Flexibility & Stability KPE160 Module 04 PDF

Flexibility & Stability Range-of-Motion Laxity KPE160 Module 04 Flexibility Outline Range-of-Motion Joint Play / Laxity Flexibility / Sufficiency Outline Equilibrium and Stability Health and Performance correlates of flexibility,...

Flexibility & Stability Range-of-Motion Laxity KPE160 Module 04 Flexibility Outline Range-of-Motion Joint Play / Laxity Flexibility / Sufficiency Outline Equilibrium and Stability Health and Performance correlates of flexibility, laxity & stability Exercises for desirable Flexibility Exercises for desirable Stability Range-of-Motion How much joints move in ways they should Range-of-Motion (RoM) The extent of joint movement in each physiologic DoF of motion is the “range-of-motion” in that DoF > normal RoM = “flexible” or “hypermobile” A hypermobile elbow (hyperextends > 10 degrees) < normal RoM = “hypomobile” or “restricted” scifighting.com Specifying Range-of-Motion (RoM) Clinicians often use semi-quantitative (ordinal / categorical) scales, e.g.: very restricted < slightly restricted < normal < slightly hypermobile < very hypermobile Quantitative description preferred; for each DoF we can specify one number - total RoM for that DoF, +/or two numbers - end points of RoM in each direction e.g. – elbow flex-ext = 160° from -5° to 155° flexion Active vs. Passive RoM Passive (PRoM) = RoM under external loading (gravity, contact & reaction forces) PRoM of ankle dorsiflexion Active (ARoM) = RoM under internal (muscular) loading (and potentially gravity depending on body position) ARoM of ankle dorsiflexion Load-Movement Curve for RoM neutral zone motion = “easy” or facile motion; boundary = inflection in slope active RoM - typically within neutral zone passive RoM - typically slightly beyond past neutral zone; always ≥ ARoM Load (N-m) Active RoM Neutral Zone Passive RoM - + Movement (degrees) Assessing Passive Range-of-Motion Clinicians use visual observation ± goniometry Note paradigm of loading (position / orientation in gravity, methods of loading) Ask subject to relax, let their body go with gravity, make no effort to resist Move target joint until significant stiffening (↑ load required for further movement) felt, OR subject reaches their tolerance Measure target joint angle at ends of RoM Ask subject “where they feel it” Note any discomfort / crepitation PRoM of ankle dorsiflexion RoM of Multi-DoF Joints Position in one DoF can affect RoM in other DoFs; examples: GHJ elevation is altered by position in humeral rotation Hip elevation is altered by position in both HAb-Ad and femoral rotation Very difficult to fully describe multi-DoF RoM well! Several ways to depict multi-DoF RoM, some better than others generally done poorly Ways to Describe RoM of Multi-DoF Joints RoM in one DoF with other DoFs held in neutral position (limited) Concurrent RoM in multiple DoFs in one of several ways (better) use a particular subset of combined movements assess circumference of 2 DoFs with third held in fixed position  Flex 270 Mollweide Projection of Multi-DoF RoM 210 180 150 120 90 Mollweide Ab 180 90 30 -30 -90 -180 Ad projection 60 Surface of spherical globe is cut, 30 stretched and flattened 0 -30 -60 -90 Ext  Flex 270 Concurrent RoM of 2 DoFs 210 180 150 Assess limits of two DoFs concurrently; e.g. – hip F-E and Ab-Ad 120 90 Specify position of 3rd DoF if applicable; Ab 180 90 30 -30 -90 -180 Ad e.g. – hip IR-ER; do it 3 times: 60 hip in neutral IR-ER 30 hip in max IR 0 hip in max ER -30 -60 -90 Ext RoM in Multi-Articular Chains If joint movement in a particular DoF of motion can be constrained by tension in a multi-articular structure, (often the case) then the RoM of that joint in that DoF may be altered by the position of other joints in the chain Examples? Need to measure RoM in target joint multiple times, with other joints at end-of-range in each direction Laxity How much joints move in ways they should not Joint Play / Laxity The extent of a joint movement in a non-physiologic DoF of motion is the “joint play” or “laxity” in that DoF > normal joint play = “laxity” < normal joint play = “restriction” Lachman test for anterior translational laxity of knee Assessing Joint Laxity Clinicians use their hands to cause NP motion; they assess two things: “Joint Play”: extent of “easy” movement in a non-physiologic DoF 1+, 2+, 3+ / minimal, moderate, substantial / etc. “End Point Feel”: how quickly the joint stiffens in a non-physiologic DoF hard, soft, mushy, rubbery, firm, etc.... Anterior drawer test of ankle Flexibility Definitions and Measures Definitions of Flexibility The various definitions of flexibility may apply to individual joints, links, chains of joints, or a whole person Several different definitions: statistical flexibility adequate task flexibility passive sufficiency of multi-articular links generalized hypermobility / laxity “Statistical” Flexibility A joint is flexible in one DoF (or a direction of that DoF) if it displays > average RoM μ = 135° in that DoF (or direction) 100 110 120 130 140 150 160 170 A whole joint, chain or person Normative distribution of PROM knee flexion is said to be flexible if “most” of its DoFs / joints are flexible “Adequate” Task Flexibility ARoM sufficient to perform a target task Different for different tasks / sports Examples: dancers, gymnasts, divers, figure skaters – need overall / all-joints flexibility runners vs. cyclists – hip flexors and hamstrings Reliever John Gant winds up in 2016 deadspin.com throwers – need abnormal extent of shoulder ER to wind up Multi-Articular Links Span more than one skeletal articulation Most common tensile constraints of motion Examples: Muscles – span 1 to 80+ articulations Ligaments – span 0 to 2 (+?) articulations Fascia – connected across entire body Nerves and Vessels – head to toes! Latissimus dorsi spans over 80 articulations! TeachPE.com Passive Sufficiency of Links Sufficient length of links such that they do not constrain passive motion of any joints they span Term typically only applied to multi-articular links Do uni-articular links often constrain motion? Ligaments? Yes!! They limit laxity and some DoFs of RoM in some joints Muscles? Not very often!! Uni-articular muscles typically passively sufficient Tests of Passive Sufficiency of Bi-Articular Muscle For a bi-articular muscle, compare the PRoM of one (either) articulation spanned by the muscle (the “target PRoM”) in two situations: joint at other end pre-positioned to relax the muscle joint at other end pre-positioned to tighten the muscle If target joint PRoM is equal in both situations, then that muscle is passively sufficient in length If target joint PRoM is less when other joint positioned to tense the muscle, then that muscle is passively insufficient in length Example: Bi-Articular Hamstrings When bi-articular hamstrings are stretched, they potentially constrain concurrent hip flexion and knee extension if passively sufficient, they constrain neither Tests for passive sufficiency: measure knee extension with hip flexed vs. extended measure hip flexion with knee flexed vs. extended One way to stretch bi-articular hamstrings popsugar.com  Passive Sufficiency of Bi-Articular Hamstrings Version 1 – measure knee extension with hip flexed vs. hip extended KE with HE 1. With hip extended: hamstrings pre-relaxed by extending hip first passively KE with HF passively KE with HF 2. With hip flexed: sufficient = KE with HE insufficient < KE with HE hamstrings hamstrings hamstrings hamstrings pre-tensioned pre-tensioned by flexing by flexing hip first hip first  Passive Sufficiency of Bi-Articular Hamstrings Version 2 – measure hip flexion with knee flexed vs. knee extended 1. With knee flexed 2. With knee extended (pre-positioned to tense BA hams) (pre-positioned to relax BA hams) HF with KF passively sufficient since passively insufficient since HF with KE = HF with KF HF with KE < HF with KF Multi-Articular Passive Sufficiency Structures that cross more than 2 joints are passively sufficient if they do not constrain RoM of any joint that they cross Examples of such multi-articular structures include nerves, blood vessels, fascia and some muscles To assess this, you need to consider the positions of 3 or more joints Assessing Multi-Articular Passive Sufficiency Select one joint as the target for measurement of RoM in a direction that stretches the multi-articular structure being assessed Measure the target RoM twice: once with both control joints in positions that stretch the multi-articular structure being assessed once with both control joints in positions that relax the multi-articular structure being assessed If target RoM changes, the structure is not passively sufficient Example: the Sciatic Nerve Sciatic nerve runs down the posterior aspect of the lower extremity it is stretched by hip flexion, knee extension, and ankle dorsi-flexion* (* this is a bit of a simplification, adequate for our purposes) Using hip flexion as target RoM, measure hip flexion RoM twice: Once with knee extended and ankle dorsi-flexed (both stretch the nerve) Once with knee flexed and ankle plantar-flexed (both relax the nerve) If hip flexion RoM changes, the nerve is not passively sufficient You should be able to describe similar tests using either knee extension or ankle dorsi-flexion as target RoM… Flexibility and Laxity are Correlated Why? Genetics? variations in different types of collagen e.g. – Ehlers-Danlos Syndrome variations in other genes affecting muscle or skeletal joint anatomy? Environment? An individual with Ehlers-Danlos Syndrome people stretching in multiple / all DoFs? displays hypermobility and elasticity of skin en.wikipedia.org Beighton Score for Generalized Hypermobility / Laxity Beighton Score (out of 9) assesses Joint Hypermobility Syndrome (JHS) palms-to-floor with knees extended thumb-to-forearm x2 MCPJ5 DF ≥ 90 x2 elbow HE ≥ 10 x2 knee HE ≥ 10 x2 JHS correlated with generalized ligamentous laxity (GLL) Beighton score ≥ 7 ≡ JHS/GLL (5-6 considered borderline) Interpreting Beighton Score Grouped into 3 bands of results: 0-4 normal 5-6 mild JHS / GLL 7-9 JHS / GLL Equilibrium and Stability Balance and Buffer Equilibrium Origin ~1600; from Latin: aequilībrium, equiv. to aequi- (equal) + lībra (balance) hence “equal balance” Typical dictionary definition: a state of balance achieved by equal action of opposing forces In systems theory, a state in which a variable of interest tends toward a constant value Mechanical Equilibria Mechanical systems with zero net force / moment of force  constant momentum (Law of Inertia) Static mechanical equilibrium = positional equilibrium constant position, zero momentum Dynamic mechanical equilibria = momentum equilibrium changing position, constant momentum Equilibrium Sway Equilibria may tend toward a constant value, but vary around it In mechanical systems, especially for static equilibria, this may be referred to as sway about an equilibrium value Equilibrium sway be quantified in several ways: frequency of sway magnitude of sway other measures Stability of an Equilibrium Origin ~1300; from Latin: stabilis; equiv. to sta- (stāre to stand) + -bilis (able) hence “able to stand” Typical dictionary definitions are: fixed in position; firmly positioned (not useful for dynamic equilibria) resistant to / able to withstand change or perturbation (much better!) Stable equilibria withstand energetic perturbation: perturbation adds kinetic and/or potential energy potential energy stored during perturbation does work to return system to equilibrium How stable is an equilibrium? All equilibria are not equally stable! How much perturbation can be withstood? highly stable neutral unstable highly stable equilibrium equilibrium equilibrium unstable equilibrium equilibrium How deep is the “potential energy well”? Stability Buffer Stability buffer = amount of energy (J) required to destroy equilibrium In this example, the buffer is a gravitational potential energy well, the size of which depends on the height of the walls h2 h1 SB1 = SB2 = SB3 = 0 J m·g·h1 m·g·h2 A Clinical Kinesiological Perspective Kinesiologists are interested in the stability of two types of mechanical equilibria: Postural stability Joint stability Postural Stability Ability to withstand perturbations of a static body position without collapse Muscular activation (typically) required to balance the force of gravity and its moments http://www.anvari.org/db/fun/Photography/Balance.jpg Postural Stability Buffer Postural Stability Buffer ≡ work (energy) required to cause collapse Postural stability buffer determined by 2 variables (W = F ⋅ d) Base-of-Support  distance of CoP from margins of BoS (more in Module 5) Stiffness  force required to move CoP through that distance inertia of body mass, tissue elasticity & viscosity, active muscle moments Joint Stability Joint Stability ≡ stability of positional equilibria in NP DoFs Correlated with joint laxity but not 1:1 lax joints can be stable (not uncommon) – how? stay tuned… examples? http://www.anvari.org/db/fun/Photography/Balance.jpg Active vs. Passive Stabilization Muscle activation may (not) be required to maintain postural and / or joint equilibria – referred to as active stabilization Passive stabilization results from forces and moments that require no muscular activation: mass  gravity and inertia tissue elasticity and viscosity external (ground) and internal (joint) reaction forces Stabilization by Muscle Activation Some muscle activation is typically required for: postural stability in most positions (i.e. – unless lying down) joint stability (more so for more lax joints) Which muscle(s)? next slide… What pattern of activation? }  later today How to train muscle for this? General vs. Specific Active Stabilization General stabilization in multiple DoFs through co-activation of 2 or more agonist-antagonist muscle groups primary means of active stabilization – nearly every posture and movement force along shared axis of agonist-antagonist pairs compresses joint surfaces; increase stiffness of motion tangential to joint surfaces (shear motion) forces and moments in other DoFs cancel out – no acceleration Specific stabilization in one DoF by activation of one muscle acting alone individual muscles activated in situations in which they can stabilize one DoF Relations to Health and Performance Are flexibility, laxity, and/or stability desirable? How and why? For what goals? General Flexibility and Health? No evidence that I know of suggests that general flexibility is correlated with lower overall injury rates Some studies show general flexibility is correlated with higher rates of certain injuries e.g. – Beighton score >6 correlated with increased risk of joint dislocations Specific Flexibility and Health? Some studies show specific joint flexibility correlated with lower incidence of specific disorders e.g. – flexible ankle DF is correlated with fewer foot & ankle problems Some studies show specific joint restrictions are correlated with higher incidence of specific disorders e.g. – inflexible hip correlated with higher incidence of OA Flexibility & Performance? Flexibility improves performance capacity; three issues: adequate task flexibility – sufficient “reach” and “runway” to perform task muscle contractile velocity and power output* (longer muscles faster  more powerful) may optimize resting length “sweet spot” for a task* (force-length relationship) * these effects occur ONLY IF flexibility is generated by longer muscles! Task-specific examples: Thrower: RoM shoulder Runner: RoM hip + knee May be at odds with health concerns (but not necessarily so) Laxity, Health, and Performance Joint laxity is generally correlated with rates of joint injury Joint laxity is not required for performance since the joint is moving in an undesirable way (unless you have a circus job dislocating your joints for the amusement of spectators) Joint laxity is not a good thing Stability and Health Postural Stability prevents slips & falls Joint Stability reduces risks of joint injuries & disorders Stability and Performance Postural Stability many examples of how it helps improve performance! how many can you think of ? Joint Stability no obvious performance benefits other than avoiding DL What is Desirable Flexibility & Stability? Depends on your goals health? performance? doing what activities? Exercise for Flexibility Stretching the Truth? Desirable Flexibility Task-specific adequate flexibility for: Activities of daily living (ADLs) Occupational activities Sport & Recreation activities alamy.com bicmagazine.com reuters.com Consider health and performance relations of flexibility in relation to the tasks you wish to be capable of doing well Can You Improve Flexibility? It depends on the constraint(s) of motion If impingement (compression of an articulation) is constraining motion, cannot improve flexibility; attempting to do may cause damage If it is tension in a link (stretching that link) is constraining motion, then you may be able to improve flexibility by: lengthening that link and/or improving its mobility relative to surroundings increasing perceptual tolerance of tension in the constraining tensile What is “Stretching”? lengthening of tensile links in a mechanical system EVERY human movement involves stretching of muscle and passive tissues! medium.com Common Patterns of “Stretching Exercise” We acknowledge that we are stretching when perform movements with a primary goal of lengthening target structures Multiple mechanisms of stretching with non-mutually-exclusive labels (lending confusion): “static”, “dynamic”, “ballistic”, “active”, “passive”, “hold-relax”, “PNF”, etc. Variables in a Single “Stretching” Movement What constraint(s) of motion is(are) being stretched (lengthened)? What is the force vs. length vs. time profile of the stretch? How intense is the stretch (how much force is causing it)? How much is it lengthened (how close to end-range / failure)? Is it moving (static vs. dynamic stretching)? How quickly? For what duration is it held at end-range? How is the stretching force generated? “actively” by antagonist muscles vs. “passively” by external forces How is the stretching force resisted? actively by agonist muscle activation vs. passively (visco-elastic lengthening)  Range Intensity Velocity Duration Stretch Stretch “Type” (extent of (magnitude of (rate of (time held at Generator(s) Resistor(s) lengthening) stretching force) lengthening) end range) Variable, External Zero, typically Variable, Static stretch End PRoM typically (passive) or Passive reached slowly typically 5-60s unspecified internal (active) Variable, Non-zero, Typically Passive & Dynamic stretch End A/PRoM typically variable slow- Transient internal (active) Active unspecified moderate Typically higher Non-zero, Typically Passive & Ballistic stretch End A/PRoM Fleeting at end-range typically higher internal (active) Active Variable, Resist-Relax / Zero, typically Variable, Combined and Passive & End PRoM typically PNF reached slowly typically 5-10s opposite Active unspecified Mechanical & Perceptual Effects of Stretching? Short-Term Stretching (i.e. - one or a few sessions of stretching) short-term mechanical effects (length, stiffness, etc.) short-term perceptual effects (tolerance of tension in constraints of motion) no long term effects Long-Term Stretching (i.e. - regular / frequent stretching over a prolonged time period) long-term perceptual effects (tolerance of tension in constraints of motion) potential mobilization (or lengthening?) of passive multi-articular links (e.g. nerves)? potential (unlikely) lengthening of muscle (sarcomeres added in series) with “normal” stretching Short-Term Mechanical Effect - Lengthening Visco-elastic stretching of sarcomeres / elastic elements  temporary lengthening (τ1/2 ~ 10min)  returns to resting state at similar rate when unloaded When maximally stretched for prolonged periods, sarcomeres are pulled apart Transient increase in lumbar flexion RoM (i.e. lengthened > 3µm) with 20-minute static stretch MicGill & Brown (1992) Short-Term Perceptual Effect - Tolerance Tolerance of stretching increases with repetition in short-term Experimental Leg Stretched hamstrings  closer to tissue failure (!) (is this a good thing?) No change in resting length or stiffness after visco-elastic recovery Control Leg Unstretched hamstrings [e.g. Halberstma et al APMR 1994, Magnusson et al JP 1996] Magnusson et al JP 1886 Long-Term Stretching and RoM Many studies (mostly poor quality) show increased RoM as a result of chronic stretching (various regimens ~equally effective?) most relate to ankle DF RoM or hamstring sufficiency Almost none examine or control for whether observed increase in flexibility is mediated by perceptual tolerance vs. structural changes (changes in muscle) Muscle Lengthening or Perceptual Tolerance? Whether observed increases in RoM with chronic stretching are due to changes in muscle properties (length, stiffness, CSA, etc.) or perceptual tolerance of tension in stretching is unknown Studies since mid-1990s favour perceptual tolerance as mechanism Limitations < 8 weeks, ? variables Limb Growth and Stretching in Children We believe that bone growth leads limb length growth and other tissues follow: muscles, nerves, vessels may grow longer because the newly-longer bone has placed them under tension 24/7 this possibly explains “growing pains” – discomfort of constant stretching of muscles, nerves, vessels and fascia Lack of research on stretching exercises in healthy children examining whether / how stretching affects muscle-length growth anecdotal evidence / widespread belief that regular stretching in children leads to rapid and longer-lasting gains in flexibility than stretching in adults. Is this the best (only?) opportunity to grow long multi-articular muscles? Can muscles grow longer in adults? Limb-Lengthening Surgery Gavriil Ilizarov (1921-1992) developed methods for lengthening and straightening the limbs of people with deformities or dwarfism Distraction osteogenesis sever a bone into two fragments attach each fragment to fixation devices use apparatus to gradually separate the fixators Tissues grow longer at different rates bone > muscle > fascia, vessel > nerve Maximum tolerable rate ~1mm/day determined by nerve [Paley personal communication] Optimal Regimen of Static Stretching? While there is a significant body of evidence that frequent / prolonged static stretching can increase muscle length, the optimal regimen of variables (range, intensity, volume, etc.) is unclear; for example: Apostopoulos et al FP 2015 – “no conclusions possible” about intensity vs. range of stretching Thomas et al IJSM 2018 – total weekly frequency and/or volume seems more important than time per session Lengthening (Eccentric) Activation Some studies have shown muscle fascicle lengthening after significant “eccentric” exercise Optimal regimen of variables (range, intensity, volume, etc.) unclear Bourne et al BJSM 2017 Exercise for Stability It’s all about Muscle Co-Activation! Basic Stabilization Exercise Isometric Co-Activation hold a posture still – do not move – static equilibrium Neutral Postures (~mid-range of each joint) not generally a good idea to maintain joints at end-range position (stress placed on passive constraints of motion like ligaments and articulations) “Strength Endurance” exercise i.e. – prolonged muscle activations to fatigue Example: McGill’s “Basic Three” Semi-Remedial Side Bridge Partial Curl Up Bird Dog Normal Side Bridge acefitness.org Advancement of Stabilization Exercise Principles for challenging stability of equilibria: Unstable Platforms Perturbations Heavy Breathing Stabilizing during Movement / End-range Joint Stability Unstable Platforms Two different types Rigid platforms with reduced base-of-support (reduces the work required to move CoG outside BoS  fall) Inflatable platforms with reduced rigidity (complex mechanics, more difficult to maintain equilibrium) Can reduce stability in 1 or more DoF Perturbations of Equilibrium Challenges stability buffer by adding (potential or kinetic) energy Internal perturbation – segmental motion, altered muscle forces External perturbation external loads – contact and reaction with inertia, elasticity or viscosity Heavy Breathing Breathing maximally requires diaphragmatic contraction lengthens abdominal muscles (if they relax); or increases intra-abdominal pressure (if they don’t); or both If abdominal wall muscles relax to allow heavy breathing, this destabilizes the trunk We (especially athletes) need to be stable during activity > at rest! Train for truncal stability during heavy breathing! Stability During Movement Consider joint stability during movement need to prevent motion in NP DoF throughout the RoM of physiologic DoF Exercises that focus on this are an important part of advanced stability programs Maintaining adequate co-activation throughout RoM is not easy, and comes with some costs! stiffness in NP DoFs is desired, but stiffness in P DoFs? Necessary for healthy high performance Costs of Active Stabilization Stiffness in physiologic DoFs increased metabolic work required to move slower movement, possibly altered coordination Compression of joints – does it cause damage? hyaline cartilage in synovial joints? inter-vertebral discs? Constraint of breathing unless trained Summary and So What? What you should have learned in this module Why it matters Summary Range-of-Motion – how much joints move in ways they should Laxity – how much joints move in ways they should not Flexibility – statistical, task-specific adequacy, passive sufficiency Summary Equilibrium and Stability Health and Performance correlates of flexibility, laxity & stability Exercises for desirable Flexibility Exercises for desirable Stability So What? You need to be able to accurately describe range-of-motion if you choose a career in clinical kinesiology / MSK health care Adequate motion capacity is critical for performance and some aspects of health (e.g. - independent living capacity) Not all types of mobility are desirable! (e.g. - joint laxity is generally a bad thing) You need to understand the difference in order to understand what types of exercise are good for your health or performance capacity – our subject in the next class So What? Many myths about stretching and flexibility abound – as a kinesiologist, you need to bust them Desirable flexibility and stability are related to health and performance goals flexibility is mostly related to performance capacity, some health issues stability is mostly related to health (injuries), some performance issues Knowing what types of exercise generate desirable motion capacity is critical for engaging in and prescribing appropriate exercise How to achieve desirable motion capacity