Biomechanics Lectures PDF

Biomechanics Dr. Bassem Khalifa Assistant Professor of Orthopedic and Sports Physical Therapy  Biomechanics is the study of motion and its causes in living tissues (human and animal) Provides conceptual and mathematical tools necessary for understanding how living things move and...

Biomechanics Dr. Bassem Khalifa Assistant Professor of Orthopedic and Sports Physical Therapy  Biomechanics is the study of motion and its causes in living tissues (human and animal) Provides conceptual and mathematical tools necessary for understanding how living things move and how professionals improve movement or make movement safer Provides key information on the most effective and safest movement patterns, equipment, and relevant exercises to improve human movement Physical educator or coach who is teaching movement technique and the athletic trainer Physical therapist treating an injury use biomechanics to qualitatively analyze movement  Biomechanics Biomechanics: the study of the movement of living things (systems or tissues) using the science of mechanics Mechanics: the study of motion and how forces create motion Biomechanics: study of the structure and function of biological systems by means of the methods of mechanics Study the internal and external forces acting on the human body and the effects produced by these forces Forces acting on living things can : Create motion Stimulus for growth and development Overload tissues and causing injury Orthopedic Biomechanics Ortho: perpendicular or correct "straight" and pedic ("child"): Art of Correcting and Preventing Deformities in Children Orthopedic: dealing with bone or treatment of musculoskeletal disorders Bio: Living system or tissues Mechanics: science of motion and force Force and motion in a living system Orthopedic Biomechanics: the study of motions and forces in human musculoskeletal system AREAS OF STUDY, RESEARCH AND PRACTICE Sport and Exercise Science Coaching Ergonomics: equipment design Gait & Locomotion Orthopedics - Rehabilitation (Physical &Occupational Therapy) Prosthetics and Orthotics Motor Control Computer Simulation Video Games (fifa) Biomechanics: Does it exist in more than one field? Exercise and sport biomechanics: improving athletic performance, reduction of athletic injuries Identify the risk factors for musculoskeletal injuries and design prevention program Landing strategies ACL prevention rehabilitation program Study the changes in the joint biomechanics after musculoskeletal injuries and to develop appropriate rehabilitation program Orthopedic biomechanics: Artificial limbs, joints, and orthoses to improve functional movement capacity Study of natural and artificial biological tissues Occupational biomechanics: Ergonomics and Human Factors Reduction of workplace injuries Biomechanics of other biological systems Comparative biomechanics (e.g., swimming in fish, locomotion in apes) Horse and dog racing performance Biomechanics: Does it exist in more than one field? Engineers and occupational therapists Design work tasks and assistive equipment to prevent overuse injuries related to specific jobs Design helmets to prevent head injury automobile vehicles (Calvano & Berger, 1979; Norman, 1983; Torg, 1992) Amputation, prosthetics, or artificial limbs Designed to match the mechanical properties of the missing limb (Klute Kallfelz, & Czerniecki, 2001) Prescribe rehabilitative exercises, assistive devices, or orthotics Orthotics and assistive devices Correct deformities or joint positioning Help patient function like canes or walkers  Biomechanical testing allows identifying aberrant movement patterns and altered neuromuscular strategies that are caused by musculoskeletal and neurological injuries where they cannot be captured by the standard clinical evaluation. Has clinical applications as it can contribute to the prediction of patients with a higher risk for injuries. Examine the complexity of human musculoskeletal function by studying the role of the bony segments, joint-related connective tissue structure, muscles, and the external forces applied to those structures Human motion is inherently complex, involving multiple segments (bony levers) and forces that are most often applied to two or more segments simultaneously Movement is essential to life Type of movements: 1. Translational or linear motion:  Body moves along a straight line (rectilinear) or curved line (curvilinear motion) 2. Angular or rotational motion:  Body rotates about an axis of rotation  Infinite number of axes about which a body can rotate  Most of the movement performed in the living organisms are combined of linear and angular motions: General motion  Motion of the thigh during walking :  Entire thigh moves linearly in forward-backward direction with angular rotation at the hip joint (flexion-extension)  Basketball: linear motion to the rim and rotation (spinning around itself) Human Movement Mechanics Internal mechanics Mechanical factors that produce and control movement work from inside the body Muscle contraction ligaments External mechanics Mechanical factors that produce and control movement work from outside the body Gravity Trauma Descripting the movement Vs identifying the factors that involved in production and controlling the movement  Mechanics of motion Statics Dynamics constant state of motion acceleration present Kinetics of motionless Constant velocity Kinematics Kinetics systems systems Kinematics Kinetics Kinematics and Kinetics  Kinematics: Description of the movement without regard to the forces that produced the movement Describe time, displacement, velocity, & acceleration Can be linear or angular or combined  Kinetics: studying the forces that produce or change motion Force can produce: Translational (linear) motion Angular motion Statics and Dynamics Biomechanics includes: statics & dynamics  Statics: all force acting on a body are balanced (∑F=0) The Body is in equilibrium (either the body is in motion or motionless)  Dynamics: deals with unbalanced forces (∑F≠0) Causes object to change speed or direction Excess force in one direction A turning force Principles of work, energy, & acceleration are included in the study of dynamics Kinematics: Kinematics can be assessed by: Qualitative (‘good’ or ‘bad’) by observation Quantitative (use of numbers to increase precision and objectivity of the description) Kinematic variables (Quantitative): Temporal characteristics (how long did the movement take, how fast is it going, is it speeding up or slowing down) Spatial characteristics (where is it, how far did it go, in what direction) Type of displacement (motion) Position or location in space of the displacement Direction of displacement of the segment Magnitude or displacement (describing what movement has occurred) The rate of displacement or rate of change of displacement (velocity or acceleration) Velocity (how fast has moved) Acceleration ( indicator of how quickly the velocity has changed) Linear & angular motion  Vector- quantity having both magnitude and direction Force-push or pull action You throw a ball with direction and speed Scalar- has only magnitude. Length, area, volume, mass Mass is the amount of matter a body contains. Inertia is change in motion in either speed or direction. Kinematics Temporal characteristics of kinematics (Time): Provides a measure of duration of a particular event Time in the air during jump Duration of right foot contact with ground: 450 ms Duration of a force application during injury Loading rate or force impulse Kinematics: Spatial characteristics Types of Displacement: Translatory and angular motions General motion: Both translator and Combined Translatory motion (linear displacement) Rectilinear motion: in straight line Curvilinear motion: in curved line In true translatory motion, each point on the segment moves through the same distance, at the same time, in parallel paths. Example of translatory motion: the movement of the combined forearm-hand segment as it moves forward to grasp an object Translation of a body segment rarely occurs in human motion without some concomitant rotation of that segment (even if the rotation is barely visible)  Angular or rotational motion Angular or rotational motion: movement of an object along a circular path around an AXIS. This axis is known as the axis of rotation Infinite number of axes about which a body can rotate In true rotatory motion, each point on the segment moves through the same angle, at the same time, at a constant distance from the center of rotation (CoR) True rotatory motion can occur only if the segment is prevented from translating and is forced to rotate about a fixed axis. This does not happen in human movement. Angular motion is produced when forces are applied away from the axis of rotation of a body Force induces linear acceleration Torque induces angular (rotational) acceleration  Kinematics: Spatial characteristics Position or location in space of the displacement: Position of a body can be described qualitatively (arm in abduction) or quantitatively (arm positioned with the elbow flexed 45 degree ) Position of person of body segment is important in injuries: Force applied to an arm in extension and external rotation will cause a different injury pattern if the same force is applied to an arm in flexed and internal rotation Head position: flexion or extension The rotatory or translatory displacement of a segment is commonly located in space by using the three-dimensional Cartesian coordinate system, borrowed from mathematics, as a useful frame of reference. Position of specific point or landmark on the body can be specified quantitatively using Cartesian coordinate system (x,y,z)or polar (r,Ѳ) The origin of the x-axis, y-axis, and z-axis of the coordinate system is traditionally located at the center of mass (CoM) of the human body, assuming that the body is in anatomic position (standing facing forward, with palms forward) At COM for body segment  Coordinate system  X-axis runs side to side in the body and is labeled in the body as the coronal axis;  Y-axis runs up and down in the body and is labeled in the body as the vertical axis  Z-axis runs front to back in the body and is labeled in the body as the anteroposterior (A-P) axis. Motion of a segment can occur either around an axis (rotation) or along an axis (translation). An unconstrained segment can either rotate or translate around each of the three axes, which results in six potential options for motion of that segment. The options for movement of a segment are alsoreferred to as degrees of freedom. Degree of Freedom (DOF): Degrees of freedom (DOF) correspond to the number of kinematic measurements needed to completely describe the position of an object. A 2D motion of a body segment point 2 degrees of freedom (DOF) Describes motion occurs around two axes (x and y) or (X and Z) or (Y and Z) coordinate and within two planes  The 3D motion of a body segment 6 degrees of freedom (DOF) 3 DOF of translation/ linear coordinates (x, y, z) 3 DOF of rotation/ angles to define the orientation of the segment) that must be specified. Arthrokinematics: (three small gliding or linear motions between the two joint surfaces) Osteokinematics (three anatomical rotations Flexion/extension, abduction/adduction, internal/ external rotation)  Degree of Freedom (DOF) A completely unconstrained segment has: 6 degrees of freedom (DOF) 3 DOF of translation 3 DOF of rotation Segments of human body are constrained one degree of freedom or all six degrees of freedom A relative frame of reference is measuring from a point that is free to move, like the motion of a foot relative to the hip or the plant foot relative to the soccer ball Kinematics: Spatial characteristics Direction of displacement of the segment Movement can be described as occurring Clockwise Counterclockwise Location & Direction of Displacement (Motion) Anatomic terms describing human movement are independent of viewer perspective and, therefore, more useful clinically “Physiological movement” Flexion and extension are motions of a segment occurring around the same axis and in the same plane (uniaxial or uniplanar) but in opposite directions. Flexion and extension generally occur in the sagittal plane around a coronal axis, although exceptions exist (carpometacarpal flexion and extension of the thumb). Flexion is the direction of segmental rotation that brings ventral surfaces of adjacent segments closer together Extension is the direction of segmental rotation that brings dorsal surfaces closer together. Relative Reference Systems All Joints @ 0except Ankle @ 90 Forearm varies Fundamental Anatomical Standing Standing Position Position  Standard Reference Terminology Anatomical Reference Planes  Cardinal planes – 3 imaginary perpendicular reference planes that divide the body in half by mass  Plane:  Sagittal plane: forward and backward movements of the body and body segments occur  Frontal plane: lateral movements of the body and body segments occur  Transverse plane: horizontal body and body segments movements occur when the body is in an erect standing position Standard Reference Terminology Anatomical Reference Axes An imaginary axis of rotation that passes through a joint to which it is attached Mediolateral axis: imaginary line around which sagittal plane rotations occur Anterioposterior axis: imaginary line around which frontal plane rotations occur Longitudinal axis: imaginary line around which transverse plane rotations occur These three axes are always associated with the same single plane – the one to which the axis is perpendicular Anatomical Planes and left portions and left halves  and back portions Transverse plane The horizontal plane dividing the body into upper and lower portions Also called the Horizontal plane Medial Rotation and lateral Rotation  Diagonal Planes of Motion A combination of more than one plane including parallel and perpendicular. In reality, most of our movements while exercising are diagonal. 1. High Diagonal Upper limbs at shoulder joints Overhand skills EX. Baseball Diagonal Planes of Motion 2. Low-upper Diagonal Upper limbs at shoulder joints Underhand skills EX. Discus Thrower 3. Low Diagonal Lower limbs at the hip joints EX. Kickers & Punters Axes of rotation For movement to occur in a plane, it must turn or rotate about an axis. The axes are named in relation to their orientation 14 I.Frontal (lateral or coronal) axis Has same orientation as frontal plane of motion & runs from side to side at a right angle to sagittal plane of motion Runs medial  lateral Commonly includes flexion, extension movements 15  Axes of rotation II. Sagittal (anteroposterior) axis Has same orientation as sagittal plane of motion & runs from front to back at a right angle to frontal plane of motion Runs anterior  posterior Commonly includes abduction, adduction II movements 16  Axes of rotation III. Long (vertical) axis Runs straight down through top of head & is at a right angle to transverse plane of motion Runs superior  inferior Commonly includes internal rotation, external rotation movements III 17  Joint Movements Osteokinematics/Physiological movements: Movements that the patient can do voluntarily, for example, the classic or traditional movements such as flexion, abduction and rotation. Arthrokinematics/accessory movements: Movements within the joint and surrounding tissues that are necessary for normal ROM but that cannot be performed by the patient. Terms that relate to accessory movements are: Component motions Joint play  Accessory/Component movements Component motions: Motions that company active motion but are not under voluntary control; the term is often used synonymously with accessory movements. Upward rotation of the scapula and clavicle, which occur with shoulder flexion, are component motions  Joint Play Joint Play Motions that occur between the articular surfaces which allow physiological movements of the joint to take place The movements are necessary for normal joint functioning through the ROM and can be demonstrated passively, but they cannot be performed actively by the patient. The movements include: Rolling Sliding Spinning Distraction Compression  Rolling: A rolling of one bone surfaces on another Slide: A sliding of one bone surface across another  Spin motion Rotation of segment about a stationary mechanical axis: 1. Spinning rarely occurs alone in joints of the body. - Humerus flexion/extension, femur with flexion/extension, and head of the radius with pronation/supination and Atlanto –Axial joint. Other accessory motions Accessory motions that affect the joint include: A. Compression B. Traction  Displacement: a body moves from one place to another (linear distance: from starting position to the ending position) regardless to the path Distance: measures how far the body has moved Angular displacement: measures number of degrees (or Radian) of rotation (knee flexed through angular rotation for 40 degrees)  Velocity: a vector measures of time rate of displacement Magnitude and direction Linear velocity Angular velocity Ex: 5m/s East Speed: is a scalar measure Magnitude with no direction Ex: 5 m/s  Acceleration: measure the time rate of change in body’s velocity Linear acceleration: expressed in unite of g; 1 g is the acceleration created byearth gravitational pull (9.81 m/s2 ) Angular acceleration Kinematics There are five kinematic variables that fully describe motion or displacement of a segment: 1. the type of displacement (motion) 2. the location and direction of displacement of the segment (motion) 3. the magnitude of the displacement 4. the rate of displacement or rate of change of displacement (velocity or acceleration) Goniometry used to measure the Magnitude of joint motion  Motion analysis Lab and VIDEOGRAPHY Are used to measures the magnitude, direction of kinematics: Displacement, velocity, acceleration,…  ROM measurement tools http://teamawesome34.wee bly.com Videotape Red line represent the position of the left wrist during in golf Blue line represents the body Center of Mass  Rearfoot Angle Rearfoot Moment EV 15 0.1 0.05 Moment (N*m/ Kg*ht) 10 RFS Ang (deg). 0 5 -0.05 0 -0.1 -0.15 -5 -0.2 -10 -0.25 INV 0 20 40 60 80 100 20 40 60 80 100 INV % Stance % Stance No Change in Angle Reduced Load on Invertors NO Laughton et al, 2001 Orthotic  Knee Transverse Knee Frontal IR ADD 5 Angle (deg) -1 Angle (deg) 0 -5 -3 -10 -5 -15 -7 ER 0 20 40 60 80 100 ABD 20 40 60 80 100 % stance % stance Knee IR decreased Knee ABD decreased NO Laughton et al, 2001 Orthotic  Kinematic Motion is change in position with respect to some frame of reference Displacement: a body moves from one place to another (linear distance: from starting to the ending position regardless to the path Final change in position Vector quantity Distance: measures how far the body has moved Sum of all changes in position Scalar quantity – Because distance is a scalar, your odometer does not tell you in what direction you are driving Angular displacement: measures number of degrees (or Radian) of rotation (knee flexed through angular rotation for 40 degrees)  Kinematic Rate of Displacement: The displacement per unit time Velocity: a vector measures displacement per unit time in a given direction – Magnitude and direction – Linear velocity: velocity of a translating segment is expressed as meters per second (m/sec) – Angular velocity (velocity of a rotating segment) is expressed as degrees per second (deg/sec) – Angular velocity – Ex: 5m/s East Speed: a scalar measure of displacement per unit time regardless of direction – Magnitude with no direction – Ex: 5 m/s with no direction Acceleration: a measure of change in velocity per unit time is acceleration – The units for acceleration are meters per second squared (m/sec2) – Linear acceleration: expressed in unite of g; 1 g is the acceleration created by earth gravitational pull (9.81 m/s2 ) – angular acceleration is given as degrees per second squared (deg/sec2) An electrogoniometer or a three-dimensional motion analysis system allows documentation of the changes in displacement over time.  Linear Kinematics - Variables Position where an object is in space relative to a global coordinate system Displacement change in an object’s position independent of direction Velocity (vector) rate of change in position; V = (p2-p1)/(t2-t1) – Horizontal Velocity; Vh = (x2-x1)/(t2-t1) Vh – Vertical Velocity; Vv = (y2-y1)/(t2-t1)2 – Resultant Velocity; Vr = √Vh + V2 V v Vv r Acceleration (vector) Rate of change in velocity; a = (v2-v1)/(t2-t1) Horizontal, Vertical, Resultant  Angular Kinematics Angular Position () Joint Angle relative angle between two adjacent segments (e.g. upper arm & forearm compose elbow angle)  Elbow Angular Velocity () rate of change in angular position  = (2-1)/(t2-t1)  Shank Angular Acceleration () rate of change in angular velocity  = (2-1)/(t2-t1) Distance= Displacement= Speed= Velocity=  Movement displacement and velocity This graph shows the angular displacement and angular velocity of a simple elbow extension and flexion movement in the sagittal plane Ext:Fast Fle:slow The displacement graph shows the elbow extension first then the flexion. Extension was faster than flexion may be because addition of the book’s weight. The velocity graph shows that the forearm start to speed up till reached the highest velocity which lasted for very short period and then started to slow down till it reached Zero. Zero velocity in the middle of the graph associated with the end of extension motion. The velocity of the flexion was slower and in the negative direction.  Isokinetic Isokinetic (iso = constant or uniform, kinetic = motion) – Dynamometers device – Same angular velocities – Prevent angular acceleration beyond the set speed  Mechanics of motion Statics Dynamics constant state of acceleration motion present Kinetics of Constant Kinematics Kinetics motionless systems velocity systems Kinematics Kinetics  KINETICS Examines the causes of motion, the internal and external forces that cause motion or cause a body to remain at rest, and the interactions between these forces. There are two branches of kinetics; STATICS and DYNAMICS Linear kinetic– if the force is enough to overcome the body’s resistance to movement, the body moves linear – Examines the relation between a body’s resistance to change in its linear state of motion and effect of applied forces – Mass, inertia, Force Angular Kinetic – causes of angular motion\ – Examines relation between a body’s resistance to change in angular state of motion and effect of applied torque Includes moment of force and moment of inersia  Linear Kinetic Mass: quantity of matter in a body (kg) The greater the mass the more difficult it is to move Inertia: is the body’s resistance to being moved linearly – The property of matter by which it remains at rest or in uniform motion in a straight line (i.e. constant velocity) – To move an object that is at rest we have to overcome its inertia or the tendency to remain stationary – In angular movement: Moment of inertia: resistance to a change in a body’s state of angular motion  FORCE Force = “is a push or pull that changes a body's state of rest or motion” Force is the mechanical action or effect applied to a body that tends to produce acceleration Force is a vector quantity with magnitude , direction, orientation, and point of application Gravity does not have direct physical contact with objects – Has an effect at the center of mass of a segment A force (F) induces acceleration (a) of the object to which the force is applied – Force = (mass(kg))(acceleration(m/sec2)) or F = (m)(a) – Acceleration being directly proportional to the mass (m) of that object The unit for force is actually kg-m/sec2 (Newton) – A newton is the force required to accelerate 1 kg at 1 m/sec2  Force Gravity (g): the attraction of the Earth’s mass to another mass Weight (W) of an object is the pull of gravity on the object’s mass with an acceleration of 9.8 m/sec2 in the absence of any resistance: – Weight = (mass)(gravity) or W= (m)(g) Gravity acts on each unit of mass that composes an object – There is an infinite number of force vectors, however we create a single force vector (idealized force vector) that represents the net effect – Gravity acting on an object at the point of application “Center of mass (CoM)” or center of gravity (CoG) of that object or segment It is common to see weight given in kilograms (kg) instead of Newton (N)  FORCE Internal Forces – generated from the body’s own structure: Forces due to muscle contraction ligaments(pull of a ligament on bone) Bones (the push of one bone on another bone at a joint) Blood/ fluid flow Internal forces essential for – Initiation of movement – Control or counteract movement produced by external forces In muscle the point of application is the insertion “ fixed point” Point of application is located with respect to joint center of rotation  Force External Forces: pushes or pulls on the body that arise from sources outside the body – Gravity – Wind (push of air on the body) – Water (push of water on the body) – Other objects (the push of floor on the feet, the pull of a weight boot on the leg) Facilitate or restrict movement  FORCES In sport athletes primarily produce force within the body by contracting the muscles. Types of Forces Muscular Gravitational Frictional Contact (ground or another body), Inertial Elastic  TYPES OF FORCES Muscular Force = due to the contraction of muscle. Friction Force = due to two surfaces in contact with each other and the tendency of the two surfaces to oppose each others motion e.g.. mountain bike vs. racing bike tires, sports shoe soles for various sports Gravity = is the downward acting force which attracts bodies to the centre of the earth.  Contact = the force involved in a collision of bodies or the ground. e.g.. Scrum or Tackling collisions in rugby, hitting or catching a baseball, running Inertia = the force of an object due to its mass (whether moving or stationary) e.g.. catching a basketball vs. tennis ball moving a car of a book  Injury-causing situations Several factors combine to determine the nature of injury, severity of injury, and tissues injured: Magnitude: how much force is applied? Location: where on the body Direction of force Duration of application (time) Frequency: how often is the force applied? Variability: is the magnitude constant or variable over the application interval? Rate: how quick is the force applied?  Force It is common to have multiple forces at the same time, categorize multiple forces as force system: Type of force systems: – Linear forces: Forces with the same orientation and line of action Can be varied by the magnitudes and directions F1 F2 – Parallel forces: Forces with the same orientation but different line of action Force vectors parallel to each other Forces along axis and moments – Concurrent force system – General force system: Force system does not fall under other system – Force Coupled system – Parallel and oppositely direct forces Force coupled system  Force Free body diagram: A simple graphic representation of all forces acting in the system For biomechanical analysis – Gravity is represented as one vector  Center of Mass (CoM) Mass of the body or body segment distribution is reduced to a single point that represent the entire body or the entire segment – Used for simplification – For each body or segment there is center of mass or center of gravity at which is we concentrate the body’s or segment’s mass into a point mass – This point mass would move exactly the same as the body would in its distributed state – Center of mass and center of gravity (CoG) are located in the same point – Mass must be evenly distributed around the CoM – Human body’s CoM typically is located within the body’s boundaries – Gravitational vector is commonly referred to as the line of gravity (LoG) – CoG: acts as balanced point Symmetrical object: CoM is located in the geometric center Asymmetrical object: CoM is located toward the heavier end  Segmental Centers of Mass and Composition of Gravitational Forces 2 or more segments can be treated as a single segment with CoM The CoM for any one object or rigid series of segments will remain unchanged regardless of the position When an object is composed of two or more linked and movable segments CoM of the combined unit will change if the segments are rearranged in relation to each other – point of application of gravity will change with regard to the joint or center of rotation  Center of Mass CoM of the body lies approximately anterior to the second sacral vertebra (S2) Reaction board: Under one end of the board is a scale Center of Mass of the Human Body – With rearrangement of body segments the location of the individual’s CoM will potentiallychange – The amount of change in the location of the CoM depends on how disproportionately the segments are rearranged – The location of the CoM of an object or the body depends on the distribution of mass of theobject  Posture Analysis Good posture is about more than standing up straight so you can look your best.  It is an important part of your long-term health.  Making sure that you hold your body the right way, whether you are moving or still, can prevent pain, injuries, and other health problems.  In an ideal posture, the line of gravity should pass through specific points of the body. This can simply be observed or evaluated using a plumb line to assess the midline of the body.  This line should pass through the lobe of the ear, the shoulder joint, the hip joint, though the greater trochanter of the femur, then slightly anterior to the midline of the knee joint and lastly anterior to the lateral malleolus.  When viewed from either the front or the back, the vertical line passing through the body’s centre of gravity should theoretically bisect the body into two equal halves, with the bodyweight distributed evenly between the two feet.  While assessing posture, symmetry and rotations/tilts should be observed in the anterior, lateral and posterior views.\  Assess: Head alignment Cervical, thoracic and lumbar curvature  Shoulder level symmetry Pelvic symmetry Hip, knee and ankle joints posture analysis system analyses the standing posture of the patient. Its posture analysis protocol identifies key postural deviations from multiple views & exports all data to a report.