EXSS 2020 cheat sheet - Summary Biomechanics PDF

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Which movements occur in the sagittal plan? = Flexion, extension, hyperextension, dorsiflexion, plantarflexion. What movements occur in the frontal plan? =abduction, adduction, lateral flexion, radial/ulnar deviation, inversion, eversion, scapula elevation and depression. What movements occur in the frontal plane?= medial/lateral rotation, pronation, supination, horizontal abduction and adduction. The greater the radius of rotation (r), the greater the linear distance (s) travelled by a point on a rotating body. Components of total drag force: WAVE DRAG, SURFACE DRAG & FORM DRAG. Form drag= Pressure differential between lead & rear sides of a body moving thru fluid Results from suction like F created between positive (+ve) & negative (-ve) pressure zones when turbulence is present. Longer leading edge Fluid particles separate earlier & strike the object’s surface at a > angle of incidence (angle relative to object surface). Thus, minimises the ability of the fluid to exert a F on the object & lower drag Form Drag Some buses, train & trucks have flat front end Traps air molecules to allow accumulation of air at front of vehicle thus divergence from laminar flow earlier to lower drag (solid line) > drag when air diverts near front (dashed line). Adding tail to an object promotes landing flow as separation occurs later. E.g. of form drag is golf ball dimples. No dimples =no backspin = no lift. How the dimpling works (A) Turbulent zone behind ball Mass of air forces oncoming air molecules to separate from laminar flow earlier (B) Speed increase the effect more prominent i.e. greater drag (C) Very fast speeds, lower pressure associated with the turbulence allows oncoming air to ‘stick’ to ball or pass close to air & separation of this air occurs later Dimples on ball allow turbulent layer to form. WAVE DRAG: greater speed leads to greater wave length & height.

Wave drag doesn’t  constantly Active drag in swimming always lower. Active drag in swimming always lower or equal to drag in passive conditions. Thus suggesting technique strongly influences wave drag = skilled smaller waves. It’s by greater effective body length by stretching arm in front of body will reduce wave drag and lead to an earlier divergence of oncoming flow thus lowering pressure on the front of the head and thus minimising wave drag to then lower the turbulence and energy loss. Ways to minimise frontal drag 1. Wetsuits; little effect on upper body but substantial on lower limb it increases buoyant F (see wetsuit slide) 2. Move COM forward closer to the centre of buoyancy 46 Move lead arm outstretch for longer Move COM forw & lower torque creating the pitch Plus minimise wave & form drag. Why is the relationship between movements of joints of lower limb critical? Deviations coordination of patterns. Energy cost of walking may increase. Shock absorption at impact & propulsion may not be as effective. Gait pathology. GAIT : Role of the Ankle Joint: Stance phase- Movement of foot to tibia (sagittal) important -Allows shock absorption at heel strike & during stance phase Vital ‘push off’ or propulsive stage immediately before toe leaves ground. Swing phase: Ankle joint allows foot clearance- Lacking some pathological gait patterns. STANCE: Loading response IC in neutral position, & TA active swing & early stance & prepare control movement into PF. Then PF 3-5°until foot flat PF eccentrically TA Coupled = pronation & internal tibia rot (subtalar joint). STANCE: Midstance ∆ ankle jt ϴ: foot segment stationary, tibia segment moving TA stops & triceps surae starts eccentrically. Begins DF DF max 10° as tibia moves over ankle joint TA stops & triceps surae starts eccentrically - Plantarflex. STANCE: Terminal Stance Propulsive phase At begin of double support Peak DF and thus rapid ankle PF Triceps surae maintain ankle angle as knee starts to flex - Tibia more external rotated & foot supinated - Toes remain flat with extension at metatarsophalangeal joints - Hindfoot inversion. STANCE: Pre-Swing OI PF concentrically triceps surae Extension toes MTP joints and thus tightening of plantar fascia. Lock midtarsal joint Maximum supination, hindfoot inversion, external tibial rotation. Stability Toeoff peak PF. SWING: Initial Swing PF peak Rapidly DF allow foot clearance from ground T. SWING: Mid Swing Neutral position reached by mid swing until next heel strike TA. SWING: Terminal Swing TA hold ankle position & greater intensity for loading response. Role of the Knee Joint: STANCE: Loading Response Extension Hamstrings end swing & act braking mechanism Flex to ~20° when knee under max wt-bearing load Flexes Quads eccentrically to limit speed & magnitude of flexion Occurs same time PF with net effect of acting as shock absorber during loading of lower limb. STANCE: Midstance Quad eccentric to

control rate of knee flexion 1st peak of flexion Knee extends initially through concentric quadriceps. STANCE: Terminal Stance Peak of extension PF/knee extension couple Active PF moves GRF forward into forefoot & in front of knee joint Attempts extension knee Important pathological gait Gastrocnemius knee flexes, prevent hyperextension & initiate flexion. STANCE: Terminal Stance Propulsive phase as 2nd knee flex start as heel lifts Undergoes rapid flexion in preparation for swing End: force vector behind knee, aids flexion RF eccentric to prevent flex occur too rapid. STANCE: Pre-swing ~40° Knee flexes due double pendulum 1° hip flexion. Shank left behind due to its inertia thus knee flexion RF eccentric prevent excessive knee flexion. STANCE: Initial- to midswing Knee flexion primarily due to hip flexion .: pendulum no muscle contraction Allows toe clearance During initial-mid swing knee continues to flex to max 65-70° < fast gait due cocontraction RF & hamstrings. STANCE: Terminal Swing Rapid extension to prepare for 2nd heel strike Extension mainly (shank) passive double pendulum Eccentric hamstrings prevents abrupt hyperextension.

Role of the Hip Joint: STANCE: Loading response Max hip flexion at mid swing maintained until IC thus hip extends Hamstrings active late swing & gluteus maximus starts IC thus start concentric hip extension. STANCE: Mid-stance Hip extends as body moves over limb Hip extension Concentric gluteus maximus & hamstrings stops as hip extension via inertia & gravity Hip abduction (gluteus medius & TFL) maintain pelvis Opposite foot leaves ground, pelvis only supported by stance hip. STANCE: Terminal-stance Max hip extension just after opposite foot IC Hip abduction stabilise pelvis, then stops prior IC other foot. STANCE: Pre-Swing Extension to flex. Primarily flexion from adductor longus; Hip flexion due gravity & tension hip ligaments, & RF & adductor longus. SWING: Initial to mid-swing Weight transfer forward limb Trailing limb begins flex Pre-swing period toe leaves ground & hip flexes rapidly & reaches maximum flexion just before heel strike Flexes iliopsoas, aided by gravity. SWING: Terminal-swing; Hip flexion stops. Often small movement towards extension. Due foot placement or prepositioning just prior to heel strike. Hamstring limit rate knee extension, while maintain hip flexion position. Muscle Biomechanics: Behavioural Properties of the Musculotendinous Unit- Extensibility(Ability to be stretched or to greater in length), Elasticity(Ability to return to norm resting length following stretch)- 2 Passive Component and 1 Contractile: Parallel elastic component (PEC) Passive elasticity derived from muscle membranes… Supplies resistance when muscle passively stretched. OR, Series elastic component (SEC) Passive elasticity derived from tendons… Acts as spring to store elastic energy when tensed muscle is stretched Primarily elasticity derived. Contractile Component = Muscle fibres., Irritability (Ability to respond to electrical/mechanical stimulus), Ability to develop tension(Eccentric contraction Concentric contraction). Enthesis: Enthesis junction between tendon/ligament & bone Functions transfer mechanical tensile loads generated from ms-tendon complex to bone 2 types of enthesis Fibrous Fibrocartilaginous i.e. Patellar tendon. Factors Affecting Muscular Force Generation: Force-velocity relationship… Length-tension relationship… Electromechanical delay… Stretch shortening cycle (SSC)… Type of muscle contraction… Freq of stimulation of motor unit… No. motor units & size. Strength gains occurs as mm growing wider not longer. Muscular Power: Product of muscle F & velocity of muscle shortening Rate of torque production at joint= Max power occurs at: ~ ⅓ max velocity ~⅓ max concentric F Affected by muscle strength & movement speed. Musculotendon Units (MTU) MTU = muscle fascicle + tendon Majority of MTU changes is the stretch & recoil of tendon This allows the muscle fascicles to generate force economically by optimising contractile conditions according to F-length & Fvel relationships. STRETCH SHORTENING CYCLE: 1. elastic recoil: Active muscle’s stretched or passively stretched muscle’s are suddenly activated. Tension in these muscle’s Increases. Thus, storage of potential elastic strain E in series elastic component of the muscle’s & muscle-tendon unit. Portion

of this stored energy is recovered & used to potentiate performance. 2. Stretch reflex activation: Instrumental in F & power enhancement during SSC. Important role in stiffness regulation & hence SSC. Contributing to efficiency of motor output by making F output more powerful. Rapid reflex-induced cross-linkage formation could play a substantial role in F generation during stretch. What do you think the role of eccentric training? Eccentric training increases ability of musculotendinous unit to store & produce more elastic energy. Principle of conservation of momentum: In the absence of external forces, total momentum of a given system remains constant. Why is catching a ball is easier when the hands move at vel in same direction as ball, but with slightly lesser magnitude? 1. Lower resultant impact velocity slows the vel at which the ball would rebound in the collision with the hands thus easier to time clasping of the hands 2. Impulse-Momentum r/ship. Coefficient of Friction: Index of interaction between 2 surfaces. Unitless number. Relative ease of sliding or amount mechanical & molecular interaction. Coefficient of static friction (µs). Coefficient of kinetic friction (µk). Positive Work = net ms T & direction angular motion in same direction. Concentric muscle contraction > E expenditure than = amount negative work. Negative Work = Net muscle T & direction angular motion in opposite direction and/or Eccentric muscle contraction. 3 factors affect Angular Momentum: 1. • Mass (m) 2. • Distribution of mass with respect to axis of rotation (k) 3. • Angular velocity (ω). Parallel Axes Theorem - MOI Parallel axes theorem: Any object that rotates has a MOI Leg swinging about the hip joint has a MOI, as does any body segment that spins about its own axis. Thus, body segment to have 2 x MOI Local = MOI of a body rotating about its centre of mass (ICOM). Remote = MOI of a body rotating about its external pivot = mk2 . Total inertia (Itot) = ICM + mk2. Angular Momentum (H) So to calculate the angular momentum of the lower limb we multiple the MOI by its angular velocity for both the local & remote terms. Conservation of Angular Momentum: Cat lengthens it lower limbs to increase MOI & brings it upper limbs towards axis to lower MOI B. When it rotates, the lower limb (with higher MOI) only has to rotate a small amount in the opposite direction C. Brings it lower limbs in lower MOI & lengthens it upper limbs to lower MOI to rotate the lower body. What is the purpose of arm swing in running? L leg start back-down while still flex, mass moving slowly as it takes time to accel it thus L leg highest vel just before IC A. arm mass close to body (small k) & small vel thus small H. B As leg extends increased H so to counteract this the arm extends (increased vel & k) to increase H (this should be vigorous) C. During foot-ground contact, lower vel legs & H ∴ arms counteract H via flex elbow to change k & lower vel. Anatomical Pulleys: Changes angle of pull of muscle providing F Thus Increasing in angle of pull and thus increasing rotary component Eg. Patella for quadriceps. Body is built for speed & ROM as predominately 3 rd class levers Concentric muscle action is typically a 3rd class & eccentric muscle action is typically a 2nd class lever – BUT this is not always the case! Mechanical advantage: MA < 1 = advantage speed/ROM Wheel-and-Axel: motive F applied to wheel MA = radius wheel/axis radius = F axis/F wheel Pulleys change effective direction of applied motive F. GRF during Running: 1. Ft travel forw rel to body & ground 2. Ft is stationary rel to the body, but bc body is still moving forw, ft is also moving forwards relative to the ground 3. Just before IC, ft moves backw rel to body, but is still moving slightly forw rel to ground thus forw F applied to ground (Newtons Law Action & reaction) therefor = breaking F 4. Ft is no longer applying a forw F 5. Ft is able to produce a backw F thus back F = propulsive F. Anteroposterior Impulse: Propulsive

impulse: • Variance in sprint vel: 57% sprinters, 27% team sport • Max to propel forwards • ….but too much may lead to greater ground contact time & lower step freq. Breaking impulse: • Min to max forward vel • Weak r/ship - breaking impulse & sprint vel. Propulsive impulse(case study) Marion Jones (USA): Greater hip extension allows ft to travel far past the body thus greater time for F application thus greater propulsive impulse Short contact times (~0.11 s) = high speed of her body over the ft + placement of her ft only slightly in front of her body at IC. Touch Down Angle: Higher braking impulse with Higher touch down angle Total positive AP impulse (braking + propulsive) is smaller so acceleration is lesser. Elite sprinters land with their foot about 6 cm in front of the body. Novice sprinters might land with their foot about 2x that distance in front. Torque: moment of force. Rotary effect of a force. Angular equivalent of force = force multiplied by perpendicular distance from force’s line of action to the axis of rotation. Force in Newtons times distance from rotational point.

Rotary component of troque: Muscle F directed perpendicular bone produces torque or rotary effect. Maximum when muscle oriented 90° to bone. Change in angle of orientation from 90° in either direction thus lowering it. How Can you Locate the COG? 1. Balance Method 2. Reaction Board Method 3. Segmental Method. How do you Increase body’s stability? 1. increase body mass 2. increase friction between body & surfaces of contact 3. increase size of the BOS in direction of external F 4. Horizontal positioning COG near edge of BOS on side of external F 5. Vertical positioning COG as low as possible.

Greater length of swinging implement means Greater linear vel But Greater MOI & makes harder to achieve same ang vel. With Baseball bats. POLE VAULTER COM: Extended position as leaves ground COG close to bottom of pole Pole bends thus lower distance between vaulters COG & bottom of pole lowering MOI of pole at its bottom end Facilitates rotation of pole towards mat. Once sure he has enough ang displacement to go over bar, he wants to increase rotation his rot on pole but lower rot of pole Tucking & moving COG to handgrip (axis of rotation body) lowering MOI of body & helps rot increase MOI of pole as vaulter COG has moved farther from bottom of pole. Slows rot of pole towards mat. -If all other factors are held constant, if you decrease the radius of rotation at which a swinging implement hits a ball, the linear velocity imparted on the ball will decrease. -The greater the impulse the greater the change in momentum and the greater the jump height. -The optimal take-off angle for long jump depends on the take-off speed. -Tangential acceleration is the component directed along the tangent to path of motion.

How can you make sure you continue to move forwards in such a collision ? You must have a greater momentum going into the collision. Since your body mass is smaller, you’d have to have a greater velocity. We can work out the velocity at which you would exactly match your opposition and the velocity above which you would knock your opponent backwards. Your velocity is represented by ‘v ’, so we need to re-arrange the equation to calculate this number with the total final velocity of the system (v) at zero. 2 Friction definition: Force acting over area of contact between 2 surfaces in direction opposite that of motion or motion tendency. Max static friction(Fm) • Max amount friction that can be generated between 2 static surfaces. Kinetic friction (Fk) • Constant-magnitude friction generated between 2 surfaces in contact during motion • greater max static friction. Openk i net i cchai n:Themos tdi s t alseg menti sf r eet omo ve ;@ pi t chbas ebal l@ t hr owFr i s bee@ bar bel lcur l .Cl os edk i net i c c hai n:Themos tdi s t alse gmenti sSt at i onar y ;l es smo bi l i t y ;@ pus hup. 1st class level = forces on either side of the fulcrum. 2nd class lever= favours force production. 3rd class level= favours speed and ROM....