HSE323 T2 2024 LECTURE NOTES.docx

**[HSE323 T2 2024 LECTURE NOTES]** **WEEK 1** [Lecture 1: Intro ] Biomechanics Goals - Improve human performance - To improve health - Prevent injury - Minimise injury - Help prevent/minimise effects of chronic health conditions Specialties - Sport - Footwear - Surfaces/equipment - Clinical - Biomedical - Occupational Lecture 2: Kinetic Analysis **ULO\'s** 1. Identify the different measuring devices for kinetics 2. Understand how these devices can be used to measure kinetics 3. Appreciate how these devices can be used in clinical and sport biomechanics 4. Understand the advantages and disadvantages of each measuring device. **Lecture notes** - Kinetics: analysing forces that are present, pull or push action, that is acting on the body or an object. - External forces: reaction force and action force. These can be measured using force plates, force transducers or dynamometry (this is spelt role) - Action force: eg: push down onto the ground - Reaction force: force coming back to the object - Internal forces: shear, compression and joint reaction force. - ![](media/image2.jpeg)Forces in controlled landing is generally no higher than a 5x bodyweight, uncontrolled landing will be between 6-11x bodyweight - Joint reaction force is a force generated in a joint in response to forces acting on the joint, eg: compression, loads, muscle forces, moments and torques. Use EMG to measure this. - Torque is produced by muscle and acts upon a joint, it is also referred to as a moment. *T = linear force x perpendicular distance* - When we move and our body is trying to stabilise: There are usually both positive and negative torques/moments acting across joints being generated by muscles. With ground reaction forces, there will be both external and internal torque occurring to counteract each other and keep the body stable. External torques are generated by the GRF. - Force plates are most commonly used to measure kinetics external forces. Will measure 3 different directions: vertical, horizontal and mediolateral/sideways - Most force platforms are built into floor surfaces. [Measuring Kinetics Overview ] +-----------------------------------+-----------------------------------+ | ***Measure*** | ***Method*** | +===================================+===================================+ | **Ground Reaction Force** | Force Plate | +-----------------------------------+-----------------------------------+ | **External Force** | Strain Gauge and Force Transducer | +-----------------------------------+-----------------------------------+ | **Acceleration Loads** | Accelerometers and Inertial | | | Measurement Unit | +-----------------------------------+-----------------------------------+ | **Joint Reaction Force** | Force Plate + 3D Kinematics | | | (inverse dynamics) | +-----------------------------------+-----------------------------------+ | **Joint Torque/Moment** | Force Plate + 3D Kinematics | | | (inverse dynamics) and Isokinetic | | | Dynamometry | +-----------------------------------+-----------------------------------+ | **Muscle Activity** | Electromyography | +-----------------------------------+-----------------------------------+ | **Muscle Force** | Handheld Dynamometry and | | | | | | Force Plate + 3D Kinematics | | | (inverse dynamics) | +-----------------------------------+-----------------------------------+ - Force plates measures the overall load on the body. Vertical Load (Fz), Medial-Lateral (Shear) Load (Fx) and Anterior-Posterior (horizontal) Load (Fy). From this, you can calculate the resultant load - Ground Reaction Forces: shows patterns observed for rearfoot running pattern (photo). Left is vertical forces, right is horizontal. There is an initial impact peak and then active peak which is the propulsion at toe off. In the horizontal, the initial is a negative force which is when you\'re breaking, the propulsive phase generates a positive force as you move forward. - Centre of mass can be used as a measurement and is measured using motion analysis. May be measured by a pressure mat too - Centre of mass and pressure patterns can be used to assess fall risks in older adults. - Centre of pressure: typically look at sway in the anterior posterior and medial lateral directions. Doing it with eyes closed, eyes open single leg and eyes closed single leg. Can be used for concussion patients. - Inverse dynamics: GRF\'s are essential in order to determine joint torques for a link segment model via inverse dynamics (this isn\'t super touched on in the unit). To do this type of testing you need: GRF\'s, kinematics, gravitational forces, segment mass, centre of mass, joint centre and moment of inertia. - Force Plates\ Advantages: accurate, sensitive, 3D, high sampling rate and allows various measurements\ Disadvantages: expensive, need to be isolated, data can be limited by the effects of targeting, the lab plates are not portable and portable plates aren\'t as reliable. - Strain gauges/force transducers: they can be used to measure forces exerted onto objects - A strain gauge is a type of force transducer. It measures strain (change in length/original length). Acts like a spring. When the spring is compressed, the length decreases and the diameter increases, increase the materials resistance. Changes in the materials resistance creates an electrical change that can be measured. - Accelerometers: measures acceleration and is an indirect measure of force. - Inertial measure unit: one sensor that combines 3 tools. Measures acceleration, rotation and direction - Accelerometer\ advantages: lightweight, very portable and gives in field measurements\ disadvantages: not a direct measure of force, less accurate, low load threshold and mass/size. - Isokinetic dynamometry: measures force in open kinetic chain movements. Measures force at a constant angular velocity\ Advantages: allows multiple measures, controlled velocity and can isolate joint of interest\ Disadvantages: expensive, not portable, open chain movements only, limited multi joint movements and limited stretch shortening actions - Handheld dynamometry: clinical measure, limited to isometric contractions (Leroy used this to test my hip) - Pressure measurement: looks at the pressure between 2 surfaces in contact.\ Advantages: portable, provides kinetic, temporal and spatial measures, provides detailed pressure information broken into regions\ disadvantages: expensive and isolated to one area. **WEEK 2** [Lecture 1: Motion Analysis ] ULO\'s 1. Know the different devices for kinematics 2. Understand how the devices are used for measurement 3. Appreciate their application to clinical and sport settings 4. Understand the advantages and disadvantages of each device - What is kinematics? Measuring quantities describing movement, eg: position, displacement, velocity, etc - Motion analysis is used to quantitatively examine human movement in 2 or 3 dimensions - Kinematics measures: linear and angular displacement, velocity and acceleration, asking how fast? How high? How long? What angle? - Kinematic analysis: if change in position and change in time between images is know, then we can calculate the derivatives, velocity and acceleration - 2D kinematics is often used, eg: walking/gait analysis - 3D analysis is used for more clinical and complex problems, eg: cerebral palsy children - Using 2 or 3D is dependent on the situation. - 2D analysis: planar movements, looking at the movement from one viewpoint, camera needs to be perpendicular to the motion (at a right angle), need to calibrate image using known markers or object to perform linear kinematic measures. In these, we rely on video cameras. - High speed cameras are a must for faster movements. This enables precise analysis of critical events - When using cameras, you must be perpendicular to the movement. If this is wrong, it\'s a parallax error - Perspective errors in arise from calibration errors. - Shutter speed is important. - Video basics: use a tripod, maximise the view of the performing, avoid influencing the movement, use the shutter for any action involving movement, add light if videoing indoors - 3D analysis: you want to look at a movement from multiple viewpoints. Automated systems are now more often used as opposed to manual camera set up - You need to be on point with marker sets and have multiple markers for accurate calculation. - Soft tissue motion analysis isn\'t something that is widely used at the moment. - There is work in markerless 3D motion capture and whilst promising, no validity is established Automatic Systems - Optoelectronic Techniques: participants wear infrared light marks. Camera has a special semiconductor diode surface, scans for pulsed light to locate marks, middle lens scans vertically, outside lenses scans horizontally, high accuracy and large frequency range. But they don\'t have a big measurement volume space. - Infrared Technique (Vicon): doesn\'t use visible light. Active infrared lights from a donut shape around the camera lenses. Pulses light. The light bounces off the reflective markers. Calibration is done with an active wand and is waived in the capture space. PROS AND CONS OF 2D AND 3D 2D - Is cheaper and simpler - Doesn\'t need as many cameras - Has fewer methodological problems and requires less digitising time - Is conceptually easier to relate to 3D - Involves more complex procedures and is expensive - Shows the body\'s 3D movement - Increased computational complexity - Allows angles be body segments to be calculated accurately - Raises the problem of which convention to use for segment orientation angles, which 2D analysis sidesteps - Enables the reconstruction of simulated views of movement Data Smoothing - Smooths data to eliminate error and this needs to be done before calculating derivative data, eg: displacement, velocity, etc - Smoothing works to decrease error in the maths process - There\'s different types of smoothing - You don\'t want data to be noising cause otherwise it isn\'t valid. Goniometer - Angular kinematic tool - Measures joint angle - Good with hinge joints - Advantage: inexpensive, quick and measures relative joint angle - Disadvantage: heavy Accelerometers - Measures acceleration and angular velocity Timing Gates and Contact Mats - Measures time - Measures temporal features of movement - Easy to use once set up, inexpensive and reliable - Can be painful to set up, double triggered. [Lecture 2: Electromyography (EMG) ] **ULO\'S** - Know what EMG is and how it\'s used - Understand strengths and limits of EMG - Revise neurophysiology of muscle contraction - Understand the different types of EMG electrodes - Explain signal sampling and processing in EMG - Explain the relationship between muscle activity and muscle force **Lecture Notes** - EMG looks at the electrical signal of a muscle when activated by a motor nerve impulse - It is a kinetic measurement tool - Let\'s us measure the processes occurring within muscles and how they produce force and movement. - In biomechanics, the term muscle response as activity or activation is used instead of contraction *[What can we use EMG for? ]* - See whether muscles are active or not - Fatigue studies - Timing of muscle activation patterns - Force contribution of different muscles - Normal vs altered activation patters - Effects of training prescription of the neural muscular system *[Neurophysiology ]* - Nerve impulses are transmitted as action potentials down a nerve axon to the muscle fibres that it innervates. - A single axon can innervate between 3-2000 muscle fibres - Motor unit: a motor neuron, many branches of the axon and the muscle fibres - When an AP reaches the muscle, it propagates proximally and distally and is termed to the motor action potential - A motor unit action potential is a spatiotemporal summation of MAP\'s for an entire motor unit - Motor unit AP\'s have both positive and negative signals and zero signal. Resting is a negative signal and will then go through depolarisation to reach the positive signal and will then repolarise and go back down. - Muscle twitch: signal stimulus contraction relaxation sequence in a muscle fibre. - The AP is almost over before the muscle will actually twitch. AP coincides with the latent period of the twitch *[EMG Signal ]* - Algebraic summation of many repetitive sequences of MUAP\'s from all active motor units in the vicinity of the electrodes - Electrodes are the transducer that picks up the energy flow from the muscle fibres. It picks up the ionic flow and coverts it to electron flow. - Ionic flow has to do with sodium and potassium - We\'ve got surface and indwelling electrodes. One sits on the surface of the skin, the other is the needling that\'s inserted into the muscles, guided by ultrasound - EMG signal magnitude can be affected by: motor unit recruitment, fat overlaying muscle, muscle temp and muscle length and cross sectional area. - Surface EMG: measures from the skin.\ advantages: easy to use, comfy to wear and large detection volume\ disadvantages: cross talk, can\'t specify deep muscles and movement artefacts - Indwelling EMG: aka fine wire or intramuscular EMG. Must be gloved up when using these.\ Advantages: specify deep muscles, very specific, can detect MUAP\'s\ disadvantages: participant discomfort, can be too selective and can be dangerous under movement conditions. *[Skin Prep ]* - Shave area - Abrade the skin (exfoliate) - Clean with alcohol wipe - Let skin dry *[Processing EMG]* - Raw EMG gives valuable info but it\'s kinda useless in that form - Processing of the EMG signal enables extraction of into - Step 1: High Pass Filter. Removes any motion artefact and other low frequency noise - Step 2: Full Wave Rectification. Make all signals absolute values. Flip the negative signals and make them positive. - Step 3: Low Pass Filter (linear envelope). Removes any high frequency noise effecting the signal *[Other Processing Methods]* - Amplitude normalisation: EMG signal is normalised to an amplitude value. Enables comparison between muscles and/or individuals. Eg: max within a task like a sprint, max isometric voluntary contraction - Time normalisation: EMG signal is normalised to a task cycle, eg: gait *[Reporting Guidelines]* - Follow ISEK Guidelines. *[Interpreting EMG Data ]* - Not super simple - Small MU\'s are recruited first. - EMG amplitude is a function of MU recruitment and MU firing rate *[Isometric Contraction ]* - Usually consistent increases with contraction force (monotonic). Not adequately linearly related to each other. - Independent of fibre type and training - Non-linearity\'s include the influence of recruitment and firing rates Non Isometric Contraction - Less consistent than isometric - Influenced by: electrode movement, length tension relationship, possible reflex activity, change in number of MU\'s in detection volume and force velocity relationship EMG Fatigue Relationship - Alters force output and shape of MUAP - Average duration of MUAP increases - Lower conduction volume of MUAP - Tendency of the MUAP to fire synchronously instead of sequentially. **WEEK 3** [Lecture 1: Data Processing ] *ULO\'s* - Recognise that data has noise and error - Understand methods of reducing noise - Understand methods of data processing to eliminate noise - Refresh statistical knowledge and how it can apply in biomechanics - Understand how to determine reliability and validity of biomechanical measures *Accuracy, Precision, Validity and Reliability* - A: how close the measurement is to true value - P: how close measurements are to each other - V: the extent to which the values describe what they are intended to measure - R: how repeatable the measures are - Ecological validity: creating a testing environment that matches as closely as possible to the athletes training or competition conditions. - Movement variability: how precise the movement is that we are measuring *Types of Error* - Systematic: portion of the error that remains constant in repeated measurements of the same variable. Affects accuracy of the measurement, eg: incorrect equipment calibration, wrongly placed reflective markers, etc - Random: portion of error that isn\'t constant in repeated measurements of the same variable. Can occur when instructions have been misunderstood, testing is done on different days, etc. - All measurements of physical quantities contain some form of error. - Error isn\'t usually an accident or mistake, it\'s a result of the instruments that we use and factors out of our control - \*different types of error in desktop screenshots *Minimising Error* - How free of error our measurements need to be depends on the intended use of the results and the ability of the measuring tool to do it\'s job - Random error can give insight on the motor control of movement - Random error can often be overcome by increasing the number of data samples to derive a reliable measure. *Types of movement variability* - Strategic: - Execution: we need some execution movement variability so that we don\'t overload the joints exactly the same every single time - Outcome: performance outcomes. We want variability to be low here. *Noise and Error* - There\'s different types of noise - Noise can be due to movement of the skin under markers, particularly in high speed and flexible movements. - Can be due to vibration of marker attachments and camera movement. - Can be due to error in the 3D calibration process or not sampling at the correct rate - Static noise in wires or electronics used in the data collection process can cause error too. *Consequences of error* - Errors in primary (eg: time, position and force) measures will be magnified when differentiated or used in other calculations for secondary and tertiary (eg: velocity and power) measures - You need to filter at the first step *Methods to remove noise and error* - Place markers on bony parts of the body - Use good sticky things for the markers - Picking good cameras, i.e.; good image resolution - Place cameras on a stable base *Data Treatment Methods* - Curve fitting: using maths to smooth data, eg: 3 or 10 point average - Filtering/smoothing: averaging, eg: Butterworth filter - Polynomial functions: purpose is to reduce residual error. Difference between data points and makes a predictive line - Digital filtering: removes unwanted noise in signal. Benefits is that they can modify or remove the region of the power spectrum where the noise is known to be located. - True signal and noise will often overlap, therefore the correct filter should chosen conservatively. - The cut off frequency refers to the identified frequency that best separates the true data from the noise *Types of Digital Filters* - Low pass: trying to keep the low frequency signal and treat the noise in the higher frequency, often used for kinematic data - High pass: opposite of the above. - Band pass: works to treat low and high frequency and keep the movement data in the middle - Band stop: treats the data in the middle and keeps the outside data - Most filters are built into the software that we use *Cut Off Frequency* - Retains the true signal, eliminates noise - Can be identified through residual analysis, but we do try and avoid this. More so done in PhD stuff - Looking at those that have previous done something similar and see what filter they used. - Can graph frequency of the data and visually inspect it - Step 1: filter data through a range of cut off frequencies - Step 2: calculate the average difference between smoothed and raw data at each frequency that we have used - Step 3: draw a graph of the average error vs the different frequencies. Defined as the squared average of the residuals - Step 4: run a best fit linear regression of the residual - Step 5: draw a horizontal line from the intersection of the best linear regression on the y axis - Step 6: draw a vertical line from the intersection of the horizontal line and residual curve with the x axis *Further tips* *Roll off* - Filters don\'t chop data abruptly - The higher the order, the sharper the roll off - Some roll off is useful if you don\'t know the exactly start and end points Common data filters - Butterworth - However sometimes no filter may be necessary depending on what you\'re measuring Lecture 2: Applied Quantitative Biomechanics ULO\'s - Understand the role of a clinical vs sports biomechanists - Understand how they can be used to answer questions - Examine practitioner and research examples [Clinical ] - More common than sports - Gait analysis - Occupational safety - Injury/forensic - Production design and evaluation [Clinical Gait Analysis Service] - Cerebral palsy (this affects muscle tone, movement and coordination) - Spina bifida - Stroke - TBI and spinal cord injury - Neuromuscular disorders - Evaluating prostheses - Involves analysis movement patterns during walking or running - Typically uses 3D motion capture service, but some places will use 2D [Observational vs Computerised Gait Analysis ] *Observational* - Easy - Quick - Low cost - Subjective and low accuracy level - Single plane observation - Not well standardised *Computerised Gait Analysis* - Objective and highly accurate - Reliable - Multiple plane view and coordination between - Expensive - Long - Provides - Kinematic and kinetic information [Product design and evaluation] - Design and evaluate innovative apparel and equipment - Eg: body armour and military load carriage - More often in sport, used to evaluation footwear, eg: ASICS at Melb Uni. - Evaluating osteoarthrosis shoes. Knee osteoarthritis commonly affects the medial part of the knee and the goal was to reduce the moment of the knee with a wedge [Occupational Safety and Ergonomics] - Finding a way to make the workplace fit the person - Considers safety, comfort, easy of use, productivity, performance and aesthetics. - Eg: selling someone a bike. It needs to fit that person, not just pick a bike and then leave. [Injury and Forensic ] - Can support injury prevention, diagnoses and rehab - Forensic biomechanists determine whether an accident was the cause of alleged death or injury. [Sports Biomechanics ] - Difficult area to work in - Can you help improve performance and increase performance consistency? - Can you help reduce injuries so that athletes can more consistently train and compete? - Test selection criteria: relevance, validity, accuracy, reliability and practicality. - Sometimes testing younger athletes is better cause there is more variability than in older athletes. Barriers to the use of sports science by coaches - Transfer of sports science knowledge to coaching is poor - Overuse of jargon - Inability of researchers and practitioners to consider sports specific needs - Be prepared to: introduce basic biomechanics first, get to know the sport and it\'s culture and slowly begin to educate the coach. - Basic analyses can be quite effective when done with appropriate training interventions. **WEEK 4** [Lecture 1: Sport Performance Biomechanics] **ULO\'s** - To describe the role of biomechanists in sport - Identify various lab and field based equipment used and describe their application to sport Role of a Sports Biomechanist - The role is to help look at the science behind movement and why we move a certain way - Will often work with a multi disciplinary team 3D Motion Capture and Force Plates - 3D is the gold standard, especially if we want detailed kinematics - Force plates are good for when you need to determine impact, braking and propulsion, heel strike and helps to calculate joint forces and assists in calculating joint kinetics. - Force plates can be used in swimming too EMG - Measures muscle activation - Doesn\'t measure muscle force - We have surface or fine wire - Collects electrical potential between electrode sites Contact Mats OptoJump - Used to determine velocity and spatiotemporal characteristics of an athletes motion in real time - Optojump (I think this is like a timing gate) uses LEDs to detect disruptions between transmitter and receiver bars - Contact mats contain sensors that detect when a body is in contact with a mat Resistive/Assistive Sprint Devices - Portable resistance training and testing device - Cable giving isotonic resistance - Gives a smooth and controllable resistance up to 30kg - Measures power, force, speed and acceleration. Video Cameras - Used in comp environments - Captures footage at normal speed - Captures footage at high speed Calibration Poles/Cubes - Can be used when athlete movement occurs in one plane - Movement is filmed perpendicular Laser Doppler (Velocity Laser) - Used to determine the velocity characteristics of an athlete moving in a straight trajectory - Kind of like the manual speed checker - Can be used in field settings to get an instantaneous acceleration Inertial Measurement Units (IMU) - 3 axis measures - Looks at load - Accelerometers, gyroscopes and magnetometers. - Gives an indication of the load experienced by the muscular system Pressure Mapping - Is particularly useful in wheelchair athletes - Looks at different pressure points [Lecture 2: Sports Injury ] ***ULO\'s*** - Define injury, mechanism and various categories of injury - Describe the common causes of injury including the inciting event and intrinsic and extrinsic risk factors - Injury: damage (caused by physical trauma) sustained by the tissues of the body. - IOC injury definition: any musculoskeletal complaint incurred due to training and/or competition that receives medical attention regardless of the consequences with respect to absence from training or competition - Pain: resulting from participation in physical activity that causes a reduction in activity or need to seek medical device. - IOC pain definition: tissue damage or other derangement of normal physical function due to participation in sports, resulting from rapid or repetitive transfer of kinetic energy - One of the key things look at is the prevalence of the injury or pain in a population at a particular point in time. - Incidence: the rate of the occurrence of new or recurring cases of a condition or injury with respect to exposure. - Mechanism: the fundamental physical process responsible for a given action, reaction or injury Mode of Onset - The age of injury where injury may result from and there\'s 3 major types 1. Near instantaneous: exchange in large quantities of kinetic energy, eg: 2 athletes colliding with each other 2. Gradual accumulation: low energy transfer over time, eg: causing bone stress injury 3. Combination of both models: eg: repetitive training regime resulting in tendon weakness that then manifests acutely as a tear from acceleration forces applied during a single jump Types of Injuries ![](media/image4.png) - Aetiology: the study of causation or origination - Stress = load/cross sectional area of the tissue - Strain: amount of deformation Force/Load Directions - Compression: force along the axial plane (top to bottom) - Tension: pulling forces along the axis - Shear: force is applied parallel in the object, causes sliding and displacement - Torsion: causes twisting, typically one end is fixed and the other is moving - Bending: atypical loading pattern, load is different on one side to the other. Types of tissue injuries - Abrasion: skin tissue injury, usually the result of a shear force. Eg: scrap against concrete - Contusion: injury to underlying tissue, usually a bruise on the muscle. Typically result of a force from a blunt object. - Laceration: cut or tear in the skin having rough edges. Forces due to a sharp and/or hard object - Strain: an elongation of muscle or tendon beyond the elastic limit, where actual tearing or breaking of some fibres is present. Excessive tensile force. - Puncture: s small break in the skin from a pointed object. Force that is perpendicular to the skin and focused on a small area - Sprain: stretching and tearing of ligaments or capsular tissue. Tensile, shear or rotary force that pushes the tissue fibres beyond the elastic region - Inflammation: irritation or swelling causing pain and additional friction. Usually a repeated micro trauma due to tensile strain for muscles and tendons. Will involve shear and compressive forces on joints, eg: tennis elbow - Fracture: disruption to normal matrix of bone tissue. Caused by shear, compression, torsional or tensile forces. Or a combo of them. - Subluxation: partial dislocation. Injury to a joint which forces it to move beyond it\'s normal limit of motion. Usually due to a tensile or compressive force, with some shear to torsional force. - Dislocation: more severe injury where articulating bones have lost their alignment. Force may be tensile or compressive and usually involves some shear or torsional loading. Hamstring Strain - Grade 1: simple pull/elongation of the muscle - Grade 2: partial tear - Grade 3: avulsion/complete tear. Lateral Ankle sprain - Grade 1: stretching, small tears - Grade 2: larger but incomplete tear - Grade 3: complete tear Impact Force Fractures (Direct) - Forces from outside the body - Transverse fractures: these occur at a slight angle. Tapping mechanism, small forces over a small area - Crushing mechanism. Large forces over a large area. Results in an extensive comminuted fracture - Low or high velocity impact results in a comminuted fracture but more penetrating style. Active Force Fractures (Indirect) - Due to active forces originating within the body - Traction mechanism: transverse or avulsion fracture as a result of tensile loading. - Bending mechanism: bending occurring of the bone causing either an oblique or butterfly fracture - Rotational mechanism: occurs due to torsional loading causing a spiral fracture. - Transverse and oblique fracture: combo of loading patterns causing axial compression and angulation. - Angulation with torsion and axial loading causing a compound fracture. Injury Control Process 1. Establish the extent of the incidence and severity 2. Establish the aetiology and mechanisms of the injury 3. Introduce a preventative measure 4. Assess its effectiveness by repeating Step 1 Injury Reporting Scale - Level 1: niggles/pain - Level 2: modifications in class - Level 3: off class \< 3 days - Off class \> 3 days General Model of Injury Causation ![](media/image6.png) Dynamic Recursive Model of Injury Intrinsic Risk Factors (internal) - Factors within an athlete that predisposes or protects them from injury, eg: anthropometry, movement biomechanics - Common ones are knee alignment. This commonly looked at in landing screenings of ACL injury Extrinsic Risk Factors (external) - Factors outside of the athlete that predispose or protect the athlete from injury - Eg: shoes, surface, weather, rules - Sand or grass actually reduce the ground reaction forces in comparison to concrete. **WEEK 5** [Lecture 1: Biomechanics of Biological Tissue, Pt.1] **ULO\'s** - Understand the types of loads experienced by the body - To define stress and strain - Explain stress/strain graphs and key information that can be gained from these - ![](media/image8.png)Define viscoelasticity and the properties of these materials *[Types of Load ]* - Compression - Tension - Shear - Torsion - Bending Tibia fraction example - Oblique fracture pattern. - This would be due to a bending load. Tension on one side and compression on the other Combined Loads - Eg: hip joint. Combo of bending and torsion on the hip joint. - The hip joint is subject to compression when we walk or run. The bending force is due to the muscles around the joint. - Our glute med is important and helps to neutralise the compression forces and causes increases in tension. - When we contract the glute med, the compression force becomes dominate and reduces the tension, helping to reduce injury risk at the hip joint. *[Stress and Strain]* - What load is being imposed? We look at strain curves aka, load deformation curve - Strain: measuring how much the material has changed in response to the load that is being imposed. Eg: shorter or longer depending on the load. Analysing the quantification of the deformation of a material with loading. If it loses length, that is negative strain. A pulling on the material, increasing length, results in positive strain. - Stress: the affect of the force being imposed divided by the cross sectional area of the tissue in question. Internal resistance to external loads. - Immobilisation has a dramatic effect on vertebrae. It will only withstand a certain load, up to a certain point. - Stress = Force (N)/Area (cm2) - O (the little greek one) is used to denote compressive or tensile stress - T (the little greek one) is used to denote tangential (shear) stress - Linear strain: strain occurring in one axis (one direction) - You can have strain occurring in 2 different directions aka Poisson\'s Ratio. How much strain is occurring in the transverse and axial direction. Cause it is dimensionless, it has no units. Example of this load is the vertebrae. There\'s compression on different points depending on how we\'re moving. - Poisson\'s ratio is.22 in a healthy vertebrae. - Strength: the ability to resist applied stresses without failure. It\'s quantified as the max load sustained without failure. Strength is dependent on the direction and rate of loading. - Linear strain and stress can be assessed using a mechanical testing machine. It has 2 attached points and will measure the change in the length of the tendon and the change in electrical stimulus, therefore change in force. - Mechanical tests generate stress-strain curves for the materials being tested. - You can have pliant and stiff materials. A stiff will have a high gradient, will be able to withstand higher loads but can\'t change shape. Something like an elastic band would be the opposite. - Yield point: the elastic limit. - Failure point: point of no return and the material breaks. - Residual strain = new (altered) length - original length. Eg: after you stretch a hair tie way too much, still useable but doesn\'t have the same strength. - In between the yield and failure point, we have an ultimate point. This is the max level of strain that it can withstand. It won\'t necessarily break at this point, but it\'s at it\'s limit. - Stress strain curve 1, 2, 3 principle: 1. Slope: tells us its elastic modulus and stiffness 2. Regions: elastic and plastic 3. Points: yield, ultimate and failure. 4. Mechanical energy: another way to study materials when materials are loaded elastically, this is the triangle under the stress curve. ME = 1/2 x stress being imposed x strain - Viscoelastic Materials: eg: ligaments or tendons. Have extra properties and have non linear stress/strain characteristics and the ability to stretch of shorten over time. Viscoelastic materials show the following properties: - Hysteresis: stored mechanical energy that is lost when being loaded and unloaded. - Creep: viscoelastic material can mechanically creep when exposed to constant load. The continuous load will continue cause creep and continuous deformation over time. Can also occur due to increases in temperature. - Stress-relaxation: material undergoes constant strain over time and will relax over time to then reduce the stress on it and protect it from damage. - Strain rate dependency: not just how much stress and strain is imposed, but the rate at which it is imposed. Acute loading: application of a single force of a high magnitude resulting in injury Repetitive loading: repeated application of lower magnitude forces that results in injury later down the track. Eg: overuse injury [Lecture 2: Biomechanics of Biological Tissue, Pt. 2] **ULO\'s** - Understand the properties of bone and cartilage - Understand the effect of different loading conditions on bone and cartilage health - Understand how the material and structural organisation of bone and cartilage affect their ability to withstand mechanical loads. BONE - Mineralised collagen fibrils are the building blocks of bone - Woven bone: fibrils arranged in random orientation, eg: newborn skeletons - Lamellar bone: mature bone, fibrils arranged in parallel ways. Bone properties - Has both hard and light properties - High tensile and compressive strength - Large amount of elasticity - Continually modifying, reshaping and remodelling - Most osseous tissue (60-70%), organic material (type 1 collagen)(20-30%) and water (10%) - Cortical bone aka compact bone. This is the outer layer of the bone. Osteons in this allow the bone to withstand the loads. - Cancellous (trabecular) aka spongy bone. Contains trabeculae, they have little ridges in response to strain and loading. - Bone isn\'t as stiff as glass or metal, therefore will have a lower yield point on the stress/strain scale. - The behaviour of the bone depends on the direction of the applied load (anisotropic) - The behaviour of bone will also depend on the rate of the loading. When loaded quickly, it has a greater load capacity than when loaded slowly. - Bone is viscoelastic. - Bone can change due to the effects of training. - Forces around the hip can be up to 6x BW - Stress fractures is a result of an accumulation in damage and the body can\'t keep up with remodelling to prevent injury. - Fractures may be produced by single load that exceeds ultimate strength or repeated application of lower magnitude loads [STRESS FRACTURE MODEL ] Cortical Bone - Very strong - Cannot stand much strain or deformation - Stronger and stiffer - Strain rate: walking 0.1%/s, jogging 3%/s, fast running 13%/s Cancellous Bone - Good at withstanding bending loads - Cannot withstand much stress/compression loads Trabecular Bone - Fibres run along the axis of the trabecular - This part of the bone can absorb energy and distribute stress - High turnover rate - Will remodel alone the lines of stress - Not as strong as cortical bone. - Can decline over time, linked to osteoporosis - bone mass peaks about 30 years. - Osteoporosis bone has a very small stress limit and yield point. Doesn\'t effect it\'s elastic properties though. Tensile Loads - Ligaments and tendons attach to bones and this causes the tensile forces to pull on the bones. - Tensile forces can lead to the develop of apophyses, which is the thickening of bone at the insertion points of very active muscles. These growths are know as a process, tubercle or tuberosity. - Failure of bone usually occurs at the site of muscle-tendon or ligament insertion. This is when a portion of the bone tears away, aka avulsion fracture. Shear Loads - Bones are very weak when exposed to this - Common injuries seen in kids is a distal femoral ephysis - In adults, they are more likely to shatter their femoral condyle in response to shear loads Bending Loads - Caused by multiple forces on the bone. Geometry - Size and shape of the bone affects mechanical properties - Load to failure and stiffness are proportional to the CSA of bone, ie: the larger the bone = stronger and stiffer - Greater distribution of bone around neutral axis, the stronger and stiffer the bone. Cartilage Enhances stability and function of a joint by: - Reducing friction - Transmitting compressive forces across a joint - Redistributes contact stresses over larger area - Provides protection to underlying bone. - Avascular substance: has no blood supply or nerves. - Nourished by fluid within a joint - Chondrytes surround by matrix of collagen and proteoglycans (this gives it it\'s stiffness and it\'s strength) - The mechanical behaviour is affected by fluid flow. Low level of permeability. Nutrition of Articular Cartilage - Cause it\'s avascular, nourishment is derived from flow of fluid - Fluid flow is dependent on loading - Cartilage health dependent on alternating cycles of moderate compressive forces - Has limited capacity for repair and regeneration - Damaged by fatigue wear from low load, high rep forces. **WEEK 6** [Lecture 1: Neuromuscular Control ] ***ULO\'s*** - To understand differences between motor learning and motor control - Understand how the neuromuscular system adapts to training - Understand the effect of pain and injury on motor control - Understand how modes of training can affect motor control - Understand methods used to study motor control Lecture Notes - Neuromuscular control: the control of human movement is controlled by a complex interaction between the neural and muscle systems - Motor learning: is the adaptation of control of movement that occurs with task rehearsal - Motor control: execution of learnt patterns of movement and motor control - Neuromuscular adaptations is a develop of a pattern of repeated movements resulting in more skilled movement. This leads to decreased amplitude and duration of muscle activity, decreased muscle co-activation and less variability of movement and muscle activation patterns. - Humans aren\'t good at the crawling/creeping pattern. - High variability during movement is at the beginning of learning new tasks and results in increases in errors executing movements. As movements are practiced, this variability decreases and the movement becomes more accurate and \'patterned\'. - Eg: in highly trained cyclists, they had lower muscle activation and contraction during cycling output compared to non trained cyclists. - Some variability in movement is a good thing, as it can help reduce the risk of injury due to repetitive loading patterns. - We have 2 types of variability, there is gross muscle mechanics and coordination variability, ie: how you coordinate movement between segments. Increased variability between coordination mechanics is a good sign that your movement is adaptable. Ie: it\'s good to load your knee joint differently every time to help prevent injury. - Some variability is lost as skill is developed, but once we are more highly skilled, we end up with high coordination variability again and the skill is adaptable. - Cross training: short term motor learning studies provide strong evidence that there\'s interference in acquisition of a skill when another task is practiced in sequence within short interim periods (\< 6hrs). Minimum of a 4hr break is ideal, however 6hrs is much preferred. - If you practice one task immediately after the other or a very small break, it takes away some of the learning and retention of the initial task. - Initial performance gains in strength training are initially due to neuromuscular adaptations before hypertrophy occurs. - Neuromuscular control and pain: those with pain have exhibited altered neuromuscular control in comparison to healthy individuals - Lower back pain is now as common as getting the cold. There is research looking into how to reduce it across the population. - Experimental pain induces changes in neuromuscular control - EMG can look at the relationship between different muscles as a phase diagram. This is frequently used in gait analysis **Answering the ULO\'s** *To understand differences between motor learning and motor control* - Motor learning: this is the study of the processes involved in developing the precise execution of a skill and occurs through rehearsal and practice of said skill. Improvement of said skill falls into skill acquisition as opposed to motor learning. - Motor control: this is how we control learnt movements. Understanding the behavioural and the neurophysiological processes involved. Looking how we coordinate and control our bodies to be successful in the execution of the chosen movement. *Understand how the neuromuscular system adapts to training* - Neuromuscular adaptations occur as a result of repeated and practiced movement over time. This leads to decreased amplitude and duration of muscle activity, decreased muscle co-activation and less variability of movement and muscle activation patterns. - Having high movement variability at the initial stage of learning a movement is a good thing, as it allows for the body to work through movement errors and become more refined in correct technique of movement. - As the neuromuscular system adapts, there is less EMG amplitude and less muscle co activation. There is less variability in muscle activity as the movement is more correct. Ie: the cyclist study. - Initial performance gains in RT is due to neuromuscular adaptations. - Cycling before running did have some effect on triathlete performance. Gait cycle was studied pre cycle and then looking after, there was less activation however the same motor pattern occurred - RT and neuromuscular control: there\'s initial performance gains due to neural factors, not so much muscular changes. This is due to motor unit recruitment and recruitment synchronisation. *Understand the effect of pain and injury on motor control* - Pain will alter the neuromuscular control of movement. - Lower back pain is as common as getting a cold now. It\'s a burden across gen pop. - There was reduced ROM in the upper lumbar region of dancers when performing basic tasks with LBP within the transverse plane. - In a study that induced pain in their subjects, it had a pain and pain free group, in these methods, there was change in the muscle activity patterns. The use of hypertonic saline induced pain and showed an increase in EMG activity. *Understand how modes of training can affect motor control* - How much a movement is practiced and how much interruption there is in that practice will influence motor control. *Understand methods used to study motor control* - EMG activation patterns using phase diagrams. Graphing the muscle activity of one muscle on one axis and another muscle on another axis, are they working together or against each other? Are they both turned on or is one on and one off? - Multidimensional scaling, which is when you graph 2 or more muscles together. Useful when you are looking at numerous graphs and muscles. This can show if there is little or high coactivity between muscles. Still EMG based. - Factor analysis: can look at numerous muscles at once. Eg given was muscles during gait cycle and the pattern of them. This is a statistical analysis and looks at the patterns emerging and the variance in movement during gait. (more on this in the Winter textbook) - Muscle activity with respect to the movement cycle. [Lecture 2: Musculoskeletal Biomechanics (Muscle) ] ***ULO\'s*** - Factors influencing force production - Have a thorough understanding of the muscle length tension relationship - Have a thorough understanding of the muscle force velocity relationship - Understand the unique role of bi-articular muscles during human movement Lecture Notes - Muscles are a major contributor to human movement - Muscle acts in a pulling force and creates motion cause it crosses one or two joints - Tension developed by muscles applies compression to joints and enhances their stability. However if there\'s too muscle tension, it may decrease stability and result in dislocation - Force is generated in the muscle along the line of action of the force and applied to a bone. This causes a rotation about the joint - The functional effect produced by a pulling muscle force is called a torque. T = force x perpendicular distance - Moment arms change during movements. It\'s affected by the distance of the muscle insertion from the axis of rotation and the angle of pull of the muscle. This may vary anatomically between people - Skeletal muscle does: production of voluntary movement, maintain posture and enhance joint stability. - Muscles may produce very small and fine or very large and powerful movement. - Groups of muscles are within compartments that are then surrounded by fascia. - Anterior compartment syndrome: this is when there is too much within the compartment and may compress on nerves, blood vessels, etc. Can be due to overdevelopment of muscles in the given area. - Sometimes these compartments are not big enough to hold all the muscles - Force generation: tendons and muscles work together to absorb or generate force. - The exact mechanical interaction depends on the force that is being applied or generated, the speed of the muscle action and the slack in the tendon. - Hill\'s Muscle Model: 1. Contractile component: muscle 2. Parallel elastic component: surrounding connective tissue 3. Series elastic component: tendon - Phases of Hill\'s model \>\> written below Factors Influencing Force Generation 1. Muscle morphology 2. Length tension relationship 3. Force velocity relationship 4. Uni or bi articular muscle 5. Muscle fibre differentiation 6. Recruitment of motor units 7. Muscle cross sectional area 8. Temperature Length Tenson Relationship - Represents the static capability of a muscle and indicates the force that muscle can exert at different lengths - Muscle force varies in proportion to the amount of overlap between actin and myosin filaments. - Translating to an angle torque relationship is confounded by three factors: 1. Movement of most body segments is controlled by groups of muscles rather than a single muscle 2. Bi-articular muscles have length tension relationships different to uni-articular muscles 3. Change in instantaneous axis of rotation at a given joint. - Shape of the angle torque relationship varies amongst muscles Sport Performance Implications - By applying a quick stretch to muscle while it\'s contracting an additional force can be generated. This the stretch shortening cycle - Negative work: while being stretched, the muscle is lengthening and therefore, negative work Is being performed and energy is being absorbed. This is an eccentric contraction. - Tendon compliance and muscle flexibility affects this. Complaint tendons reduces your risk of damage but also increases the time it takes to produce tension. - Aging increases muscular stiffness and increases risk of injury. This will affect the compliance of our systems. Effects of stretching - Increases flexibility - Maintains and augments ROM - Increases the elasticity and length of the musculotendinous units - Increases ability to store energy. Force Velocity Relationship - Ability to produce max tension in a muscle is affected by the velocity of the contraction - The faster the movement is, the harder it is to produced max force - More stretched and slower movements allows for a better max force production - Therefore, greatest tensions are achieved when being actively stretched under load. Reasons for Force Velocity Relationship - Resistance due to viscous damping (drag within a muscle) - Resistive force increases with increasing shortening velocity, thus, in concentric contraction, the viscous damping decreases the net force output by muscle - In negative shortening velocities (ie: lengthening velocities during eccentric contraction) the viscous damping force increases the force required to stretch the muscle. - During changes in length of the muscle the cross bridges are periodically detached and reformed - Cross bridge recycling occurs with greater frequency with increasing speed of concentric or eccentric contraction - In the case of concentric contraction, this results in a smaller force with increasing velocity of shortening - In the case of eccentric contraction, greater force is required to stretch and break the cross bridge bonds with increasing lengthening velocity Muscle power output - Power = force x velocity - Power is the rate that work can be performed, important in high performance sport. - Force decreases with increasing velocity and vice versa - There is an optimum shortening velocity that maximises power output Uni and Bi Articular Muscles - One can\'t determine the function or contribution of a muscle to a joint movement by looking at the attachment points - A muscle can move a segment at one end of its attachment or two segments at both ends of its attachment - Most muscles on cross one joint. (mono articular) - Bi articular muscles convert rotational to translational movement - They\'re efficient cause the produce motion in two joints with one contraction - Disadvantage is that they\'re incapable of shortening to extent required to produce full ROM at all joints simultaneously. - Bi articular muscles have an important role in refining coordination and re-distributing mechanical movement (**journal articles in folder**) **Answering the ULO\'s** *Factors influencing force production* - Muscles exert large forces - Muscles act by creating a pull force due to cross one or two joints. It develops tension forces which acts to supress joints and works to enhance stability. - Some forces can work to creating pulling forces, causing the muscle to stretch past its limit and can result in something like a dislocation and make the muscle unstable. - The function effect is a torque, ie: moment of force. T = force x perpendicular distance. - Moment arm changes during movement, excluding isometric contraction, it is affected by the angle of the pull of the muscle, the distance of the muscle insertion from the axis of origin - Tendons and muscles work together to absorb or generate tension in the system = force production. - The exact mechanical interaction depends on the force that is being applied or generated, the speed of the muscle action and the slack in the tendon. In a relaxed state, tendon fibres are all wavy. When When under load, the straighten out and tighten up. - Factors influencing force generation: muscle morphology, Length tension relationship, Force velocity relationship, Uni or bi articular muscle, Muscle fibre differentiation, Recruitment of motor units, Muscle cross sectional area and Temperature *Have a thorough understanding of the muscle length tension relationship* - Hill\'s Muscle Model has 3 parts when it comes to the length tension relationship:\ 1. Contractile Component: muscle\ 2. Parallel Elastic Component: surrounding connective tissue\ 3. Series Elastic Component: tendon - Phase 1: when a muscle first begins to develop tension through the contractile component of the muscle (CC), the force increases nonlinearly over time. That\'s because the passive elastic components in the connective tissue and the series elastic component stretch and absorb some of the force. - Phase 2: after the elastic components are stretched, the tension that the muscle exerts on the bone increases linearly over time until max force is achieved. The tension that the muscle is exerting through the tendon is increasing. - The time to achieve max force and the magnitude of the force vary with a change in joint position. How slack the tendon is will affect this. If a tendon is slack, the max force occurs later and vice versa. - Tension in a muscle also varies in accordance with it\'s length. Muscle force varies in proportion to the amount of overlap between the actin and myosin filaments. - (more notes above) - Variations in muscle force can be influenced by torque as well. - The shape of the angle torque relationship varies between muscles. Eg: ascending pattern in the knee flexors and adductors, descending in the hip abductors and intermediate in the elbow and knee flexors and extensors. This is the optimal point in generating the most amount of torque. - Applying a quick stretch to the muscle whilst it\'s contraction provides additional force that can be generated. *Have a thorough understanding of the muscle force velocity relationship* - Increases in force less velocity and vice versa. - Greater force output is done when actively stretching the muscle and moving slower under load. Ie: negative work - Resistance due to viscous damping and this will decreases the net force output during concentric contraction and increase the net force output during eccentric contraction. - Power = force x velocity - Positive work = concentric contraction, negative work = eccentric contraction - There is always an optimal level of power production needed for different muscles. *Understand the unique role of bi-articular muscles during human movement* - One cannot determine the function or contribution of a muscle to a joint movement solely by looking at its attachment sites - Most muscles cross one joint. May be mono or bi articular muscles. - Bi articular muscles can covert rotation movement to translational movement. - (more notes above) **WEEK 7** [Lecture 1: Musculoskeletal Mechanics (Ligament and Tendon]) ***ULO\'s*** - Describe the mechanical properties of a ligament and tendon - Explain how ligament and tendon responds to normal and abnormal loading patterns - Describe methods for measuring ligament and tendon mechanics - Understand how concepts of biological tissue biomechanics can be used to examine musculoskeletal loading. **Class notes** - Tendons and ligaments are dense connective tissue containing 70% water, 25% collagen fibres and 5% elastin. - Tendons: parallel collagen fibre arrangement, carry high tensile loads and are stiff but have minimal resistance to compression and shear loads. - Ligaments: nearly parallel collagen fibre arrangement, can carry high tensile loads and are less stiff and slightly weaker than tendons. - Both have similar microarchitecture. - Factors influencing biomechanical function: aging, pregnancy, immobilisation, diabetes, haemodialysis and NSAIDs. Ligaments - Role of ligaments is to provide connect from bone to bone. These are important to look at mechanical and it is the site of transmitting energy to the bone from the muscle. - Ligaments can stretch about 8-10% before failure. Bone can only stretch up to 1% - Increase mechanical stability of joints - Guide joint motion and prevent excessive motion - They have viscoelastic behaviour and control the dissipation of energy. - Ligaments respond to loads by becoming stronger and stiffer over time, demonstrating both a time-dependent and non linear stress-strain response. - The ligament to bone attachment reduces the mechanical loading transmitted by the ligament to the bone. - Yield point is about 3% of strain, failure/breaking point is 8% - Collagen fibres in a ligament are arranged so that it handles both tensile and shear loads, however ligaments are best suited for tensile loading. Ligament and Injury - At the end of the ROM for every joint, a ligament usually tightens up to terminate the motion - Ligaments provide passive restraint and transfer loads to the bone (**like a seat belt**) - A ligament can be subjected to extreme stress and damage while overloaded when performing the role of restricting abnormal motion. - Injury can be a result to overloaded movements, repetitive poor loading over time, excessive stretching of the ligament or due to an unstable joint. - Immobilisation changes the biomechanical behaviour of a ligament. Becomes more elastic but doesn\'t keep the same level of stiffness. It\'s yield point is lower than a healthy ligament. - Tensile injuries to a ligament - Common in adults - Tend to occur in high speed conditions - Has a 1-3 grading system Avulsion Injury - Tensile load causing a bone fracture - More common in kids due to growing bones that they\'re bones are softer - This is when a piece of bone breaks off. Immobilisation - Causes changes in biomechanical behaviour in ligaments - Becomes more elastic but doesn\'t retain stiffness and then has a lower gradient on the load/elongation curve. It\'s yield and failure points occur at lower loads. Knee ligaments - Most common ligament injury - The ACL and PCL make the four bar linkage system for the knee joint. - ![](media/image10.png)During extension and flexion, the ligaments pivot relative to each other but still keep tension. They keep the bones rotating over each other. - The knee joint doesn\'t have a set centre of rotation, it has an instantaneous centre of rotation that moves and stays with the cross over point of the ACL and PCL - The shape and tension of the ACL changes from extension to 90 degrees of flexion. - When the knee is extended the MCL is taught on both sides to resist valgus and tibial rotation, however when the knee flexes, the posterior side relaxes and the anterior side stays taut. - These ligaments have a key role in keep the menisci in place within the knee to sustain shock absorption. ACL Rupture Common mechanisms - Valgus loading in combo with external tibial rotation - Knee hyperextension with internal tibial rotation - Anterior drawer mechanism. When the tibia is forced forwards relative to the body and you have to decelerate rapidly. - ![](media/image12.jpeg)When loaded at a fast 66% of failure was ligamentous (loading in the ligament). When loaded at a slow rate, 57% was due to tibia avulsion. Tendons - Attach muscle to bone - Transmit tensile loads to bones to let us move - Help us maintain posture. - Large collagen content and are quite strong, relatively stiff. - Can act as a dynamic restraint. They have an optimum distance between the muscle belly to where it inserts on the bone. - Failure point is 8% - Have an elastis modulus of about 800 mega pascals to 2 gigga pascals. - Stress strain curve \>\>\> Achilles Tendon - Its ultimate strength is about 350N in cadavers, so in a living person, it is expected to be more. - Tendons are also responsive to hormonal changes, the use of the contraceptive pill and pregnancy change the strength of it. Pregnancy reduces stiffness - Tendons respond to eccentric training. - Hysteresis: 2.5-10%. The amount of energy between when it\'s loaded and stretched and then when it releases the energy and returns to its resting. Its ability to store energy is limited except when loaded in large forces. - Has high tensile strength Tendon to Bone attachment 1. End of the tendon (softer) 2. The collagen fibres intermesh with the fibrocartilage 3. The fibrocartilage gradually becomes mineralised fibrocartilage (more bone like) 4. Merges into cortical bone. - Going from soft tissue to hard tissue. - Can change and adapt due to SAID principle. - Max load to failure image: loss of almost 40% of load ability. There is a high rate of reinjury following ACL ruptures. - Energy stored to failure: similar thing. Lower limb strain injury - Common in many sports. - Calf injury is common in running and sprinting based sports. Thoughts around it is that it\'s due to acceleration and rapid breaking - In 2001, a gastroc strain was caught on camera in a cricket test match. This was reviewed and noted that the gastroc was close to max length when this happened, but it occurred when the muscle tendon was at constant length. Concurred that it happened when it went from eccentric to isometric loading. \*rest of this lecture was talking about journal article examples of calf and hamstring strain. Probs should go back and look at them. - In runners, they found neuromuscular deficits in the hip and calf complex, leading to increased risk of injury. - Hamstring strain injuries are common in running sports, especially sprinters. 2 potential scenarios for injury:\ 1. stretching type of injury, common affects semimembranosus. Likely to occur during kicking or picking up a ball from the ground at full speed\ 2. high speed running, affecting the long head of the biceps femoris. Common in AFL. - Hammy strains are most likely to occur in eccentric actions in the late swing phase. Can occur in the late stance phase if running with a forward trunk lean. **Answering the ULO\'s** *Describe the mechanical properties of a ligament and tendon* - Tendons and ligaments are dense connective tissue containing 70% water, 25% collagen fibres and 5% elastin. - Tendons: parallel collagen fibre arrangement, carry high tensile loads and are stiff but have minimal resistance to compression and shear loads. - Ligaments: nearly parallel collagen fibre arrangement, can carry high tensile loads and are less stiff and slightly weaker than tendons. - Both have similar microarchitecture. - Factors influencing biomechanical function: aging, pregnancy, immobilisation (more related to sports injury topics), diabetes, haemodialysis and NSAIDs. *Explain how ligament and tendon responds to normal and abnormal loading patterns* NORMAL ABNORMAL *Describe methods for measuring ligament and tendon mechanics* - Using stress strain curves - The mechanical loading device (shouldn\'t be used anymore as it required literal tendon or ligament samples) - ACL testing, looking at joint displacement. - Human cadaver testing *Understand how concepts of biological tissue biomechanics can be used to examine musculoskeletal loading.* [Lecture 2: Mechanical Problem Solving Methods ] ***ULO\'s*** - Explain the three different movement description methods (phases, deterministic models and free body diagrams) - Understand how to design a free body diagram - Have awareness of some more advance problem solving methods in biomechanics. Class Notes - Movement phases: sequential approach to problem solving. More qualitative or semi quantitative. - Mechanical approach: deterministic model. Concept map looking at the primary performance factor and then breaks it down into further sub categories. - Mechanical approach: Free Body Diagram. The aim is to reduce the complexity of a mechanical analysis. It defines the extent of the analysis and identifies the significant forces involved in the action.\ usually uses a version of a stick figure along a set of coordinates, with the forces added as arrows. The stick figure indicates the system involved in the analysis. The forces are magnitude, direction, line of action and point of application. [Types of Forces on the FBD ] *External*: - weight: combo of mass and gravity (mass x gravity), the vector direction is always down towards earth, originates from the body\'s COG and that is determined through an analysis of body segments. Centre of gravity is often used by looking at ones hip position, otherwise a 3D set up would be needed. - ground reaction force: reaction force from interaction with the ground. Derived from Newton\'s 3rd law (action-reaction), usually measured by a force platform. A normal force is perpendicular to the surface. - fluid resistance: both human and projectile motion can be greatly affected by this. FR can be split into lift and drag components. Can occur in swimming, cycling and sprinting. You need to account for air or water resistance. *Internal*: - joint reaction force: net force generated by bone on bone contact between adjacent segments when loaded. Loads caused contact forces from muscle, ligaments and bones that are exerted across a joint. These forces are calculated as they difficult to measure, inverse dynamics are used. They often act solely on a joint centre so rarely contribute meaningfully to joint torque. Harder to measure. Need to use inverse measures. - muscle force - IAP: transmits forces from the muscles encasing the IA cavity to the supporting structures f the trunk. Muscles include the TA, RA, obliques and diaphragm and pelvic floor muscles. Voluntary pressurisation is often referred to as the Valsalva manoeuvre. Need to close the epiglottis and activate the trunk muscles. \*elastic and inertial forces may also be included but isn\'t covered in this unit. FBD - Statics - A body or object at rest or when moving at a constant velocity - Acceleration = 0 - Sum of all forces = 0 - X direction: medial - lateral - Y direction: anterior - posterior - Z direction: vertical \*this FBD had maths from last year in it Inverse Dynamics - Modelling technique - Kinematic data (3D motional analysis) \> kinematic model \> dynamic model - Kinetic data (comes from a force platform or EMG) \> dynamic model - Anthropometric data \> anthropometric model \> dynamic model. Need to add height, weight, leg length, etc. - Uses external forces to estimate internal ones. Advance techniques - More invasive that we don\'t learn about. - Skin pin markers. Surgical placed into the underlying bone ACL Mechanics: Strain Gauge - Inserting a strain gauge. Used to measure bone loads across the joint the ACL itself. **ANSWERING ULO\'S** *Explain the three different movement description methods (phases, deterministic models and free body diagrams)* Phases: - Sequential approach: more qualitative or semi quantitative. Breaks things into movement phases and sub phases. Also looking at points of interest within the movement. Deterministic Models: - Mechanical approach: concept map looking at the primary performance factor and then breaking it down into further concepts of the smaller things making up the primary movement. FBD\'s: reduces the complexity of a mechanical analysis. Defines the extent of the analysis and identifies the significant forces involved. *Understand how to design a free body diagram* - Uses a stick figure of the system that we\'re looking at. - Coordinates and forces are added. (lower leg example). Forces imposed on the system by it\'s surroundings. - Force magnitude can be added and is defined by the size of the arrow and the direction that it is going in. - (forces added listed above) *Have awareness of some more advance problem solving methods in biomechanics.* - Inverse dynamics (listed above) - More invasive techniques. In vivo techniques. Surgical implantation of equipment. Implantable strain sensors and virtual fibre elongation. - Bone pin markers. Reflective markers are inserted into the underlying bone. Is very accurate to get data about movement at the bone level. **WEEK 8** [Lecture 1: Gait Kinematics ] ***ULO\'s*** - To understand and recognise the kinematics of normal healthy walking - Understand typical gait terms - Understand the 6 determinants of gait ***Class notes*** - Gait: pattern of movement that allows animal during locomotion to move across a solid substrate. - You can analysis the gait of humans and animals. - Type of locomotion: crawling, walking, running, hopping and skipping. Gait cycle - In lamens terms, 2 steps. - There is initial contact and toe off. - For running, the key event may be toe off. - The time interval between two successive occurrences of the same event of locomotion. Ie: walking a few steps. - Key phases of the gait cycle: stance and ends with toe off, then the swing phase which is the toe off to the initial contact of the opposite foot - 60% stance and 40% swing phase - We then have sub phases and events - GO BACK OVER THE INDIVIDUAL SUB PHASES. - The stance phase has 4 sub phases - The swing phase has 3 sub phases. - Heel strike = initial contact. Certain conditions, eg: cerebral palsy may start on toes. - Stance and swing % begins to change as our speed/velocity increases and there is more time spent in a swing phase. - 1 stride = 2 steps. - Walk 1.5m/s = 60% stance, 40% swing - Race walk 3m/s = 50/50 - Run 5.m/s = 30% stance, 70% swing - Spring 9m/s = 20% stance, 80% swing - Walking has a period of double support = 2 foot contact with the ground. Running doesn\'t have this. There is a double support phase that makes up 15% of the gait cycle. ![](media/image14.png)![](media/image16.png)Gait Terms - Step length: whichever leg is leading in the swing phase. - Stride length: - Step time: - Stride time: distance in between 2 feet - Cadence: frequency - Stride width (walking base): - Foot angle (toe out): - Stride time (s) = 1/stride frequency (Hz) - Ipsilateral: term used for the limb being studied - Contralateral: term used to describe the mechanics of the opposite limb Gait Velocity Stride velocity (m/s) = stride length (m)/ stride time (s)\ = stride length (m) x stride frequency (Hz) [KEY KINEMATICS ] Initial Contact (the image had the right foot leading, for context) - Trunk: behind leading foot, crosses midline toward the stance leg, right pelvis forward - Hip: flexed - Knee: extended, starting to flex - Ankle: neutral - Foot: supinated - Contact to the ground through the heel results in a most vertical force vector acting through the heel and ankle. Not quite plantar flexed or supinated at this point. The knee will be extended and the hip will be flexed. Loading Response - Start of the double support period - Body has travelled over the supporting leg and the force vector is now going through the heel, passing through the knee but is still in front of the pelvis. The foot is starting to pronate and tibial internal rotation is happening. There will be some lateral trunk shift towards the stance leg to help balance and stabilise the body - Trunk: lowest vertical position, moving laterally towards the stance leg - Hips: beginning to extend - Knee: flexing - Ankle: plantar flexing - Foot: pronation (eversion) and tibial internal rotation. Foot Flat (Contralateral Toe Off) - End of first double support period. The contralateral limb is at toe off and the stance limb now has the pelvis more over it, the foot is flat on the ground and the ankle is dorsi flexing cause the tibia is moving over the foot. The force vector is passing behind the knee and just in front of the pelvis. - Trunk: begins to gain height, right pelvis coming back to neutral - Hip: extending (25 degrees flexion) - Knee: flexing - Ankle: dorsiflexing as tibia moves over foot - Foot: pronation (eversion) and tibial internal rotation peak Mid Stance - The weight has shifted forwards to the middle of the foot. The force vector is now passing through the middle of the foot and through the knee and stance leg. We only have a vertical force at this point in time, no horizontal force here. The tibia has moved into external rotation and the tibia is moving forward over the foot and cause the knee has reached peak flexion, it will start to extend. This is when centre of gravity is highest. - Trunk: trunk reaches highest point, peak lateral motion of trunk, pelvis passes through neutral - Hip: extending - Knee: reaches peak knee flexion and begins extension - Ankle: dorsiflexing as tibia moves over foot - Foot: supination (inversion) and external rotation of tibia. Terminal Stance - Now have second double support occurring - Period from ipsilateral heel off to contralateral foot contact - also called \"push off\" - When the heel leaves the ground this is really when propulsion and horizontal forces occur. You\'re about to shift your body weight to the other limb - Trunk: moving to the opposite side - Hip: reaches its most extended position - Knee: moving back into flexion - Ankle: plantarflexing - Foot: reaches maximal supination Initial Swing - Period from toe off through to feet adjacent - The force vector is passing through the very last point of the toe on the original staring leg and in the direction of forwards and upwards, will pass through the proximal end point of the tibia, behind the knee and behind the hip. - On the left side (all the below happens). - Trunk: trunk moving through neutral toward the new (left) supporting foot, trunk gains height - Hip: flexing - Knee: flexing (mainly due to flexion of hip - pendulum) - Ankle: moves from plantarflexion to neutral or dorsiflexed position - Foot: slightly supinated Terminal Swing (late swing) - Period from feet adjacent through to initial foot contact provided toe clearance has occurred, ankle is pretty neutral. - Trunk: moves from maximal displacement on left side back toward midline and trunk loses height - Hip: flexion (rate of flexion decreasing) - Knee: rapid knee extension (mostly passive) - Ankle: once toe clearance achieved ankle position not as important - Foot: remains in supination. Sagittal plane kinematics - A hip angle is the thigh segment angle - the trunk segment angle - Trunk angle segment from the greater trochanter of the femur bone through to the iliac crest. - Thigh segment: greater trochanter to the femoral condyle - Positive hip angle = flexion - Negative hip angle = extension - For the ankle, you need to measure shank - foot + 90 degrees. ![](media/image18.jpeg)Sagittal plane motion What\'s normal? - Peak hip extension occurs in terminal stance of the gait cycle - Data collected for men showing data around normal amounts of flexion and extension. - Left graph: Flexion \> extension \> flexion, peak hip extension occurs during terminal stance - Mid graph: flexion \> extension \> flexion \> extension. The knee never reaches full extension, first peak flexion occurs mid stance and is most extended just before terminal swing - Right graph: PF \> DF \> PF \> DF \> Neutral \> DF: there is slight DF at the start, PF just past early swing and then goes back to DF for ground clearance. ![](media/image20.jpeg) Frontal Plane Kinematics - We don\'t use supination and pronation, inversion and eversion are used. - Rear foot = shank - calcaneus - Positive rear foot = inversion - Negative rear foot = eversion Sub-Talar Joint Motion - Normal range of motion, 5 degrees of pronation and 4 degrees of supination. Determinates of gait - There are 6 - There aim to minimise the excursion of COM 1. Pelvic rotation: hip and pelvis movement. There is rise and fall happening in the vertical direction, this happens as more weight shifts over the stance limb. When looking side on, you can see a rise and fall happening when base shifts over stance limb. 2. Pelvic obliquity: pelvis will tip up and down during the gait cycle. Tips in the frontal plane, it will move downward during swing and up during stance. Tries to help reduce vertical movement in COM. We want a little bit of movement to help dissipate forces and reduce back load. You want this movement, otherwise you have shit gait. 3. Stance phase knee flexion: adjusting the length of leg during the stance phase to maintain hip height. Works to keep the hip at a stable height. Occurs at Mid Stance. 4. Ankle mechanism: lengthening of the leg at initial contact and toe off. Tries to lengthen the leg, flattens the leg, to help keep the hip height stable. 5. Foot mechanism: external rotation of the leg and supination of the foot lengthening the leg at toe off. ER happens at toe off at the same time that supination happens. 6. Lateral displacement/genu valgum: we don\'t walk as robots. We have slight valgus at the knee to help reduce side to side movement as we walk. Typical Values (normal walking for adults 20-59 years) - 2.2 m/s, about 8kms per hour - Cadence: 112-120 steps per minute - Stride length: 1/22 - 1.53m - Velocity: 1.20 - 1.45 m/s - Double ST: 20-25% Walking vs running - No double limb support phase - Running has 2 float periods - Stance swing ratio changes - Increased hip and knee flexion and increased plantar flexion in running to increase propulsion Running - Stance 30% - Swing 70% - Swing sub phases: early float, mid swing, late float - Recovery phase: from toe off through to knee flexion and knee alignment - Drive phase: drives forward, through to initial contact. Normal Rearfoot Motion (go back over this too) - Occurs slightly on the lateral side of the heel - Foot in neutral alignment and then begins to move in pronation which occurs for about 70% of the ground contact phase, with max pronation occurring around 40% of the phase. - Then supination starts, the heel rotates inwards ***ULO Answers*** *What are the kinematics of normal healthy walking?* - Crawling, walking, running, hopping and skipping. - 2 steps are a gait cycle. Initial contact off one foot, through to the next foot and then returning to the beginning foot. - Stance phase is typically 60% and swing phase is 40% *What are typical gait terms?* There are new and classic terms, as depicted in the picture above: New: 1. Initial contact 2. Loading response 3. Mid stance 4. Terminal stance 5. Pre swing 6. Initial swing 7. Mid swing 8. Terminal swing Classic 1. Heel strike 2. Foot flat 3. Midstance 4. Heel off 5. Toe off 6. Midswing 7. Heel strike Other terms (definitions above) - Step length - Stride length - Step length - Step time - Stride time - Cadence - Stride width - Foot angle. *What are the 6 determinants of gait?* 1. Pelvic rotation 2. Pelvic obliquity 3. Stance phase knee flexion. 4. Ankle mechanism 5. Foot mechanism 6. Lateral displacement Lecture 2: Gait Kinetics ![](media/image22.jpeg)***ULO\'s*** - Understand and recognise the kinetics of normal healthy walking - Understand the difference between external and internal joint moments - Recognise the kinetic differences between walking and running - Understand the muscular roles for support, braking and propulsion ***Class notes*** - Gait: stance phase and swing phase. New terms and old terms. Sub phases - Initial contact force creates the positive vertical force and a negative horizontal force. When added together, is a force that acts backwards but upwards. - At mid stance, there\'s a vertical force acting upwards, horizontal force is = 0. - At toe off, there\'s positive vertical force acting upwards through the body and positive horizontal force as it\'s acting in the way you\'re travelling. [Ground reaction forces ] Vertical - 2 hill shape for constant velocity walking and the 2 hills are equal in magnitude. - Double support phase on a diagram indicates it\'s walking not running. There will be a cross over. - F1: upward deceleration of COG (peak arrest). Aka weight acceptance. Rate of change in the force/weight in time - F2: COG moving over the stance limb (mid stance). Push off rate. - F3: upward acceleration (propulsion) of the COG (peak thrust) Horizontal (anterior posterior) - Dip and hill shape - F4: peak braking (arrest) - F5: Mid support (Fy = 0 BW due to change of direction) - F6: Peak propulsion (thrust) ![](media/image24.jpeg) In early stance phase - In normal gait, there\'s a force vector acting slightly behind the knee - Quad contraction is important in early stance phase - During clinical gait analysis, there\'s 2 abnormal things that may be detected: 1. Anterior trunk bending: when the force vector is acting in front of the knee. Occurs when trunk flexion is occurring throughout the whole gait cycle and can be a result of poor quad strength. 2. Posterior trunk bending: the force vector passes behind the knee and hip. This occurs when there is trunk extension at the line of heel contact and is due to poor hip extensor strength. - Ground reaction force patterns can change with increasing velocity. - The vertical force curve changes the most, the horizontal force curve doesn\'t change that much but the magnitude and time of each may change. - Running patterns: the impact peak is smaller than the active peak - Running downhill: impact peak become larger and active peak gets smaller. For the horizontal forces: breaking peak becomes more dominant than propulsive. - Uphill running: more pronounced active peak and greater propulsive forces. ![](media/image26.jpeg) Medial Lateral Direction (Fx) - Small dip and wide hill shape - F7: max supination (lateral direction) - F8: max pronation (medial direction) - Medial directed force is positive and lateral is negative for the right limb and opposite for left limb - Less sensitive to changes in force with walking speed. GRF Variability - Makes it hard to be precise with measurements - Nothing to do with equipment, it\'s about movement of the person - This is why the Fx direction isn\'t always analysed. \*moment here is looking at the torques occurring within the body Initial Contact - Hip: extension moment (generating power) - Knee: flexion moment (short period of power generation) - Ankle: neutral - GFR is acting upwards through the knee and ankle joint. There\'s a neutral ankle position, no moment occurring here. At the knee, there\'s a flexion moment and at the hip there\'s an extension moment. Loading Response - ![](media/image28.jpeg)The GRF vector is acting through the middle of knee and slightly in front of the femur. At the ankle, it\'s moving from negative to positive, the knee is still negative and the hip is still positive. The ankle is the only thing that\'s changed. - Hip: extension moment (generating power) - Knee: flexion moment (short period of power generation) - Ankle: posterior force vector = external plantarflexion moment Mid stance - The force vector is behind the knee but in line with the hip. There is some initial power absorption replacing generation in the knee. - Hip: extension moment decreasing - Knee: posterior force vector = external knee flexion moment, initial power absorption replaced by generation - Ankle: increasing plantarflexion moment, absorbing power. Terminal Stance - The resultant force vector is behind the knee and hip. Generation stage at the ankle. The hip is now in a negative moment. - Hip: flexion moment (passive tension), mostly power absorption but moving towards generation. - Knee: flexion moment, moving to extension moment to limit rate of knee flexion (absorption) - Ankle: high plantarflexion moment (generation) Initial Swing - Hip: flexion moment and power generation - Knee: flexion due to pendulum = knee extension moment and power absorption - Ankle: decreasing moment and power Terminal Swing - No GFR occurring here. - Hip: increasing extension moment - Knee: increasing flexion moment and power absorption - Ankle: neutral Joint Power Patterns - Corresponds to the gait cycle - Important in clinical gait analysis. Looing at knee joint power patterns, 5 points to analyse. The hip joint normally has 3 points assessed. The ankle only has 2 points analysed. - Eg used was a female case study which is rare. Braking Phase - H1: hip extensor power generation (concentric). From glute max and hamstrings - K1: knee joint power absorption (eccentric). From quads - K2: knee extensor power generation (concentric). From quads - A1: ankle power absorption (eccentric). From triceps surae (gastroc and soleus) Propulsion Phase - H2: hip flexor power absorption (eccentric) - A2: ankle plantarflexion power generation (concentric) - K3: knee extensor power absorption (eccentric). From rectus femoris. Swing Phase - H3: hip flexor power generation (concentric) - Knee extensor power absorption (eccentric) - Knee extensor power generation (concentric). From quads. Frontal and Transverse Plane Kinetics - The goal of locomotion is to support the body against gravity whilst moving forward in the plane of progression. - Need full 3D motion analysis, need anthropometry data for this. Using Vicon system, force platforms, EMG and inverse dynamics. - Important to get this data to support the body against gravity - Minimal motion in frontal and transverse planes. This is why there is more focus on the sagittal planes. - Hip abduction moment vs hip power: not typically looked at. H3 is more about generation. - Knee abduction movement vs knee power: power is more looked at, specially the stabilisers in the frontal plane. Looking at the stabilisation of the abductors, ITB and TFL and passive forces from ligaments to counteract the adductor stress from the upper body when the weight is passing medial to the knee. Plantar pressure - Indirectly reflect accelerations of all body parts as we walk - Will be unique to everyone. - Often look at the peak pressure in zones of the foot. - Modified Arch Index (MAI) this looks at peak pressure in the middle of the foot (zone B) equation for this is zone b/zone a + B + C and COP (centre of pressure) Excursion Index (CPI) equation for this is CPI/foot width x 100 - Hallux valgus is an issue with the big toe where the middle of it bones in. Pressure Zones - M01: Hallus - M02: lesser toes - M03: lateral forefoot - M04: medial forefoot - M05: lateral midfoot - M06: medial midfoot - M07: lateral rearfoot - M08: medial rearfoot. Muscle Activity (EMG) - Gives an overall perspective of when muscles are turned on and off - **On the slides are the different EMG for lower musculature activation** - During initial contact, the glutes, hamstrings, quads and tib anterior kick on first. - (photos in phone) - Activity of all muscles go towards propulsion and breaking during the gait cycle - The Achilles can experience up to 6-8 x BW in forces through it. Energy Source - The sources of power generation for forward propulsion provides insight on the strategy of movement - Hips are powerful extensors during the second half of swing, the knee flexors are for the first half of stance. - Movement strategy changes with increasing speed. - Total amount of power generated changes between gait modes. In walking, ankle plantar flexors dominate, in running the power generation shifts more to the hips and knees, this would increase more with sprinting. Tends to shift from distal to proximal power generation. Spine pathways in Gait - In running or walking, the hip extensors fire as the toe pushes the ground - The muscle is directly transmitted to the spine and trunk via two distinct but complementary pathways - Firing the hip extensors extends and raises the trunk in the sagittal plane. Causes of Inefficient movement - Co contractions: muscles fighting against each other. Typically occurs in something like cerebral palsy. - Isometric contractions against gravity: segments are held in isometric contraction - Generation of energy at one joint and absorption at another: one joint is making positive energy and another negative. Very similar concept to co contraction. - Jerky movements: very start and stop. The problem with this is that it has a high metabolic cost. Overview of Clinical Gait Analysis - You collect client data to identify their gait deviations and figure out what is causing them. Relevant medical data will be reviewed, plus any referring notes from other health professionals. - Most reliable way is 3D motion analysis - Come up with medical treatment, not really done by the biomechanist but data collected will help guide those decisions. ***ULO Answers*** *What are the kinetics of normal healthy walking?* - A full gait cycle has 2 strides. - In GFR, there are different forces that are important to look for in the graph. (listed above) - When walking at constant velocity, you\'ll see equal points of magnitude on the GRF scale. - During the horizontal forces, it\'s like a big dip with 3 different forces assessed (listed above) - Initial contact points = positive vertical force and a negative horizontal force, the resultant force vector acts backwards and upwards. - At mid stance, there is a vertical force acting upwards and there\'s no horizontal force which = 0, this is pure vertical force - At toe off, there is a positive horizontal vertical and horizontal force, it\'s acting upwards and forwards through the body as this is way we are travelling. - In normal gait, the force vector acts slightly behind the knee in early stance phase. Abnormalities may present as anterior trunk bending, this is normally due to poor quad strength but quad contraction is needed to oppose the torque to allow weight bearing. The other abnormality is posterior trunk bending, the force vector will pass behind the knee and hip, this will occur with trunk extension at heel contact, this is due to poor hip extensor strength. May show throughout the whole gait cycle. - GFR will change with increasing velocity - Medial forces detailed above. *What are the differences between external and internal joint moments?* - Gait cycle moments are all detailed above and at the hip, knee and ankle. - This part of the lecture didn\'t specify internal/external, so all detailed above. *What are the kinetic differences between walking and running?* Walking Running - Changes to proportion between the impact peak and active peak. The active peak is normally bigger. - Horizontal force curve won\'t change that much, just the shortening of start time and increase in magnitude of forces. - When you run downhill, the impact peak gets bigger and the active peak gets smaller. Breaking peak becomes more dominant compared to propulsive forces. When running uphill, this is opposite. *What are the muscular roles for swing, braking and propulsion?* (listed above) - Swing: H3, K4 and K5 (heavy quad contribution here) - Braking: H1, K1, K2 and A1 - Propulsion: H2, A2 and K3 **[WEEK 9]** Lecture 1: Pathological Gait **ULO\'s** - Understand functional categories of gait impairment - Understand age related changes in gait patterns - Recognise common gait impairments - Understand what is included in observational gait analysis - Understand what is included in 3D gait analysis **NOTES** [Pathological Gait: Perry (2010) Five Functional Categories of Gait Disorders] 1. Deformity: does it affect mobility? Doesn\'t permit sufficient mobility to attain normal postures and ROM, eg: PF contracture, knee flexion contracture and club foot. Increased hip flexion due to poor ankle movement. 2. Muscle weakness: disuse muscle atrophy or neurological impairment, eg: aging, motor neuron disorders (eg: Guillain-Barre syndrome). Classic sign of this dysfunction is hesitant to initiate gait action. Also muscular dystrophy and polio-something?

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