Chapter 8: Regaining Stability

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14 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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Chapter 8: Regaining Stability
and Balance


Factors that impact balance


Muscular weakness


Proprioceptive deficits


ROM deficits


Balance is critical in dictating movement
strategies within the closed kinetic chain


Balance is a highly integrated dynamic process


Postural equilibrium is a broader term that
incorporates alignment of joint segments


Maintaining CoG within the limits of stability (LOS)


Vital component in rehabilitation


Joint position sense, proprioception and kinesthesia

Postural Control System


Components


Sensory detection of body motions


Integration of sensorimotor information within the
CNS


Execution of musculoskeletal responses



Balance is a static and dynamic process


Disrupted balance occurs due to two factors


Position of CoG relative to base of support is not
accurately sensed


Automatic movements required to maintain the CoG
are not timely or effective


Body position in relation
to gravity is sensed by


Visual


Vestibular


Somatosensory inputs


Balance movements
involve a number of joints


Ankle


Knee


Hip


Coordinated movement
along kinetic chain

Control of Balance


Tall body vs. Small base of support


Balance relies on network of neural connections


Postural control relies on feedback


CNS involvement


Sensory organization


Determines timing, direction and amplitude of correction
based on input


System relies on one sense at a time for orientation


For adults the somatosensory system is relied on primarily


Muscle coordination


Collection of processes that determine temporal sequencing
and distribution of contractile activity


Balance deficiencies


Inappropriate interaction among 3 sensory inputs


Patient that is dependent on one system may be presented
with inter
-
sensory conflict


Sensory Input


Somatosensory


Provides information concerning relative position of body
parts to support surface and each other


Vision


Measures orientation of eyes and head in relation to
surrounding objects


Role in maintenance of balance


Vestibular


Provides information dealing with gravitational, linear and
angular accelerations of the head with respect to inertial
space


Minor role when visual and somatosensory systems are
operating correctly

Somatosensation as it Relates to
Balance


Global term used to describe proprioception


Specialized variation of the sensory modality of
touch, encompassing joint sense (kinesthesia)
and position


Process


Input is received from mechanoreceptors


Stretch reflex triggers activation of muscles about a
joint due to perturbation


Results in muscle response to compensate for imbalance
and postural sway


Muscle spindles sense stretch in agonist, relay
information afferently to spinal cord


Information is sent back to fire muscle to maintain
postural control

Balance as it Relates to the Closed
Kinetic Chain


Balance


Process of maintaining body’s CoG within base of
support


Body’s CoG rests slightly above the pelvis


Kinetic chain


Each moving segment transmits forces to every other
segment


Maintaining equilibrium involves the closed kinetic
chain (foot = distal segment


fixed beneath base of
support)


Automatic postural movements


Determined via indirect forces created by muscles on
neighboring joints


Inertial interaction forces among body segments


Series of strategies are involved to coordinate
movement (joint strategies)


Injury to joints or corresponding muscles can result in loss of
appropriate feedback


Balance Disruption


In the event of contact body must be able to
determine what strategy to utilize in order to
control CoG


Joint mechanoreceptors initiate automatic postural
response


Selection of Movement Strategy


Joints involved allow for a wide variety of postures
that can be assumed in order to maintain CoG


Forces exerted by pairs of opposing muscles at a joint to
resist rotation (joint stiffness)


Resting position and joint stiffness are altered independently
due to changes in muscle activation


Myotatic reflex is earliest mechanism for activating muscles
due to externally imposed joint rotation


Ankle Strategy


Shifts CoG by maintaining feet and rotating body at a
rigid mass about the ankle joints


Gastrocnemius or tibialis anterior are responsible for torque
production about ankle


Anterior/posterior sway is counteracted by gastrocnemius
and tibialis anterior, respectively


Effective for slow CoG movements when base of
support is firm and within LOS


Also effective when CoG is offset from center


Hip Strategy


Relied upon more heavily when somatosensory loss
occurs and forward/backward perturbations are
imposed or support surface lengths are altered


Aids in control of motion through initiation of large and
rapid motions at the hip with anti
-
phase rotation of
ankle


Effective when CoG is near LOS perimeter and when
LOS boundaries are contracted by narrower base of
support


Stepping Strategy


Utilized when CoG is displaced beyond LOS


Step or stumble is utilized to prevent a fall


Instance of musculoskeletal abnormality


Damaged tissue result in reduced joint ROM causing
a decrease in the LOS and placing individual at a
greater risk for fall


Research indicates that sensory proprioceptive
function is affected when athletes are injured

Assessment of Balance


Subjective Assessment


Traditionally assessed via the Romberg Test


Feet together, arms at side, eyes closed


Loss of proprioception is indicated by a fall to one side


Lacks sensitivity and objectivity, qualitative assessment


Balance Error Scoring System (BESS)


Utilizes three stances


Double, single, tandem on both firm and foam surfaces


Athletes are instructed to remain motionless with
hands on hips for 20 seconds


Unnecessary movements and correction of body
position are counted as ‘errors’ (max score = 10)


Results are best utilized if compared to baseline data


Semi
-
dynamic and dynamic tests


functional reach tests


timed agility tests


carioca


hop test


Bass test for dynamic balance


Timed T
-
band kicks


Timed balance beam walks (eyes open and closed)


While criticized for merely reporting time of posture
maintenance, angular displacement or distance covered


test can provide valuable information about function and
return to play capability

Objective Assessment


Balance systems


Provide for quantitative assessment and training
static and dynamic balance


Easy, practical and cost
-
effective


Utilize to assess:


Possible abnormalities due to injury


Isolate various systems that are affected


Develop recovery curves based on quantitative measures in
order to determine readiness to return


Train injured athlete


Computer interfaced force
-
plate technology


Vertical position of CoG is calculated


Vertical position of
CoG movement =
indirect measure of
postural sway


Multiple manufacturers


Frequent consultation
may be required with
manufacture to
decipher conflicting
terminology between
manufacturers


Force plate measures


Steadiness, symmetry,
dynamic stability


Steadiness


Ability to keep body as motionless as possible


Measure of postural sway


Symmetry


Ability to distribute weight evenly between 2 feet in upright
stance


Measures center of pressure, center of balance and center of
force


Dynamic stability


Ability to transfer vertical projection of CoG around a
stationary supporting base


Perception of safe limit of stability


Utilization of external perturbation


Some are systematic (sinusoidal) while others are
unpredictable and determined via changes in subject sway



Center of Pressure (CoP)


Center of the distribution of the total force applied to the
supporting surface


Calculated from horizontal moment and vertical force data
through a triaxial force platform


Center of Balance (CoB)


Point between feet where the ball and heel of each foot has
25% of the body weight (Chattecx Balance System)


Relative weight positioning


Center of Vertical Force (CoF)


Center of vertical force exerted by the feet against the
support surface (Neurocom’s Equitest)


Total force applied to the platform fluctuates due to
body weight and inertial effects of body movement


Forces based on motion of CoG


Athlete should maintain their CoP near A
-
P and M
-
L
midlines


Additional Balance Parameters


Postural sway


Deviation from CoP, CoB, or CoF


Determined using mean displacement, length of sway path,
length of sway area, amplitude, frequency and direction
relative to CoP


Equilibrium Scores


Sway index (SI)


Scatter of data about CoB (Chattecx)


Forceplate technology


Fully integrated hardware/software


Allowing for static and dynamic postural assessment


Single or double leg stance, eyes opened or closed


Moving visual surround for sensory isolation and
interaction


Long force plate, dynamic multi
-
axial equipment

Injury and Balance


Stretched/damaged ligaments fail to provide
adequate neural feedback, contributing to
decreased proprioception and balance


May result in excessive joint loading


Could interfere with transmission of afferent impulses


Alters afferent neural code conveyed to CNS


Decreased reflex excitation


Caused via a decrease in proprioceptive CNS input


May be the result of increased activation of inhibitory
interneurons within the spinal cord


All of these factors may lead to progressive
degeneration of joint and continued deficits in
joint dynamics, balance and coordination


Ankles


Joint receptors believed to be damaged during injury
to lateral ligaments


Less tensile strength when compared to ligament fibers


Results in deafferentation and diminished signaling via
afferent pathways


Articular deafferentation


reason behind balance training in
rehabilitation


Orthotic and bracing intervention


Enhancement of joint mechanoreceptors to detect
perturbations and provide structural support for detecting and
controlling sway


Chronic ankle instability


Recovery of proprioceptive capabilities


Modifications in movement strategies to enhance
proprioceptive input



Increased postural sway and/or balance instability
may not be due to a single factor


May be related to both neurological and
biomechanical factors at the ankle joint


Altered biomechanical alignment


alters somatosensory
transmission


Deficit in kinetic chain due to instability vs.
deafferentation



Knee Injuries


Ligamentous injury has been shown to alter joint
position detection


ACL deficient subjects with functional instability exhibit this
deficit which persist to some degree after reconstruction


May also impact ability to balance on ACL deficient leg


Mixed results have been presented with static testing


Isometric muscle strength could compensate for
somatosensory deficits


Definition of functionally unstable may vary


Role of joint mechanoreceptors with respect to end range
and the far reaches of the LOS


More dynamic testing may incorporate additional
mechanoreceptor input


results may be more
definitive



Head Injury


Balance has been utilized at a criterion variable


Additional testing is necessary in addition to balance
and sensory modalities


Postural stability deficits


Deficits may last up to three days post
-
injury


Result of sensory interaction problem
-

visual system not
used effectively


Objective balance scores can be utilized to determine
recovery curves for making return to play decisions

Balance Training


Vital for successful return to competition from
lower leg injury


Possibility of compensatory weight shifts and gait
changes resulting in balance deficits


While advanced technology is an amenity,
imagination and creativity are often the best
tools when there are limited resources


Functional rehabilitation should occur in the
closed kinetic chain


nature of sport


Adequate and safe function in the open chain is
critical = first step in rehabilitation


Rules of Balance Training


Exercise must be safe and challenging


Stress multiple planes of motion


Incorporate a multisensory approach


Begin with static, bilateral and stable surfaces and
progress to dynamic, unilateral and unstable surfaces


Progress towards sports specific exercises



Utilize open areas


Assistive devices should be in arms reach early
on


Sets and repetitions


2
-
3 sets, 15


30 repetitions or 10 of the exercise for
15 sec.


30 seconds later on in program


Classification of Balance Exercises


Static


CoG is maintained over a fixed base of support, on a stable surface


Semi
-
dynamic


Person maintains CoG over a fixed base of support while on a
moving surface


Person transfers CoG over a fixed base of support to selected ranges
and or directions within the LOS, while on a stable surface


Dynamic


Maintenance of CoG within LOS over a moving base of support while
on a stable surface (involve stepping strategy


Functional


Same as dynamic with inclusion of sports specific task


Phase I


Non
-
ballistic types of drills


Static balance training


Bilateral to unilateral on
both involved and
uninvolved sides


Utilize multiple surfaces to
safely challenge athlete
and maintaining motivation


With and without
arms/counterbalance


Eyes open and closed


Alterations in various
sensory information


ATC can add perturbations


Incorporation of multiaxial
devices


Train reflex stabilization
and postural orientation




Phase II


Transition from static to dynamic


Running, jumping and cutting


activities that require
the athlete to repetitively lose and gain balance in
order to perform activity


Incorporate when sufficient healing has occurred


Semi
-
dynamic exercised should be introduced in the
transition


Involve displacement or perturbation of CoG


Bilateral, unilateral stances or weight transfers involved


Sit
-
stand exercises, focus on postural

Bilateral Stance Exercises


Unilateral Semi
-
dynamic exercises


Emphasize
controlled hip flexion,
smooth controlled
motion


Single leg squats,
step ups (sagittal or
transverse plane)


Step
-
Up
-
And
-
Over
activities


Introduction to
Theraband kicks


Balance Beam


Balance Shoes


Phase III


Dynamic and functional types of exercise


Slow to fast, low to high force, controlled to
uncontrolled


Dependent on sport athlete is involved in


Start with bilateral jumping drills


straight plane
jumping patterns


Advance to diagonal jumping patterns


Increase length and sequences of patterns


Progress to unilateral drills


Pain and fatigue should not be much of a factor


Can also add a vertical component to the drills


Addition of implements


Tubing, foam roll,


Final step = functional activity with subconscious
dynamic control/balance

Phase III Exercises

Clinical Value of High
-
Tech
Training and Assessment


Balance systems allow
for deficit detection and
quantitative assessment


Utilize both in the
clinical setting and
research setting


Multiple tests and
variables can be
assessed and monitored
with respect to
performance