must be overcome and a considerable effort is necessary to do this.
● For this reason it is usually easier to perform movements slowly than quickly in water,and
strong muscle work may be required to stop a movement or to change its direction.
● Thus movement of the water may be used to provide either assistance or resistance to
movements of the human body.

PHYSIOLOGICAL EFFECTS OF HYDROTHERAPY
A:Cleansing eﬀects
■Pressure (force = Rate of flow) to remove debris
●Water can be used as a cleanser because it can dissolve and soften materials
and exert pressure
●Hydrating eﬀects and friction of water are used to soften and remove debris that
is lodged in the wound or adhered to the tissue.
■Dissolved surfactants and antimicrobials in water(Wounds) can increase cleansing power
●Surfactants (i.e., soap or detergents) reduce surface tension and thereby reduce
the adhesion of debris to the tissue
●Antimicrobials reduce the microbe count in the water and on the wound's
surface.
■Important to cleanse wounds because necrotic tissue and high concentrations of
microorganisms delays wound healing

B.Musculoskeletal eﬀects
■Decreased weight-bearing (assistive)
● Arthritis
● 75% immersion ↓ WB 75%
●Less weight is placed on LE
○Patients with load-sensitive joints can perform exercises with less trauma and
pain.
●E.g. in OA patients, reduced WB leads them to walk in the pool w/o feeling any
symptoms
●Can help patients with arthritis, ligamentous instability, cartilage breakdown, or
other degenerative or traumatic conditions of the articular or periarticular
structures of the weight-bearing joints
●Can also help obese patients who have more low-density, subcutaneous fat than
average weight people, they are more buoyant in water
○Water-based activities reduce their joint loading even more.

● Off loading weight - Range of Motion activities, gentle strength building , and
even gait training.
● Resistance by buoyancy/ viscosity -strengthening
● CKC/OKC
○ Closed Kinematic Chain
○ Open Kinematic Chain
● Less joint stress – GRF less, more time taken
○ Ground Reaction Force
● More blood – supply less fatigue
● Increases blood flow to muscles

Strengthening (resistive)
●Move against buoyancy for resistance
○Velocity-dependent resistance provided by water can be used to provide a
force against which muscles can work to gain or maintain strength
●Ex. adducting the arm
■Eﬀects on bone density loss
● Decreased bone density loss
●Wolﬀ's Law → strengthening of bones
○“Bones will adapt based on the stress or demands placed on them.”
■Less fat loss (vs other exercises)
● Decreased fat loss
○ Compared to other forms of exercise
● Good for obese secondary to non - weight bearing exercise
○ Not good for general weight loss

C.Thermal effects(Thermoregulation)
COLD WATER HOT WATER
● Decreases metabolism
● Pain relief
● Controls inflammation
● Slowed HR initially
● HR returns to baseline in 10 min
● Stroke Volume increased
● Cardiac output remains same
● Relaxes muscle
● Increases flexibility
● Improves circulation
● Increases tissue extensibility
● Pain relief
● HR is increased
● Increased cardiac output
● Rise in core temperature
● Muscle blood flow increased

D.Cardiovascular eﬀects (domino eﬀect)

● Submersion to the neck increases cardiac output by more than 30%.
● Diminished sympathetic vasoconstriction produces peripheral venous
pressure decrease by 30%.

■Primarily a result of hydrostatic pressure.
■ ↑ Venous circulation (return)
● Secondary to hydrostatic pressure, increased venous pressure
● Higher hydrostatic pressure compresses veins on distal UE which
allows faster blood return
■ ↑ Cardiac volume
●Allows more blood to go to the heart
●The increase in cardiac volume increases right atrial pressure by 14 to 18
mmHg,to which the heart responds, according to Starling's law, with an
increase incontraction force and stroke volume

■ ↑ Cardiac output and stroke volume
●Amount of blood pumped by the heart per minute
●Each time the heart pumps, more volume of blood is sent out
●Results in approximately 30% increased cardiac output over baseline in response
to upright immersion up to the neck(upto 30% while upright to neck)
■ ↓ Heart rate
●Chemoreceptors and baroreceptors sense adequate amount of blood, it signals a
decrease in heart rate
●When a person exercises in water, the heart rate response is blunted. Therefore
perceived exertion (RPE Scale) rather than heart rate should be used to guide
exercise intensity
■ ↓ Systolic BP
■ ↓ Rate of O2 uptake (VO2)

E.Respiratory eﬀects
■ ↓ Vital capacity
●Increased hydrostatic pressure,limited chest expansion/increases resistance to lung expansion
○Compression of chest wall
■ ↑ Work of breathing
● Due to hydrostatic pressure on lungs
○ Upto 60%
○ May need to be very careful with respiratory &/or cardiac patients
● Increased circulation to chest cavity = lungs need to cope up with adequate amount of blood in
the lungs
● Shift of venous blood from the peripheral to the central circulation
● Can be used to improve the eﬃciency and strength of the respiratory system
■ ↓ Exercise-induced asthma
●High humidity of air → decreased chance of exacerbating asthma
○Prevents drying or cooling of the respiratory mucosa

F.Renal effects
■ Increases urine production( Diuresis)
●Urinate more frequently
● ↑ renal blood flow
■ ↑ Na+ & K+ excretion
●Increased hydrostatic pressure,increases blood supply to kidney,increases passage and formation of urine
● May be used to patient’s advantage with hypertension,peripheral edema
■ ↑ Central blood volume
●Hydrostatic pressure → Concentrate blood to central portion of the body →decrease release of aldosterone and antidiuretic
hormone (ADH) → trigger increase in production of urine
■ ↓ Edema: Both reduces edema as fluids are released
■Can be taken advantage to treat patients with hypervolemia, hypertension, or
peripheral edema.
■Particularly an effect of cold immersion

G.Psychological eﬀects
❏ Relaxing (warm water),
❏ energizing/invigorating (cool water)
●Warm water: comforting and calming environment for overstimulated or agitated
patients
○Warm whirlpools are often used to facilitate motion and exercise (e.g.
stretching of contractures) for subacute and chronic stages of sprains and
Strains.
●Cold water: facilitate more active exercise participation by patients who are
generally less active or responsive
○Cold whirlpools are typically used to help control pain and swelling of acute
sprains and strains.

Therapeutic Effects
● Relieve pain and muscle spasm
● To gain relaxation
● To maintain or increase the range of joint movement
● To re-educate paralyzed muscles
● To strengthen weak muscles and to develop their power and endurance.
● To encourage walking and other functional and recreational activities.
● To improve circulation ( trophic condition of the skin )
● To give the patient encouragement and confidence in carrying out his exercises, thereby improving his
morale.
● The warmth of water blocks nociception by acting on thermal receptors and mechanoreceptors, thus
influencing spinal segmental mechanisms.
● Warm water stimulates blood flow positively, which leads to muscle relaxation.
● the hydrostatic effect may relieve pain by reducing peripheral oedema and by dampening the
sympathetic nervous system activity.

Contraindications and Precautions
● Contraindications and precautions are important when considering
patients for any exercise programme and more so with hydrotherapy
owing to potential emergency evacuation situations.
● This is mainly because of the warm environment in which they are
exercising and the dangers of slipping or drowning.

Contraindications include
● the presence of certain medical conditions such as
○ recent, or severe, neurological conditions (including uncontrolled epilepsy),
○ certain cardiovascular problems and kidney failure.
● Hydrotherapy is also contraindicated with debilitating disease and the presence of
infections which may be exacerbated or risk transmission to other patients.

Contraindications
Serious
● Cardiovascular/cardiopulmonary disease
● Diabetic
● Balance disorder
● History of CVA, Epilepsy
● Incontinence
● Labyrinthitis
● a cold
● Influenza
● Fever
● skin conditions
● Chemical allergies (Chlorine)
Absolute
● Contagious diseases
● Hepatitis
● Tracheotomy
● Urinary tract infection
● Serious Epilepsy
● Urinary incontinence
● Open Wounds
● Recently Surgery
● Hydrophoby

SPECIAL EQUIPMENT FOR AQUATIC EXERCISE
● A large variety of equipment exists for use with aquatic exercise.
● Aquatic equipment is used to provide buoyant support to the body or an
extremity, challenge or assist balance, and generate resistance to movement.
● By adding or removing equipment , the practitioner can progress exercise
intensity.

• Facility must have certain characteristics
– Should be at least 10 x 12
– Adequate access
– Shallow and deep areas
– Flat pool floor with marked gradients
– Adequate temperature (26-28degrees)
• Ancillaries
– Prefabricated pools with treadmill or other device
– Pool toys , sports equipments

❏ Collars , Rings, Belts , and Vests
❏ Swim Bars
❏ Gloves, Hand Paddles , and Hydro-Tone Balls
❏ Fins and Hydro-Tone Boots
❏ Kickboards

Collars, Rings, Belts, and Vests
● Equipment designed to assist with patient positioning by providing buoyancy assistance can be applied to the neck, extremities, or trunk.
Inflatable cervical collars are used for the supine patient to support the neck and maintain the head out of the water .
● Flotation rings come in various sizes and are used to support the extremities in any immersed position .
● Often the rings are used at the wrists and ankles during manual techniques to assist with patient positioning and relaxation. Several types of
belt exist that may be used to assist with buoyancy of an extremity or the entire body).
● Belts and vests are used to position patients supine, prone, or vertically for shallow and deep water activities.

1.Inﬂatable cervical collars
■Support neck; maintain head out of water

2.Floatation rings
■Support extremities (UE and LE)
■Wrists, ankles

4.Swim Bars or Buoyant dumbbells
● Buoyant dumbbells( Swimbars) are available in
short and long lengths.
● They are useful for supporting the upper body or
trunk in upright positions and the lower extremities
in the supine or prone positions.
● Patient’s can balance city (seated or standing)
on long swimbars in deep water to challenge
Balance, proprioception, and trunk strength.

5.Gloves,Hand Paddles, and Hydro-tone Balls
● Resistance to upper extremity movements is
achieved by applying webbed gloves or
progressively larger paddles to the hands.
● These devices are not buoyant and,therefore only
resist motion in the direction of movement.
● Hydro -Tone Bells are large,slotted plastic devices that increase drag during upper
extremity motions.
● The bells generate substantially more resistance than gloves or hand paddles.

6.Fins and Hydro-Tone Boots
● The application of fins or boots to the feet during
lower extremity motions generates
resistance by increasing the surface area
moving through the water .
● Fins are especially useful for challenging
hip,knee, and ankle strength.
● Hydro -Tone Boots are most effective during
deep water walking and running

7.Kickboards
● The shape and styles of keyboard is vary
extensively among manufacturers.
● Nevertheless ,Kickboards remain a
versatile and effective aquatic tool for
augmenting any exercise program.
● Kickboards may be used to provide
Buoyancy in the prone or supine
positions, create resistance to walking
patterns in shallow water when held
vertically,or used to challenge seated,
kneeling, or standing balance in the deep
water.

Aquatic Techniques
• Must consider
– Type of injury/surgery
– Treatment protocols if appropriate
– Results/muscle imbalances found in evaluation
– Goals/expected return to activity
• Program design
– Warm-up
– Strengthening/mobility activities
– Endurance/cardiovascular
– Cool down/stretch

Aquatic Rehabilitation: Advantages
• Exercises supported through buoyancy
– Minimizes discomfort
– Sense of security
• Useful in early stages of rehabilitation
– Supportive environment
– Slow motion effect – extra time to control movement
• Proprioception enhancement
– Turbulence provides perturbations and tactile sensory stimulus
• Extremely useful with lower-extremity injuries
– Provides gradual transition from non to full weight-bearing
– May allow earlier locomotion due to decreased compressive forces

Aquatic Rehabilitation: Advantages
• Psychological impact
– Increased confidence due to increased function allowed by water
• Strengthening and muscle re-education
– Dependent on effort put forth by athlete
– Manipulating turbulence, speed , body position and equipments
• Energy expenditure
– Aerobic workout possible to maintain CV fitness

Aquatic Rehabilitation: Disadvantages
• Building and maintaining a rehabilitation pool
– Space and personnel
• Aquatic training may be too challenging if athlete unable to
stabilize body
• Thermoregulation
– May impact tolerance for participation in heat
• Contraindications:
– Open wounds, fear of water, fever, urinary tract infection, allergies to
pool chemicals, cardiac dysfunction or uncontrolled seizures

FLUID MECHANICS AND HYDROTHERAPY

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