Download Cyclic loading and connective tissue fatigue.

Chapter-4
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Creep.
Stress-relaxation.
Cyclic loading and connective tissue fatigue
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load applied for an extended period of time,
the tissue elongates, resulting in permanent
deformation.
related to the viscosity of the tissue and is
therefore time-dependent.
The amount of deformation depends on the
 amount of force and
 the rate at which the force is applied.
Low-magnitude loads, in elastic range and applied
for long periods,
 increase the deformation of connective tissue and
 allow gradual rearrangement of collagen fiber
bonds (remodeling) and
 redistribution of water to surrounding tissues.
 Increasing the temperature of the part increases
the distensibility of the tissue
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When a force (load) is applied to stretch a
tissue, after the initial creep there is a
decrease in the force required to maintain
that length, because the tension in the tissue
decreases
This, like creep, is related to the viscoelastic
qualities of the connective tissue and
redistribution of the water content.
Stress-relaxation is the underlying principle
used in prolonged stretching
Repetitive loading of tissue increases heat
production and may cause failure below the
yield point.
 The greater the applied load, the fewer number
of cycles needed for failure.
 The intensity of the load is determined by the
patient’s tolerance.
 endurance limit.
 minimum load required for that failure.Below
that minimum load an apparently infinite
number of cycles do not cause failure.
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Examples of connective tissue fatigue from
cyclic loading are
 stress fractures
 overuse syndromes.
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Effects of Immobilization
Effects of Inactivity (Decrease of Normal
Activity)
Effects of Corticosteroids
Effects of Age
Effects of Injury
1. Effects of Immobilization
 Tissue weak because of Collagen turnover
and weak bonding between the new, non
stressed fibers adhesion formation
 adhesion formation because of
 greater cross-linking between disorganized
collagen fibers
 because of decreased effectiveness of the ground
substance to maintaining space and lubrication
between the fibers.
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rate of return to normal tensile strength is
slow
Partial and near-complete recovery followed
the same 5-month and12-month pattern.
Decrease in the size and amount of collagen
fibers, resulting in weakening of the tissue.
 proportional increase in the predominance of
elastin fiber
 Recovery takes about 5 months of regular cyclic
loading
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decrease in the maximum tensile strength
rate of adaptation to stress is slower.
increased tendency for overuse syndromes,
fatigue failures, and tears with stretching.
decrease in tensile strength of collagen
 fibrocyte death next to the injection
site with delay in reappearance of fibrocytes
up to 15 weeks.
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Excessive tensile loading can lead to rupture of
ligaments and tendons
Healing follows by synthesized type III collagen.
This is structurally weaker than mature type I
collagen.
begins about 3 weeks post injury and continues
for several months to a year
depending on the size of the connective tissue
struc-ture and magnitude of the tear.
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Alignment
Stabilization:
Intensity of stretch:
Duration of stretch:
Speed of stretch:
Frequency of stretch:
Mode of stretch:
Fundamental components of
 Muscle testing
 Goniometry
 ROM
 Strengthening exercises,
 also affect stretching
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Alignment
Alignment of the muscles and joint to be
stretched
and alignment of the trunk and adjacent
joints
Alignment influences the amount of tension
applied to muscles
Stretching of rectus femoris
 knee is flexed
 hip extended
 the lumbar spine and pelvis should be aligned
in a neutral position.
 The pelvis should not tilt
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To achieve an effective stretch
stabilize either the proximal or distal
attachment of muscle
for manual stretching it is common for a
therapist to stabilize the proximal attachment
and move the distal segment
For self-stretching, distal attachment that is
stabilized as the proximal segment moves
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Sources of stabilization include
manual contacts
body weight
a firm surface such as a table, wall, or floor.
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low intensity
High intensity
Low-intensity stretching in comparison to
high-intensity is more comfortable
minimizes muscle guarding
patient remain relaxed or assist with the
stretching procedure.
coupled with a long duration
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to elongate dense connective tissue more
effectively
less soft tissue damage and post-exercise
soreness than a high-intensity stretch
Interpreting Mechanical Behavior of
Connective Tissue
 Changes in Collagen Affecting Stress–Strain Response
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Effects of Immobilization
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Effects of Inactivity (Decrease of Normal Activity)
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Effects of Corticosteroids
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Effects of Age
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Effects of Injury
DETERMINANTS, TYPES, AND EFFECTS OF STRETCHING
INTERVENTIONS
 Alignment
 Stabilization:
 Intensity of stretch
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