KINESIOLOGY – BIOMECHANICS HANDBOOK PDF 2021-22
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Uploaded by AttentiveSalmon
University of Zimbabwe
2021
Dr JM Dambi
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Summary
This handbook provides a comprehensive overview of kinesiology and biomechanics for BSc (Hons) Physiotherapy & Occupational Therapy students at the University of Zimbabwe (2021-2022). It covers modules on introduction, muscle mechanics, neuromuscular control, biological tissue, and arthrology. The handbook outlines course content, assessment criteria, and recommended texts.
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KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (Hons) Physiotherapy & Bsc (Hons) Occupational Therapy II (2019-20)...
KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (Hons) Physiotherapy & Bsc (Hons) Occupational Therapy II (2019-20) Department of Rehabilitation College of Health Sciences University of Zimbabwe Compiled by DR JM DAMBI PhD PHYSIOTHERAPY (UNIVERSITY OF CAPE TOWN) i KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 TABLE OF CONTENTS OBJECTIVE.......................................................................................................................................................... 1 COURSE CONTENT.............................................................................................................................................. 1 MODULE 1: INTRODUCTION........................................................................................................................... 1 MODULE 2: MUSCLE MECHANICS................................................................................................................... 1 MODULE 3: NEUROMUSCULAR CONTROL OF MOVEMENT - INTRODUCTION................................................. 1 MODULE 4: MECHANICAL PROPERTIES OF BIOLOGICAL TISSUE...................................................................... 1 MODULE 5: ARTHROLOGY.............................................................................................................................. 2 COURSE ASSESSMENT........................................................................................................................................ 2 RECOMMENDED TEXTS...................................................................................................................................... 2 PROGRAM.......................................................................................................................................................... 3 1 MODULE 1: INTRODUCTION....................................................................................................................... 4 1.1 Module Outline................................................................................................................................. 4 1.2 Basic concepts & definitions.............................................................................................................. 4 1.3 Application of Newton's Laws of motion to the human body............................................................. 4 1.3.1 First law of motion.................................................................................................................... 4 1.3.2 Second law of motion............................................................................................................... 5 1.3.3 Newton’s third law of motion................................................................................................... 5 1.4 Analysis of law of moments and its application to the body............................................................... 6 1.4.1 Law of moments....................................................................................................................... 6 1.4.2 Stability..................................................................................................................................... 7 1.5 Simple machines.............................................................................................................................. 10 1.5.1 Levers..................................................................................................................................... 10 1.5.2 Pulleys..................................................................................................................................... 12 1.6 Resolution of forces......................................................................................................................... 12 1.6.1 Effects of forces...................................................................................................................... 12 1.6.2 Composition of forces............................................................................................................. 13 2 MODULE 2: MUSCLE MECHANICS............................................................................................................ 14 2.1 Module outline................................................................................................................................ 14 2.2 Introduction.................................................................................................................................... 14 2.2.1 Nomenclature......................................................................................................................... 14 2.2.2 Muscle histology..................................................................................................................... 14 2.2.3 Sliding filament theory............................................................................................................ 15 2.3 Muscle fibre classification................................................................................................................ 15 2.3.1 Parallel muscles...................................................................................................................... 15 2.3.2 Oblique-fibered muscles......................................................................................................... 17 ii KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.4 Functional characteristics of muscle tissue...................................................................................... 19 2.4.1 Irritability................................................................................................................................ 19 2.4.2 Contractility............................................................................................................................ 19 2.4.3 Extensibility............................................................................................................................. 19 2.4.4 Elasticity.................................................................................................................................. 19 2.5 Length-tension relationships........................................................................................................... 19 2.5.1 Active insufficiency................................................................................................................. 21 2.5.2 Passive insufficiency................................................................................................................ 22 2.5.3 Force velocity relationship...................................................................................................... 23 2.6 Types of muscle contraction............................................................................................................ 24 2.6.1 Concentric contraction............................................................................................................ 24 2.6.2 Eccentric contraction.............................................................................................................. 24 2.6.3 Isometric contraction.............................................................................................................. 24 2.6.4 Functional roles of muscles..................................................................................................... 25 2.7 Factors affecting force production................................................................................................... 25 2.7.1 Type of muscle fibers.............................................................................................................. 26 2.7.2 Number of mm fibers.............................................................................................................. 26 2.7.3 Rate of Stimulation................................................................................................................. 27 2.7.4 Percentage of Fiber Recruitment............................................................................................. 28 2.7.5 Force-Velocity Relationship..................................................................................................... 28 2.7.6 Fiber Architecture................................................................................................................... 28 2.7.7 Muscle Temperature............................................................................................................... 28 2.7.8 Proportional Length of Muscle................................................................................................ 29 2.7.9 Angle of Pull............................................................................................................................ 29 3 MODULE 3: NEUROMUSCULAR CONTROL OF MOVEMENT – INTRODUCTION.......................................... 30 3.1 Module outline................................................................................................................................ 30 3.2 Introduction.................................................................................................................................... 30 3.3 Overview of relevant neuroanatomy and neurophysiology.............................................................. 32 3.3.1 Cerebellum............................................................................................................................. 32 3.3.2 Basal Ganglia........................................................................................................................... 32 3.3.3 Reticular formation................................................................................................................. 33 3.3.4 Cerebral Cortex....................................................................................................................... 34 3.3.5 Reflex arc................................................................................................................................ 35 3.3.6 The Alpha Motor Neuron........................................................................................................ 37 3.4 Muscle spindle................................................................................................................................. 37 3.4.1 Mechanism of action............................................................................................................... 39 iii KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 3.5 Golgi Tendon Organ (GTO)............................................................................................................... 39 3.5.1 Summary of mechanism of action of GTO............................................................................... 40 3.6 Control of movement...................................................................................................................... 40 3.6.1 Reflex movement Control....................................................................................................... 41 3.6.2 Voluntary movement.............................................................................................................. 42 4 MODULE 4: MECHANICAL PROPERTIES OF BIOLOGICAL TISSUE................................................................ 43 4.1 Module outline................................................................................................................................ 43 4.2 Introduction.................................................................................................................................... 43 4.3 Important terminology.................................................................................................................... 43 4.4 Strength of Biological Materials....................................................................................................... 43 4.5 Load-deformation relationship........................................................................................................ 44 4.5.1 Type of loading....................................................................................................................... 44 4.6 Structural vs. Material Properties.................................................................................................... 45 4.7 Stress –strain relationship............................................................................................................... 46 4.7.1 Stress...................................................................................................................................... 46 4.7.2 Strain...................................................................................................................................... 46 4.7.3 Young’s modulus..................................................................................................................... 47 4.7.4 Relationship between strain & stress...................................................................................... 47 4.7.5 Typical load-deformation curve............................................................................................... 47 4.8 Typical Stress-Strain Curve............................................................................................................... 48 4.8.1 Concept 1: Elastic & plastic regions......................................................................................... 48 4.8.2 Concept 2: Stiffness (elastic modulus)..................................................................................... 49 4.8.3 Concept 3: Yield point............................................................................................................. 50 4.9 Tissue mechanical properties.......................................................................................................... 50 4.10 Viscoelasticity.................................................................................................................................. 53 4.10.1 Creep...................................................................................................................................... 53 4.10.2 Force- relaxation..................................................................................................................... 54 4.11 Applied biomechanics of biological tissues...................................................................................... 54 4.12 Mechanical properties of bone tissue.............................................................................................. 55 4.12.1 Introduction............................................................................................................................ 55 4.12.2 Ductile vs. Brittle..................................................................................................................... 56 4.12.3 Viscoelastic Properties: Rate Dependency of Cortical Bone..................................................... 56 4.12.4 Effects Chronic Physical Activity.............................................................................................. 57 4.12.5 Effects of Age on bone tissue.................................................................................................. 57 4.13 Mechanical properties of ligaments & muscle-tendon units............................................................ 58 4.13.1 Strain-stress curve of collagenous tissue................................................................................. 58 iv KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 4.14 Mechanical properties of ligamentous tissue................................................................................... 59 4.14.1 Clinical –sprain........................................................................................................................ 60 4.14.2 Effects of disuse in the mechanical properties of ligamentous tissue...................................... 60 4.14.3 Effects of corticosteroids on ligaments.................................................................................... 60 4.15 Mechanical properties of tendon tissue........................................................................................... 61 4.15.1 Elasticity of tendon................................................................................................................. 61 4.16 Mechanical properties of muscle tissue........................................................................................... 61 4.16.1 Effects of tissue on mechanical properties.............................................................................. 62 5 MODULE 5: ARTHROLOGY........................................................................................................................ 63 5.1 Module outline................................................................................................................................ 63 5.2 Basic terminology............................................................................................................................ 63 5.3 Functions of joints........................................................................................................................... 63 5.4 Classification of joints...................................................................................................................... 63 5.5 Structural classification of joints...................................................................................................... 64 5.5.1 Fibrous joints.......................................................................................................................... 64 5.5.2 Cartilaginous joints.................................................................................................................. 65 5.5.3 Synovial joints......................................................................................................................... 67 5.6 Classification based on function...................................................................................................... 68 5.6.1 Synarthrosis............................................................................................................................ 69 5.6.2 Amphiarthrosis (cartilaginous joints)....................................................................................... 69 5.6.3 Diarthrosis (Synovial Joints)..................................................................................................... 69 5.6.4 Summary of joint classification................................................................................................ 70 5.7 Types of joints................................................................................................................................. 70 5.7.1 Ball and Socket Joint............................................................................................................... 71 5.7.2 Hinge joint.............................................................................................................................. 71 5.7.3 Saddle joint............................................................................................................................. 71 5.7.4 Pivot joint................................................................................................................................ 72 5.7.5 Condyloid joint........................................................................................................................ 72 5.7.6 Sliding or gliding joint.............................................................................................................. 73 5.7.7 Summary- types of joints......................................................................................................... 73 5.8 Description of mvt........................................................................................................................... 73 5.9 Osteokinematics.............................................................................................................................. 73 5.10 Arthrokinematics............................................................................................................................. 74 5.10.1 Roll.......................................................................................................................................... 75 5.10.2 Spin......................................................................................................................................... 75 5.10.3 Glide....................................................................................................................................... 75 v KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 5.10.4 Compression & distraction...................................................................................................... 76 5.11 Convex-concave & concave-convex rule.......................................................................................... 76 5.12 Joint positions................................................................................................................................. 77 5.12.1 Close-packed positions............................................................................................................ 77 5.12.2 Summary – loose- & close packed positions............................................................................ 78 vi KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 OBJECTIVE At the conclusion of the course the student will be able to discuss and apply the principles of biomechanics, muscle function, joint anatomy and physiology which interact to produce or limit normal as well as pathological motion. COURSE CONTENT MODULE 1: INTRODUCTION 1. Application of Newton's Laws of motion to the human body 2. Analysis of law of moments and its application to the body 3. Levers as applied to the human body 4. Free force diagrams and resolution of muscle forces 5. Analysis of mechanical factors that influence the turning force generated at joints MODULE 2: MUSCLE MECHANICS 1. Mechanical properties of muscle 2. Isometric and isotonic contractions 3. Length/tension curves 4. Relationship between structure and function - fibre type and morphology 5. Synergistic muscle action 6. Spurt/shunt muscle action 7. Factors that influence force production MODULE 3: NEUROMUSCULAR CONTROL OF MOVEMENT - INTRODUCTION 1. Levels of integration of the control of movement in the nervous system 2. The muscle spindle 3. Facilitatory and inhibitory influences on the final common pathway MODULE 4: MECHANICAL PROPERTIES OF BIOLOGICAL TISSUE 1. Stress/ strain 2. Elastic modulus, stiffness of matter 3. Lubrication 4. Viscoelasticity 1 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 MODULE 5: ARTHROLOGY 1. Structure and function of joints 2. Osteokinematics 3. Close-packed and loose packed position COURSE ASSESSMENT 1. Pre and post-lecture quizzes – 40% 2. End of semester exam – 60% 3. Professional exam – Biomechanics section constitute 45% of the final mark RECOMMENDED TEXTS 1. Clinical Kinesiology and Anatomy-Lynn S. Lippert (Fifth Edition) 2. Functional anatomy: musculoskeletal anatomy, kinesiology, and palpation for manual therapists - Christy Cael 3. Applied Kinesiology: A Training Manual and Reference Book of Basic Principles and Practice- Robert Frost 2 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 PROGRAM LECTURE TOPIC Date – Time 1 Introduction to Kinesiology – objectives, learning materials & course assessment 2 Newton’s laws of motion, law of moments & stability 3 Simple machines 3 Resolution of forces & module 1 recap 4 Introduction to muscle mechanics, mm fibre classification, functional characteristics of muscles 5 Length tension relationships & types of muscle contraction 6 Functional roles of muscles, factors affecting force production & module 2 recap 7 Introduction to module 3, overview of relevant neuroanatomy and neurophysiology 8 Muscle spindle, GTO, Control of movement & recap of module 3 9 Introduction to module 4, load-deformation relationship 10 Structural vs. Material Properties, Stress –strain relationship, viscoelasticity 11 Applied biomechanics to biological tissue, Mechanical properties of bone tissue 12 Mechanical properties of ligaments & muscle-tendon units, module 4 recap 13 Introduction to module 5, classification of joints 14 Description of mvt., Convex-concave & concave-convex rule, Joint positions, recap of module 5 15 Revision: modules 1 & 2 16 Revision: module 3, 4 & 5 17 End of semester examination 18 Feedback on end of semester examination 3 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 1 MODULE 1: INTRODUCTION 1.1 Module Outline 1. Basic concepts & definitions 2. Application of Newton's Laws of motion to the human body 3. Analysis of law of moments and its application to the body 4. Levers as applied to the human body 5. Free force diagrams and resolution of muscle forces 6. Analysis of mechanical factors that influence the turning force generated at joints 1.2 Basic concepts & definitions Force- is a push or pull action. Force is a vector quantity Friction - is a force developed by two surfaces, which tends to prevent motion of one surface across another Inertia- is the property of matter that causes it to resist any change of its motion in either speed or direction Kinematics - Kinetics - is a description of motion with regard to what causes motion Mass - the amount of matter that a body contains normal resting length of a mm -length of a muscle when it is unstimulated, that is, when there are no forces or stresses placed upon it Torque/ moment/moment of force - is the ability of force to produce rotation about an axis Vector - is a quantity having both magnitude and direction (e.g.) pressure, velocity etc. 1.3 Application of Newton's Laws of motion to the human body 1.3.1 First law of motion an object at rest tends to stay at rest, and an object in motion tends to stay in motion Often referred to as the law of inertia (N.B –what is inertia??) A force is needed to overcome the inertia of an object and cause the object to move, stop, or change direction Clinical application- Whiplash injuries Typical exam question – describe the biomechanics of a Whiplash injuries? (10 marks) 4 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 1.3.2 Second law of motion Also known as the law of acceleration (N.B – acceleration??) The amount of acceleration depends on the strength of the force applied to an object F=ma Reading assignment: what are the clinical applications of the second law of motion? 1.3.3 Newton’s third law of motion the law of action-reaction For every action there is an equal and opposite reaction The strength of the reaction is always equal to the strength of the action, and it occurs in the opposite direction E.g. Gravitational F & ground reactional F 5 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 1.4 Analysis of law of moments and its application to the body 1.4.1 Law of moments Torque/moment of force - is the ability of a force to produce rotation about an axis Clinical definition -torque is the amount of force needed by a muscle contraction to cause rotary joint motion The amount of torque a lever has depends on the amount of force exerted and the distance it is from the axis Torque=F*s i.e. torque about any point (axis) equals the product of the force magnitude & its perpendicular distance from the line of action of the force to the axis of rotation NB- The perpendicular distance is called the moment arm or torque arm Law of moments – in a state of equilibrium, the sum of clockwise moments is equal to the sum of anti-clockwise moments Torque is greatest when the angle of pull is at 90 degrees (why is that so???) Torque decreases as the angle of pull either decreases or increases from that perpendicular position Clinical - a muscle is most efficient at moving a joint or rotating when the joint is at 90 degrees. It becomes less efficient at moving or rotating when the joint angle is either increasing or decreasing No torque is produced if the force is directed exactly through the axis of rotation – remember Torque=F*s? E.g. if the biceps contracts when the elbow is nearly or completely extended, there is very little torque produced as the perpendicular distance is zero or close to zero. T=xsinα and sin 180=0, where αis the angle of pull of the muscle. Torque=F*s and as such: the amount of torque determines the effect a force (muscle pull/action) has on the joint When the perpendicular distance between the joint axis and the line of pull is very small, the force generated by the muscle is primarily a stabilizing force 6 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 When the perpendicular distance between the joint axis and the line of pull is very large (peak@ 90*??)), the force generated by the muscle is primarily an angular force. Most of the force generated by the muscle is directed at rotating the joint and not stabilizing the joint As a muscle contracts through its ROM, the amount of angular or stabilizing force changes As the muscle increases its angular force, it decreases its stabilizing force and vice versa At 90 degrees, or halfway through its range, the muscle has its greatest angular force Past 90 degrees, the stabilizing force becomes a dislocating force because the force is directed away from the joint 1.4.2 Stability 1.4.2.1 Equilibrium Based on the Law of moments/equilibrium Law of equilibrium- when in equilibrium, the sum of the forces and torques equal zero Called “static equilibrium” when an object is at rest (Newton’s 1st law) & has to fulfil the following 2 conditions: First Condition: Ʃ F = 0 (sum of forces equal zero) Second Condition: ƳM = 0 (sum of torques equal zero) 1.4.2.2 Relationship between BOS & COG state of equilibrium is depends primarily on the relationship between the object’s centre of gravity (COG) & base of support (BOS) COG is the balance point of an object at which torque on all sides is equal (location in humans??)) BOS is that part of a body that is in contact with the supporting surface 7 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 1.4.2.3 Factors that affect stability and balance in physical activity in humans 1) Position of pt.'s COG 2) Size of the BOS 3) Number of points in contact with the floor e.g. 2/3 point gait pattern 4) Mass of the object Clinical: 2pt/3/4-pt gait Bed mobility exercises Reading assignment/typical exam question: Mr X was involved in a road traffic accident (RTA) and sustained a mid-femur fracture. The fracture was managed by the insertion of a K-nail. The therapist initially mobilized Mr X a walking frame before progressing to two elbow crutches. Mr X is now mobilizing with one elbow crutch. With reference to biomechanical principles, explain the mobilization sequence of Mr X. 10 marks 1.4.2.4 States of equilibrium Equilibrium can be static or dynamic There are basically three states of static equilibrium i.e. 1. Stable 2. Unstable 3. Neutral All in relation to gravitational potential energy & position of the COG 8 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 1.4.2.4.1 Stable equilibrium occurs when an object is in a position that to disturb it would require its COG to be raised Potential energy is at a minimal Removal of force will result in the object returning to its neutral position For humans – lying flat on a horizontal surface Clinical application - Stroke rehabilitation - start with activities in sup/prone i.e. bed activities e.g. rolling 1.4.2.4.2 Unstable equilibrium occurs when only a slight force is needed to disturb an object e.g. a person standing on one leg Potential energy is at its maximal Little force is needed to move LOG outside BOS 1.4.2.4.3 Neutral equilibrium exists when an object’s COG is neither raised nor lowered when it is disturbed minimum potential energy & small BOS 1.4.2.5 Dynamic Equilibrium Varies between neutral & unstable equilibrium with activities such as walking Normal postural reflex mechanism necessary for attainment of balance 1.4.2.6 The relationships between balance, stability, and motion The lower the COG, the more stable the object The COG and LOG must remain within the BOS for an object to remain stable 9 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 The wider the BOS, the more stable the object e.g. a toddler learning to walk & use of mobility aids in ambulation Stability increases as the BOS is widened in the direction of the force The greater the mass of an object, the greater its stability The greater the friction between the supporting surface and the BOS, the more stable the body will be 1.5 Simple machines A machine is a device which makes easier They are 3 types of simple machines namely: 1. Levers 2. Inclined planes 3. Pulleys 1.5.1 Levers They are 3 types of levers Differentiated from the differences in arrangement of the Load (L), Effort (E) & Pivot/Fulcrum (P/F) 1.5.1.1 First-Class Levers (EFR) Point of axis/fulcrum is (F) between two forces, Effort (E) and Resistance (R) 10 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 One force will tend to rotate the object clockwise, the other will tend to rotate the object counterclockwise The distance from the axis can determine the magnitude of force needed to keep equilibrium Axis force will equal the sum of effort and resistance 1.5.1.2 Second-Class Levers (FRE) Resistance is between the axis and effort Magnitude of effort is always less than resistance?? Example: wheelbarrow 11 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 1.5.1.3 Third-Class Levers (FER) Effort between resistance and axis Magnitude of effort is always greater than resistance?? Resistance will always move faster and farther than effort Force at axis will be less than at effort 1.5.2 Pulleys A pulley consists of a grooved wheel that turns on an axle with a rope or cable riding in the groove The functions of a pulley are: 1) change the direction of a force e.g. peroneus longus 2) increase or decrease the magnitude of a force e.g. quads A fixed pulley is a simple pulley attached to a beamy It acts as a first-class lever with F on one side of the pulley (axis) & R on the other It is used only to change direction E.G. lateral malleolus of the fibula acts as a pulley for the tendon of the peroneus longus & changes its direction of pull 1.6 Resolution of forces Force is a push or a pull that alters the state of motion of a body 1.6.1 Effects of forces A force can cause… 12 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 1. A body at rest to move 2. A moving body to change direction 3. A moving body to accelerate 4. A moving body the decelerate 5. A body to change its shape Factors which affect the extent of these effects include: 1. Size of the force (how many Newtons) 2. Application of force 3. Direction of the force 1.6.2 Composition of forces Combining forces is called the composition of forces The process of dividing forces is called resolution of forces When 2 or more forces are subjected on an object, the single force is called a resultant of the forces Because forces are vectors, most all forces are associated with arrows to which the forces are pushing or pulling 13 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2 MODULE 2: MUSCLE MECHANICS 2.1 Module outline 1. Introduction 2. Mechanical properties of muscle 3. Isometric and isotonic contractions 4. Length/tension curves 5. Relationship between structure and function - fibre type and morphology 6. Synergistic muscle action 7. Spurt/shunt muscle action 8. Factors that influence force production 2.2 Introduction 2.2.1 Nomenclature * Muscle names tend to fall into one or more of the following categories: 1. Location e.g. tibialis ant 2. Shape e.g. trapezius 3. Action e.g. extensor carpi ulnaris 4. Number of heads or divisions e.g. triceps 5. Attachments = origin/insertion e.g. sternocleidomastoid 6. Direction of the fibres e.g. external and internal oblique 7. Size of the muscle e.g. pec major and pec minor 2.2.2 Muscle histology 14 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.2.3 Sliding filament theory relative movement of actin & myosin filaments yields active sarcomere shortening Myosin heads or cross-bridges generate contraction force 2.3 Muscle fibre classification 2.3.1 Parallel muscles fibres tend to be longer, thus having a greater range of motion potential 15 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.3.1.1 Strap muscles Are long and thin with fibres running the entire length of the muscle e.g. Sartorius, rectus abdominis 2.3.1.2 Fusiform has a shape similar to that of a spindle It is wider in the middle and tapers at both ends where it attaches to tendons Most, but not all, fibers run the length of the muscle The muscle may be any length or size, from long to short E.g. elbow flexors?? the biceps, brachialis, and brachioradialis muscles 2.3.1.3 Rhomboid * is four-sided, usually flat, with broad attachments at each end * E.g. the gluteus maximus, rhomboid minor & major 16 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.3.1.4 Triangular * are flat and fan shaped with fibers radiating from a narrow attachment at one end to a broad attachment at the other * E.g. pectoralis 2.3.2 Oblique-fibered muscles have a feather arrangement in which a muscle attaches at an oblique angle to its tendon The diff types of oblique-fibered muscles are : 1. unipennate 2. bipennate 3. Multipennate 17 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.3.2.1 Unipennate muscles * look like one side of a feather * There are a series of short fibers attaching diagonally along the length of a central tendon * E.g. tibialis posterior 2.3.2.2 Bipennate muscle * pattern looks like that of a common feather * Its fibers are obliquely attached to both sides of a central tendon * E.g. The rectus femoris muscle 18 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.3.2.3 Multipennate muscles * have many tendons with oblique fibers in between * E.g. deltoid 2.4 Functional characteristics of muscle tissue Muscle tissue possesses the following characteristics: 1. Irritability 2. contractility 3. Extensibility 4. Elasticity 2.4.1 Irritability * is the ability to respond to a stimulus i.e. a mm contracts when stimulated 2.4.2 Contractility * is the ability to shorten or contract when it receives adequate stimulation * This may result in the muscle shortening, staying the same, or lengthening (types of contractions???) 2.4.3 Extensibility * is the ability of a mm to stretch or lengthen when a force is applied 2.4.4 Elasticity * is the ability to recoil or return to normal resting length when the stretching or shortening force is removed 2.5 Length-tension relationships * Tension refers to the force built up within a muscle * The total tension of a mm is a combination of passive (non-contractile) & active (contractile units) tension 19 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 * Generally, mm are capable of being shortened to approx. 1/2 of its normal resting length & stretched about 2X * Excursion- is that distance from max elongation to max shortening * Usually a muscle has sufficient excursion to allow the joint to move through the joint’s entire range * The action responsible for the contraction of a muscle occurs within a sarcomere * force generation is dependent on the amount of overlap between thin and thick myofilament * The greater the number of cross bridges attached to the actin filaments, the larger the contraction force * 20 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 * One of the factors determining the amount of tension in a muscle is its length * There is an optimum range of a muscle within which it contracts most effectively * Force is dependent on the number of cross bridges formed * However, muscle also has connective tissue that behaves somewhat like a stiff elastic band 2.5.1 Active insufficiency * a 2 joint mm cannot exert enough tension to shorten to allow full ROM in both joints at the same time * E.g. Hamstrings 21 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.5.2 Passive insufficiency * a 2 joint mm cannot stretch enough to allow full ROM in both joints at the same time * occurs when a muscle cannot be elongated any farther without damage to its fibers * Passive insufficiency occurs to the antagonist 22 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.5.3 Force velocity relationship 23 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.6 Types of muscle contraction 2.6.1 Concentric contraction * Muscle contracts and shortening, positive work was done on external load by muscle * Tension in a muscle decreases as it shortens 2.6.2 Eccentric contraction * Muscle contracts and lengthening, external load does work on muscle or negative work done by muscle * Tension in a muscle increases as it lengthens by external load * Increased tensions in eccentric due to: 1. Cross bridge breaking force > holding force at isometric length 2. High tendon force to overcome internal damping friction 2.6.3 Isometric contraction 24 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.6.4 Functional roles of muscles * Muscles assume different roles during joint motion, depending on such variables as : 1. the motion being performed 2. the direction of the motion 3. the amount of resistance the muscle must overcome * If any of these variables change, the muscle’s role may also change * A muscle can assume the following roles: 1. Agonist/prime mover - is a muscle or muscle group that causes the motion e.g.?? 2. Assisting mover – muscle that is not as effective but does assist in providing that motion e.g.?? Factors that determine whether a muscle is a prime mover or an assisting mover include : i. Size ii. angle of pull iii. leverage iv. contractile potential 3. An antagonist is a mm that performs the opp motion of the agonist 4. The antagonist has the potential to oppose the agonist, but it is usually relaxed while the agonist is working. However, other task require simultaneous contraction of both antagonist & agonist, this is referred to as co-contraction. A co-contraction occurs when there is a need for accuracy 5. A stabilizer/fixator- is a muscle or muscle group that supports, or makes firm, a part and allows the agonist to work more efficiently. E.g. when you do a push-up, the agonists are the elbow extensor muscles. The abdominal muscles act as stabilizers to keep the trunk straight, while the arms move the trunk up and down 6. Neutralizer - If a mm can do two (or more) actions, but only one is wanted, a neutralizer contracts to prevent the unwanted motion. E.g. the biceps flexs the elbow & supinate the forearm. For attainment of pure F, the pronator teres contracts to counteract the supination component of the biceps muscle 7. A synergist - is a mm that works with one or more other muscles to enhance a particular motion e.g.?? 2.7 Factors affecting force production The magnitude of the force produced by a muscle is dependent on several factors such as : 1. Fiber Type 25 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2. % Fiber Recruitment 3. Fiber Architecture 4. Number of Muscle Fibers 5. Angle of Pull 6. Muscle Temperature 7. Rate of Stimulation 8. Force-velocity Relationship 9. Elastic Properties 2.7.1 Type of muscle fibers The inherent fibre type determines the force produced as illustrated in Table 2 below: 2.7.2 Number of mm fibers * The more muscle fibers one possesses the more force production they create * Largely genetically pre-disposed * Increase in cross-sectional area of muscle fiber will increase force production 26 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.7.3 Rate of Stimulation * The faster the rate of stimulation the more force production * Based on the “All or None Principle”: twitch → summation → tetanus 27 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.7.4 Percentage of Fiber Recruitment Largely dependent on the resistive forces that the muscle deals with slow twitch (ST) fibers have a lower activation threshold than fast twitch (FT) fibers As the speed and force requirement of the muscle increases more FT fibers are activated 2.7.5 Force-Velocity Relationship * As speed of contraction increases force production decreases and vice-versa * Force-Velocity Curve 2.7.6 Fiber Architecture Fusiform or Parallel – specializes in greater ROM and speed of ROM Pennate – specializes in greater force production (contains greater # of fibers w/n a cross sectional area) 2.7.7 Muscle Temperature Warm muscles will result in: ↑ elasticity of muscles ↑ conduction velocity (↑ rate of stimulation) ↓ internal friction 28 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2.7.8 Proportional Length of Muscle 2.7.9 Angle of Pull Two important functions of muscle contraction: 1. Rotation of the bone segment 2. Stabilization of the bone segment * Near 90 degrees of pull the muscle work best to rotate the joint * As it goes away from 90 degrees it works more towards joint stability 29 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 3 MODULE 3: NEUROMUSCULAR CONTROL OF MOVEMENT – INTRODUCTION 3.1 Module outline 1. Levels of integration of the control of movement in the nervous system 2. The muscle spindle 3. Facilitatory and inhibitory influences on the final common pathway 3.2 Introduction 30 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 31 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 3.3 Overview of relevant neuroanatomy and neurophysiology 3.3.1 Cerebellum This structure contains more neurons than the rest of the brain It receives input from the spinal cord, the sensory systems, and from the cortex. Functions are: 1. co-ordinates muscle activity 2. maintains balance 3. plays a role in motor skill learning clinical e.g. of a condition in which the cerebellum is affected is cerebral palsy in Cerebral Palsy : 1. Mvts becomes jerky, erratic & uncoordinated 2. Mvt sequencing becomes problematic 3. Altered speech 4. Manual dexterity affected 3.3.2 Basal Ganglia This comprises a set of interconnected nuclei in the forebrain which includes: 1. Caudate nucleus 2. Globus pallidus 3. Substantia nigra 4. Subthalamic nucleus 5. Putamen The caudate nucleus and putamen receive sensory input from the thalamus and corte while the globus pallidus sends informatio to the primary motor cortex via the thalamus The BG have rich connections to the cerebral cortex and subcortical nuclei 32 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 They not only contribute to mvt but they also influence cognitive functioning CLINICAL - Damage to them produces a variety of changes in movement though two main problems emerge: Akinesia (an absence of spontaneous movement) as seen in Parkinson’s disease. Hyperkinesia (rapid involuntary movements) e.g. athetoid CP 3.3.3 Reticular formation This consists of a large number of nuclei located in the core of the medulla, pons and midbrain which principally control muscle tone and posture Nuclei in the pons and medulla also control automatic movements such as vomiting, coughing and sneezing 33 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 3.3.4 Cerebral Cortex The CC does not connect directly to the muscles, but sends axons to the medulla and spinal cord, which in turn send axons to the muscles responsible for the overall planning of movements & not individual mm contractions It is not responsible for automatic and involuntary movements e.g. coughing There are several cortical regions controlling various aspects of movement: Primary motor cortex: The main movement processing region, within which separate areas control different parts of the body Premotor cortex: Active during the preparations before a movement has begun (motor planning). Supplementary motor area: Active during the preparation before a rapid series of voluntary movements. Prefrontal cortex: Responds mostly to sensory signals that lead to movement. Somatosensory cortex: Primary receiving area for touch and is closely connected with the motor processing regions and spinal cord CLINICAL -Cerebral Cortex Symptoms of CC lesions correlate with site of lesion of the CC E.g. lesions to primary motor cortex (e.g. from a stroke) result in loss of voluntary movements on the contralateral (opposite) side of the body damage to the supplementary motor area leads to Apraxia Apraxia is a specific loss of the ability to plan and correctly perform co-ordinated motor skills 34 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 3.3.5 Reflex arc The reflex arc governs the operation of reflexes Nerve impulses follow nerve pathways as they travel through the nervous system 35 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 3.3.5.1 Components of the reflex arc Component Function Receptor – detects the stimulus sensitive to a specific type of internal or external change Sensory neuron – conveys the sensory info. to transmit nerve impulses from the receptor into the brain or brain or spinal cord spinal cord Interneuron: relay neurons. serves as processing center, conducts nerve impulses from the sensory neuron to a motor neuron Motor neuron: conduct motor output to the transmits nerve impulse from the brain or spinal cord out to Periphery an effecter Effector: can be a muscle or gland Response to stimulation by the motor neuron and produces the reflex or behavioral arc 3.3.5.2 Summary of the reflex arc 36 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 3.3.6 The Alpha Motor Neuron Innervates skeletal muscle Receives input from higher centers Receives sensory input from muscle stretch and tension receptors 3.4 Muscle spindle sensory receptors within the belly of a mm , which primarily detect changes in the length of this mm Are composed of a few intrafusal muscle fibers that lack actin and myosin in their central regions are non-contractile, & serve as receptive surfaces 37 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 concentrated primarily in muscle belly between the fibers sensitive to stretch & rate of stretch Insert into connective tissue within muscle & run parallel with muscle fibers Spindle number varies depending upon level of control needed e.g. greater concentration in hands than thigh 38 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 3.4.1 Mechanism of action Stretching the muscles activates the muscle spindle - there is an increased rate of action potential in Ia fibers Contracting the muscle reduces tension on the muscle spindle- there is a decreased rate of action potential on Ia fibers 3.5 Golgi Tendon Organ (GTO) Stretch Receptor Free nerve endings found inside connective tissue capsule Respond to stretch and contraction Activated Golgi tendon organ inhibits alpha motor neurons i.e. Decreases muscle contraction 39 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 3.5.1 Summary of mechanism of action of GTO 3.6 Control of movement 40 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 Mvt is reflexive and voluntary in nature Reflexively controlled & Supraspinally (higher centre) controlled There are 3 levels of control i.e. 1. Spinal cord 2. Brain stem & cerebellum 3. Cerebral cortex & BG There are 3 steps in making a mvt i.e. : 1. Decision making and planning 2. Initiating movement 3. Executing movement 3.6.1 Reflex movement Control Least complex Spinal integration Modulated by higher brain centers Postural reflexes Receive continuous sensory input from visual, vestibular & mms Integrated in the brain stem 41 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 3.6.2 Voluntary movement Most complex Cerebral cortex integration Can become involuntary/rhythmic (After initiation becomes reflexive) e.g. riding a bicycle rhythmic mvts are a combination of reflex and voluntary actions Initiated and terminated by input from cerebral cortex Mvts integrated by the CNS 42 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 4 MODULE 4: MECHANICAL PROPERTIES OF BIOLOGICAL TISSUE 4.1 Module outline Stress/ strain Elastic modulus, stiffness of matter Lubrication Viscoelasticity 4.2 Introduction Biological Tissues are unique in that they exhibit the following characteristics: * Anisotropic * Viscoelastic * Organic – they self-repair & adapt to changes in mechanical demand 4.3 Important terminology Load – the sum of all the external forces and moments acting on the body or system Deformation – local changes of shape within a body Inhomogeneous – this is when a material consists of two or more different structural components e.g. CT has two primary components: a cellular component and an extracellular matrix Anisotropic- as biological tissues are inhomogeneous, this affects the loading response ,this is the direction-dependent response to force application 4.4 Strength of Biological Materials * The strength of biological materials is defined by the ability of the material to withstand stress without failure * The strength of a material is affected by: 1. Microstructure 2. Age 3. Fluid content 4. Type, direction and velocity of loading 43 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 4.5 Load-deformation relationship 4.5.1 Type of loading deformation is changes in shape experienced by a tissue or structure when it is subjected to various loads NB – the effects of forces ( can change - speed, direction & shape of an object) Deformation depends on the angle of application of the force as well as the magnitude of the applied force (resolution of forces) The extent of deformation dependent on: 1. Size and shape (geometry) 2. Material – Structure – Environmental factors (temperature, humidity) – Nutrition – Load application – Magnitude, direction, and duration of applied force – Point of application (location) – Rate of force application – Frequency of load application – Variability of magnitude of force 44 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 4.6 Structural vs. Material Properties Structural Properties Material Properties Load-deformation relationships of like tissues Stress-strain relationships of different tissues Structural properties refer to mechanical properties that a structure possesses due to its size & geometry However, the material in “like” structures (e.g., two bones such as the tibia and femur) can vary enough to result in different load-deformation relationships that are due to material differences as well as structural differences Material properties refers to mechanical properties that a material or tissue possesses due to the make-up the tissue (the content as well as the arrangement of fibers & cells) Stress & strain represent normalized loads & deformations, therefore, making differences between tissues primarily due to differences in the material itself, and not differences in the structure Therefore what’s the diff btwn stress & strain & how are they related?? 45 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 4.7 Stress –strain relationship 4.7.1 Stress = F/A (N/m2 or Pa) stress - is force applied per unit area, where area is measured in the plane that is perpendicular to force vector 4.7.2 Strain ∆𝐿 is the change in length (amount of deformation) 𝐿_𝑜 is the original length = dimension/original dimension Strain is dimensionless it quantifies the % of deformation caused by the applied stress. change in shape of a tissue relative to its initial shape 46 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 4.7.3 Young’s modulus * Young’s modulus is a measure of the material’s resistance to deformation * Young’s modulus quantifies how much stress is required to generate a give strain * It does not depend upon the size or shape of the object, but only the material the object is composed of * e.g. Copper has a modulus of 120 x 109 Pa & Steel has a modulus of 200 x 109 Pa , thus, steel is more resistant to deformation than is copper 4.7.4 Relationship between strain & stress “Stress is what is done to an object; strain is how the object responds” Stress and Strain are proportional to each other for elastic materials according to Hooke’s Law According to Hooke’s Law , modulus of elasticity = stress/strain NB- Modulus of elasticity is constant for a specific substance (up to a certain point) as illustrated in the fig. below : 4.7.5 Typical load-deformation curve 47 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 4.8 Typical Stress-Strain Curve 4.8.1 Concept 1: Elastic & plastic regions Elastic region – tissue behaves like an ideal spring; response is linear, according to Hooke’s law (force described by F=kx) Plastic region – response is non-linear, slope of curve changes; structure of tissue is altered; permanent changes in tissue (plastic region) 48 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 4.8.2 Concept 2: Stiffness (elastic modulus) Stiffness/elastic modulus/ young’s modulus/modulus of elasticity= /) Hooke’s law (posits that stress and strain are linearly related – only true for biological tissues when the magnitude of the stretch is relatively small Linear response at low loads Different materials have different stiffness as depicted in differences in Young’s Modulus as illustrated below: The slope of the elastic portion of the curve represents the stiffness of the tissue Tissues A & B have the same stiffness than Tissue C, and the stiffness of A & B is greater than that for Tissue C This greater stiffness means that at a given load, A and B do not deform as much as C For example, at a load of For example, when a load of 10 N is applied to Tissues A and B, they are deformed ~2.5 cm. The same load applied to Tissue C causes a deformation of almost 6 cm Therefore, Tissues A and B are stiffer (more resistant to deformation) than Tissue C 49 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 4.8.3 Concept 3: Yield point The point at which the curve begins to bend is the point at which permanent damage is sustained in the tissue Prior to this point, the tissue is said to be elastic At the point that permanent damage occurs (the yield point), the tissue is said to become plastic, meaning that it will not be able to perfectly regain its shape These yield points would define the point at which a ligament sprain occurs The load at which this yield point occurs would be defined as the tissue’s strength Therefore, the strength for Tissue A is ~20 N, and the strength for Tissues B and C is ~15 N. 4.9 Tissue mechanical properties Mechanical tissues possess the following properties : 1. Extensibility 4. Strength 7. Malleability 2. Elasticity 5. Ductility 8. Toughness 3. Stiffness 6. Brittleness 9. Resilience 10. Hardness 1. Elasticity the ability of a material to resume its original size and shape upon removal of applied loads 50 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 2. Extensibility can determined frm a T/l curve Tissue A can be deformed ~5 cm before suffering permanent damage & tissue C can be deformed almost 9 cm before suffering permanent damage Therefore, Tissue C is the most extensible of these three tissue For example, ligaments and tendons may have equal strengths [i.e., be able to handle equals loads before suffering permanent damage (say 100 N], but at this load, the tendon may deform more than the ligament, which means that the ligament is stiffer than the tendon. 3. Ductility Ductility – characteristic of a material that undergoes considerable plastic deformation under tensile load before rupture High %elongation in high ductile material 4. Brittleness Brittleness – absence of any plastic deformation prior to failure Fails suddenly without warning No yield point Rupture strength = ultimate strength 5. Malleability characteristic of a material that undergoes considerable plastic deformation under compressive load before rupture Ductile materials are often malleable 51 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 6. Resilience Property of a material enabling it to endure high impact loads without inducing a stress in excess of the elastic limit Resilience – measure of energy absorbed by a material and returned when load is removed; materials that quickly return to their original shape are called resilient Energy is absorbed during blow is stored and recovered when body is unloaded Measured by area under elastic portion of curve 7. Toughness Toughness – property of a material enabling it to endure high-impact or shock loads ability to absorb energy during plastic deformation; & a measure of the capacity of a material to sustain permanent deformation If material can be highly stressed & greatly deformed without rupture, it is tough Area under the curve (1 tougher than 2) Brittle materials are not very tough (small plastic deformation before fracture occurs) 52 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 4.10 Viscoelasticity * When an elastic material containing fluid is deformed the return of the material to its original shape is time delayed * Viscoelastic materials exhibit both an elastic response and viscous damping * Bones, tendons, ligaments, cartilage, muscle, and skin are all viscoelastic * Viscoelastic materials display both a time dependent and rate dependent response The mechanical response of a viscoelastic material are time and velocity dependent Viscoelastic materials exhibit: 1. a creep response 2. a force relaxation response 4.10.1 Creep * Creep is a time dependent response of viscoelastic tissues * The muscle-tendon complex is loaded with a weight * When the load is initially applied the muscle undergoes deformation * Following this initial deformation the muscle continues to deform at a much lower rate, this later deformation is creep 53 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 4.10.2 Force- relaxation * Force relaxation is a time dependent response of viscoelastic tissues * When the muscle is stretched the force (resistance to stretch) rises rapidly * Then when the stretch is held the force (resistance to stretch) slowly declines over time, this is force relaxation 4.11 Applied biomechanics of biological tissues * As mentioned earlier, biological tissue is inhomogeneous this is illustrated in the diagram below: 54 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS) PHYSIOTHERAPY & OCCUPATIONAL THERAPY 2: 2021-22 * The differences in biological tissue are accounted by the variability in type & quantity of cells, and differences in the amount of structural proteins as illustrated below: * The differences in the structural proteins is outline in the fig below: 4.12 Mechanical properties of bone tissue 4.12.1 Introduction Bone tissue possesses the following properties: 1. Heterogeneous/Nonhomogeneous 4. Stiff 2. Anisotropic 5. Tough 3. Strong 6. Little elasticity 55 KINESIOLOGY – BIOMECHANICS HANDBOOK for Bsc (HONS
