Movement science notes PDF

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Movement science Module 1 (intro) What is movement  Movement occurs due to an interplay between skeletal, muscular, nervous, respiratory, cardiovascular, skin and immune systems  A structure will move depending on the forces applied to it and what it is composed of Biomechanics

Forces acting on the body Body is made up of from:       

Bones Ligaments Tendons Muscles Nerves Control centre Fascia

Normal or optimal movement

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 Using the term ‘abnormal’ movement will create a negative/un-positive stigma surrounding the patients condition Optimal movement o Smooth and efficient o Without breath holding or compensations Limits of optimal movement o Active subsystems:  Muscle weakness, rupture, pain o Motor subsystems  Damage to nerves and brain o Passive subsystems:  Increased movement (joint laxity)  Decreased movement (joint surface disruption reducing the normal gliding and rolling of the joints e.g. OA), scars and adhesions

All three subsystems need to work effectively and efficient for optimal movement, while considering the environment + individual.

Passive subsystems – Bones/joints

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Bones have an essential structure which allows or limits movement Bones must be strong so that they do not bend when loaded and flexible to absorb energy by elastic and plastic deformation o Bones fail if they don’t bend or absorb energy The skeleton is a system of levers that rotate about fixed points when force is applied o Degrees: measures angular displacement

Ligaments + joint capsules 

Role - connect bone to bone and guide bone movement

Joint-axis – centre of rotation Theoretical axis of rotation  

Joints move around an axis – for some joints it’s a moving axis Dynamic process occurring -> “to keep the joint centred” – maximising joint surface areas and joint stability o Dynamic process – force that causes it to change or progress

Factors Influencing Joint Motion  

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Internal forces acting on the bones around the joint o Muscles, ligaments, joint capsule around the joint External forces o Gravity + weight o Environment – city/rural o Context of movement – elderly/soldiers Joint surfaces Congruence o The more congruent the more stable = hip o The more incongruent the less stable = knee Internal factors o Motivation o Emotional

Active subsystems – muscle    

Every movement you observe is caused by resultant muscle force and gravity forces Muscles cause bones to move Muscles “create” strength and help stabilise joints Their role depends on their structure and attachment and how they pull on the bones around the joints

Element to consider during assessment + treatment approaches   

The individual – passive/active/neural subsystems Forces acting on the body – external + internal forces Context of movement o External environment o Internal environment (motivation/emotional factors)

How do we analyse movement? 

How to analyse movement, depends of why you want to analyse the movement o Outcome measures

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o Looking for a “deviation from normal” o Research tools Can use: o Observation – describe the movement from starting position, the movement itself and the finishing position o Technology – apps, 3D movement analysis

Sit to stand essential components      

Foot placement behind knee Ankle dorsiflexion ROM Knee flexion varies with chair height Hip flexion varies with chair height Hip flexion prior to thighs off – max velocity at thighs off with extended neck and spine Ankle dorsiflexion (knees move forward)

Measurement of movement 

Through: o Length of steps + joint range (through movement) o Cause of movement – forces + moments (calculated from the outcome movement)  Therefore – targeting the forces that act on each body segment – that cause/affect the movement

Forces Force   

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All motion is subject to laws + principles of force and motion. Anything that causes or has the potential to cause movement (ex. push, pull, friction, gravity) Measured in newtons Force: o Internal (muscle contraction) o External (gravity + contact with another body, or being in water) All forces have an amount, direction, point of application and line of action Vector quantity

Analysis of human movement  

Vector – quantity that possesses magnitude and direction o Ex. force Scalar – a quantity completely defined by magnitude o Ex. temp, length, area, volume

Equilibrium    

Refers to a system that is stationary All forces add up to zero System is balanced No movement is occurring

Free body analysis  

Way of simplifying problems By breaking down forces acting on a body segment or whole body depending on what you are looking at analysing

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Solving the problem o Isolate the body of interest o Sketch the body + external forces o Add the forces + moments to zero o Solve for unknown force

Vector analysis 

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Info required: o Magnitude o Direction o Point of application o Line of action For muscles – direction of force is along its line of action + point of application = attachment to bone lever Gravity force (always downward), point of application is the centre of the mass = centre of gravity – line of action is downwards

Addition of forces 

When analysing systems in equilibrium, forces are added as vectors o Direction + point of application is critical o 2D/3D forces – requires use of simple trigonometry

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Adding force vectors together -> results in finding the resultant force

Therefore, use the triangular method

Parallelogram  

Forces are placed end -> to -> end and drawn to scale Resultant force is calculated, by measuring the resultant length

Tip to tail method

Forces acting on the body 

Forces can be represented as vectors

Forces: o Muscle force o Joint reaction force (force of 2 bones applying to each other) o External resistant forces (ex. gravity, weight holding)

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Force application Ground reaction force – the resistance that the ground applies to the body Joint reaction force – force of two bones that are applies to each Friction – force created when one surface moves over another Fluid resistance – force of the water against the body Inertial force – a force opposite in direction to an accelerating force o Ex. ankle keeps on swinging forward in running (Newtons 1st law) Elastic force – force that occurs as a deformed object (spring) – tries to return to original shape o Material changes in length when force is applied to it ex. trampoline

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Torque o o o

The rotational force The force that can cause an object to rotate about an axis Forces will act upon a joint to cause movement (internal torque)

Moment arms Refers to the length between a joint axis and the line of force acting on that joint  

Forces can act at a distance to the fulcrum/centre of rotation The distance of how far they are from the centre of rotation – determines how much of an effect they have – on the rotational force (torque) that can be generated Torque = rotational force Torque = force x distance

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Forces act on the bones to rotate the joints Variables: o Amount of force o Distance between joint axis + point of force application Moment arm – is the perpendicular distance from the point of force application o Varies depending on position of joint -> therefore the amount of rotational force/torque will vary Joint angle varies: o The moment arm varies o The torque generated varies by the muscle (ex. biceps) varies Movement is created by forces (muscles/gravity) acting on levers (bones) around joints Movement occurs due to rotational forces Movement = sum of all torques

Varying effect of gravity 

The force of gravity can have a rotary or longitudinal effect when acting on the skeleton

Direction of muscular force

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Not all forces act perpendicular to the lever The angle of insertion changes with joint movement

Force applied to a pivoting structure Effect of muscle force 

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Direction of resultant force: o Compression of the joint o Joint distraction (creates more space inside the joint complex) o Rotation of the bone around the joint Situation of 2 muscles acting around a joint o They could cancel each other out = causing no movement o Could increase the movement or have another effect

Components of force 1. Rotatory (produces torque) 2. Longitudinal/translator o Compressive o Distracting o Usually stabilising (except in pathological states) Measuring muscle force  

By invasive force transducers Simulations in cadaver models

However – by looking at forces/free body diagrams it allows us to model and predict forces and understand joint mechanics (without the above unnecessary tech) Question – what is the force of quads needed to keep this man stationary (equilibrium) position? Body weight x distance line of gravity to knee joint = torque of quads x distance pulling force of quads to knee joint Body weight is stable the moment arms are stable

Centre of gravity Centre of mass and centre of gravity Centre of mass = the single point where the entire mass of an object can be considered to act for the purposes of estimating its position  Precise motion will change with the position of the limbs (growth/weight)  Differs depending on muscle mass Centre go gravity = the point at which all the weight of the body is concentrated  Lies approx. S2 (anterior to sacrum)  Different body positions may alter the COG falling inside/outside of the body  Important for balance

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Base of support Reliant on:  

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Area – bound by outermost regions of contact between body and support surfaces Line of gravity o Stable = within BOS o Unstable = outside BOS Small BOS = less force  unstable Height COG relative to BOS o Increases with angular displacement  increased torque

Centre of gravity  

An imaginary point inside/outside the body, which the body/object is balanced Locating COG o Segmental method  Use data for average locations of individuals body segment’s COGs as related to % of segment length  Then calculate through the equations below

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New COG will become closer to heavier segments

Balance method  Segment balance point in 3 different planes

Stabillity  

For an object to be stable its LOG must fall within BOS Factors affectng stabillity o Larger BOS = greater stability o Lower COG = more staillity

Free body diagrams The diagrams are snap-shot in time – body is not moving, therefore is in equilibrium and all the net forces sum to zero

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Solving problems: 1. Isolate body of interest 2. Sketch the body and all external and internal forces  Ex. external forces (HAT), internal forces (quads) 3. Sum the forces and moments to zero 4. Solve for unknown forces Torque = F x D F(weight) x moment arm = F (muscle) x In moment arm F(weight) x Ex moment arm = F (muscle) If Ext moment arm is smaller, than the Force the quads are required to generate will be smaller

Levers in the body Lever   

Consists of a rigid body with two externally applied forces and a point of rotation The 2 forces can either me the same or opposite sides of the centre of rotation (COR) 3 classes of levers o First, second, third

Human body as mechanical system   

Joint = axis Bones are levers Forces acting on bones o Internal – muscles o External – gravity/added weight etc.

Mechanical advantage   

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Refers to when the levers can be used so that a small force can move a greater force A measure of the output force to input force in a system The ratio of distances o If >1 then = mechanical advantage o If < 1 then = mechanical disadvantage Ex. small changes in biceps muscle length – produce movement at the distal lever through a greater arch at a fast speed Mechanical advantage magnifies the force effect

Levers First class levers     

Fulcrum/COR is positioned between the force and the resistance An equal amount of effort is required to move an equal amount of resistance Ex. see-saw Fulcrum of the lever is exactly halfway between effort and resistance the mechanical advantage will be 1 Examples; triceps o Fulcrum – elbow joint

o Load -forearm o Inserting into olecranon o Post-humerus  Head extensors (upper cervical spine) o Fulcrum – cervical joints o Load – head o Inserting into occiput  Trunk side flexors o Fulcrum – lumbar spine o Load – upper body Second class levers Resistance is between fulcrum and effort (force) The closer the load is to the fulcrum = the easier the load is to lif Mechanical advantage >1 o Allows for large force generation o Force advantage  Ex. wheelbarrow  Ex. rear molars + jaw o Fulcrum – jaw o Load – food

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Third class levers    

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Force (effort) is between the resistance and the fulcrum Allows great movement Speed and range of movement – most muscles operate this way Mechanical advantage fibres (collagen) crimped up in rest state, begins to unwind once stretching begins (toe region), original length of fibres change will return to original length to the yield point. Afer the yield pint, tearing of the collagen fibres occurs (permanent damage) – plastic region, failure point involves the entire tearing of the ligament.

Hooke’s law Stress applied to stretch or compress is proportional to the strain. 

When a material is loaded, in the elastic zone, the stress is proportional to the strain o Object will return to original shape afer the afer the load is removed

How materials respond to loading 

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Mechanical properties of materials vary due to o location, its use, ageing, immobilisation (ex. cast – change to tissue - strength), pregnancy, diabetes, NASIDS (effect on inherent structure of tissue) Response to loading depends on: o Load magnitude o Duration o Prior loading Affected by – amount of water in extra cellular matrix Loads can be modified by changing the shape, size, strength of the tissues – bone, ligament, tendon etc. Tissues will adapt to the loads placed upon it - changing size and shape o Sedentary lifestyle –

What is stiffness   

Rigidity of a material in response to an applied force Relates to slope of linear region (elasticity) – young modulus measured as unit of pressure – Gpa Relates to the structure of the material

Due to viscoelastic property of the material the time the load is applied leads to a change in the material 

Low load over - long duration, leads to: o Stress-relaxation  Decreases in stress that occurs when a material is held under load at a fixed length o Creep  Low load over long time, will deform material and is affected by increase in temp  Increased temp combined with low load – tissues will reach point of strain quicker (changing length of tissue)  Stretching of heated tissues doesn’t take as long when compared to cold tissues  Ex. serial casting -> children walk ontop of toes (tighten Achilles tendon) – cast – with a stretch in dorsiflexion, to bring heel down to ground – low load over a long period of time

Mechanical failure   

Relationship between stress at failure to no. of cycles that will not cause failure Failure can be caused by a big force or multiple reloading Ex. paper-clip – one bring force – can evoke the fatigue point quickly

Load to failure – ultimate strength is the largest stress a material can sustain before it breaks Fatigue fractures – repeated loading at low loads

Hysteresis   

Lagging behind – when applying a load and unloading it – how much energy is lef behind (ex. heat) Tissues response to loading and unloading Describes the amount of lengthening/heart a tissue will maintain afer a cycle of stretching

Ductility vs brittle  

Ductile – a material that is permanently deformed to a large extent before it ruptures (high ductile, >6% elongation) Brittle – a material will break before it become permanently deformed (

Mechanical properties of cartilage Cartilage  

Deforms under constant loads Function of fluid flow from matrix o Initially rapid o At equilibrium – fluid flow zero

Types of cartilage 

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Articular – hyaline o Load bearing o Found in synovial joints ex. hip, knee, elbow Fibrocartilage (elastic) o Assists with shape of structure o Yellow fibrocartilage – ex. ear/trachea o White fibrocartilage

Articular cartilage   

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High specialised connective tissue suited to withstanding high joint loads over an individuals life-span 3 layered structure allowing for greater dispersion of forces Primary functions o Distribute load over a large area therefore decreasing stress on joint surfaces  Increased surface o Minimize friction between joint surfaces Composition o Composed of cells called – chondrocytes o ECM – water (70-80%), proteoglycans, collagen o Proteoglycan/water content very through tissue Locations o Near articular surfaces  Superficial (10-20% thickness)  Collagen fibres parallel to surface – densely arranged  Water content high  Proteoglycan content low o Middle of the cartilage  Middle zone – 40-60% thickness  Fibres randomly/sparsely arranged

Deep zone  Fibres arranged in bundle – that fix cartilage to subchondral bone via an interlocking root system Fluid flows through pores in the cartilage in response to deformation , the cartilage closest to the surface, has the highest permeability- this decreases at the deeper levels Immobilisation and unloading – reduced fluid flow resulting in decreased nutrition and deformation Articular cartilage does not have a blood supply and because of this is unable to utilise the wound healing process and this limits the potential of cartilage to repair o

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Clinical relevance of permeability 

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Deformation o ^ Dependent on permeability - a valuable mechanism for maintaining load sharing between the solid and fluid phases of cartilage. If fluid flowed easily out of tissue then the solid matrix would bear the full contact stress, thereby being more prone to failure Intermittent loading is beneficial for cartilage – for fluid to be pumped through cartilage

Ability of cartilage to repair   

Avascular therefore unable to follow standard wound healing process. o No local inflammatory response…. If aggrecan is lost from the Extra Cellular Matrix the tissue can replace the lost PG If the collagen network is damaged there is limited ability to make a long-lasting repair

Osteoarthritis OA process involves the loss of balance between the synthesis and degradation of macromolecules that provide articular cartilage its biomechanical and functional properties o

Wearing out of the cartilage

Structural breakdown of cartilage begins focally at sof patches in the collagen network and spreads to larger areas of cartilage. This leads to lesions in the cartilage surface, which develop into fissures and pits, thus making the articular surface uneven. Featu...