Regaining Postural Stability Balance Chapter 7 Factors that

Regaining Postural Stability & Balance Chapter 7

• 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 Co. G 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 Co. G relative to base of support is not accurately sensed – Automatic movements required to maintain the Co. G 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 Co. G within base of support – Body’s Co. G 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 Co. G – 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 Co. G • 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 Co. G 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 Co. G movements when base of support is firm and within LOS – Also effective when Co. G 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 Co. G is near LOS perimeter and when LOS boundaries are contracted by narrower base of support

• Stepping Strategy – Utilized when Co. G 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 Co. G is calculated

– Vertical position of Co. G 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 Co. G 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 (Co. P) • 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 (Co. B) • 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 (Co. F) • 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 Co. G – Athlete should maintain their Co. P near A-P and M-L midlines

• Additional Balance Parameters – Postural sway • Deviation from Co. P, Co. B, or Co. F • Determined using mean displacement, length of sway path, length of sway area, amplitude, frequency and direction relative to Co. P – Equilibrium Scores – Sway index (SI) • Scatter of data about Co. B (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 – Co. G is maintained over a fixed base of support, on a stable surface • Semi-dynamic – Person maintains Co. G over a fixed base of support while on a moving surface – Person transfers Co. G over a fixed base of support to selected ranges and or directions within the LOS, while on a stable surface • Dynamic – Maintenance of Co. G 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 Co. G • Bilateral, unilateral stances or weight transfers involved • Sit-stand exercises, focus on postural

Bilateral Stance Exercises

– Unilateral Semidynamic 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