Biomechanical Principles PDF

Biomechanical Principles Created by Hung Bui, D.C. Objectives 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Define the 3 Newton’s laws Understand Newton’s Law in linear and rotational motions Define different types of forces Understand the effect of force on skeletal system Differentiate center of mass vs....

Biomechanical Principles Created by Hung Bui, D.C. Objectives 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Define the 3 Newton’s laws Understand Newton’s Law in linear and rotational motions Define different types of forces Understand the effect of force on skeletal system Differentiate center of mass vs. center of gravity Understand the relationship b/t BOS and LOG Define different types of loads Explain stress and strain curves Understand musculoskeletal torques Understand viscoelasticity and its properties Explain different types of contractions Define 3 lever systems and its mechanical advantage Newton’s 1st Laws of Motion Newton’s basic laws and principles of mechanics form the foundation for understanding human movement. First Law–the Law of Inertia: an object will remain at rest or in uniform motion unless acted on by an external force. – Static equilibrium–remains motionless (velocity is zero) when acted on by forces. – Dynamic equilibrium–remains in constant motion (constant velocity which is not zero) when acted on by forces (rare in the human body) https://qph.ec.quoracdn.net/main-qimg-01ce69382ddd630aaccc7a712d71819a-c Newton’s 2nd Laws of Motion Second Law–the Law of Acceleration: the acceleration of an object is proportional to the net forces acting on it and inversely proportional to its mass -> F=ma – i.e., the greater the mass of an object the more force it takes to move it. https://kaiserscience.files.wordpress.com/2015/08/newtons-laws-of-motion-11-728.jpg Newton’s 3rd Laws of Motion Third Law–the Law of Reaction: for every action there is an equal and opposite reaction. http://slideplayer.com/6008745/20/images/3/Newton%E2%80%99s+third+law+Examples%3A.jpg Newton’s Laws: Linear Vs. Rotational Motions Linear Motion 1st: Law of Inertia: – A body remains at rest or in constant linear velocity except when compelled by an external force to change it state Rotational Motion – A body remains at rest or in constant angular velocity about an axis of rotation unless when compelled by an external torque to change it state https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSxeOTZ43LpkxglDB4-6Z96xBT1vQHWJmvUblji0OMxVQ_UX8qy8A Newton’s Laws: Linear Vs. Rotational Motions Linear Motion 2nd: Law of Acceleration: – The linear acceleration of a body is directly proportional to the force causing it, takes place in the same direction in which the force acts, and is inversely proportional to the mass of the body Rotational Motion – The angular acceleration of a body is directly proportional to the torque causing it, takes place in the same rotary direction in which the torque acts, and is inversely proportional to the mass moment of inertia of the body http://slideplayer.com/4773342/15/images/42/9.3+Rotation+and+Newton+s+2nd+Law.jpg Newton’s Laws: Linear Vs. Rotational Motions Linear Motion 3rd: Law of ActionReaction: – For every force there is an equal and opposite directed force Rotational Motion – For every torque there is an equal and opposite directed torque. https://www.healthproductsexpress.com/13100-cart_default/15137709-15137709-Wrist-Arm-ResistanceExercise-Bar-Cando-Twist-N-Bend-Bar-Green-Medium.jpg Tissue Slack & Line of Drive In manual therapies, e.g. chiropractic, when we prepare to assess or manipulate a joint of the body we address tissue slack & line of drive. Tissue Slack: is the resultant vector applied to the skin before palpation or adjustment of the joint. Line of Drive: is the resultant vector of force applied to the joint during palpation or adjustment of the joint. – Example: The tissue slack & line of drive for a particular thoracic adjustment may be verbalized as Inferior to Superior (I-S), Medial to Lateral (M-L), and Posterior to Anterior (P-A), but the actual procedure is performed using the resultant vector a.k.a.: I-S, M-L & P-A Introduction to Kinesiology & Biomechanics FAB101 Kinematics Translation vs. Rotation Kinetics Arthrokinematics *Planes of Motion *Typical Joint Morphology *Type of forces *Movements b/t Joint Surface *Impact of Forces on Musculoskeletal Tissues *Muscle’s Action at a Joint * Close vs. Loose Packed Positions *Internal and External Forces *Terminology of Action of Muscles *Axis of Rotation *Degrees of Freedom *A Matter of Perspective Musculoskeletal Forces Musculoskeletal Torques Muscle and Joint Interaction Osteokinematics *Types of Muscle Activation Musculoskeletal Levers *Three Classes of Levers *Mechanical Advantage Kinetics Kinetics: A branch of mechanics that describes the effect of forces on the body or the musculoskeletal system. push or pull forces that can produce, arrest, or modify movement. Forces provide the ultimate stimulus for movement and stabilization of the body – Newton’s Second Law: Force = mass x acceleration Given a constant mass, a force is directly proportional to the acceleration of the mass. Musculoskeletal Forces Types of forces Impact of forces on the musculoskeletal system Internal and external forces Types of forces Distraction forces–a net force that moves an object (bony segment) away from an adjacent object (bony segment). Tensile forces–forces that create opposite pulls on an object; opposite forces are necessary to create tension. (ligaments and joint capsules) Gravitational forces–the result of gravity on an object. Contact forces–reaction forces resulting from the push of one object against another; a.k.a. joint reaction forces when it involves two contiguous joint surfaces Compression forces–two forces that go in opposite directions toward each other. https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSB8c2dDWdGWgRDhiCgKA9tlZx425hcI8BhGPgAFYu2cVlSEQDZPA Center of Mass Vs. Center of Gravity Center of mass (CoM) is the point at the exact center of an object’s. – CoM is not changed as changing in position Center of Gravity (CoG): can be defined as a point in a body or system around which its mass or weight is evenly distributed or balanced and through which the gravitational force acts on – Location of CoG is variable and generally depends on body position. CoG is the same as CoM when considering the weight of the mass. – Weight is the gravitational force acting on a mass. (W = mg) CoG is found anterior to the S2 tubercle in the human body (lowering the CoG over the base of support increases stability; raising it decreases stability) – i.e. punching bag toy, palm tree https://physicsoftkd.files.wordpress.com/2016/02/center-of-mass.jpg?w=660 http://karatecoaching.com/wp-content/uploads/2013/10/centre-of-gravity.1.jpg Base of Support (BoS) The area which supports the mass above Line of Gravity (LoG) When the Line of Gravity (LoG) of an object falls outside of its Base of Support (BoS), the object will fall over. The closer to the edge of the BoS that the LoG gets, the less stable the object is. The closer to the middle of the BoS that the LoG gets, the more stable the object becomes. Introduction to Kinesiology & Biomechanics FAB101 Kinematics Translation vs. Rotation Kinetics Arthrokinematics *Planes of Motion *Typical Joint Morphology *Type of forces *Movements b/t Joint Surface *Impact of Forces on Musculoskeletal Tissues *Muscle’s Action at a Joint * Close vs. Loose Packed Positions *Internal and External Forces *Terminology of Action of Muscles *Axis of Rotation *Degrees of Freedom *A Matter of Perspective Musculoskeletal Forces Musculoskeletal Torques Muscle and Joint Interaction Osteokinematics *Types of Muscle Activation Musculoskeletal Levers *Three Classes of Levers *Mechanical Advantage Impact of Forces On The Musculoskeletal System Load-a force that acts on the body. Forces or loads that move, fixate or stabilize the body also have the potential to deform and injure the body. Stress-internal resistance generated as a ligament resists deformation , divided by its cross-sectional area. (force per unit of cross-sectional material.) Strain-material deformation resulting from stress. Example: % increase in a ligament’s stretched length relative to its original length. Stiffness-The ratio of stress caused by an applied strain in a tissue (ligament) is a measure of the tissue’s stiffness. All normal connective tissues exhibit some degree of stiffness. – Clinical term “Tightness” implies an abnormally high stiffness. The Stress-Strain Curve Non linear (Toe) region– slack is removed with minimal force Elastic region–the structure returns to its original dimensions when force is removed Yield point–between elastic & plastic regions (end of elastic limit) Plastic region–deformation is permanent Ultimate failure point– material fails under load Types of Load Tension-creates tensile stress & strain Compression-creates compressive stress & strain Bending–Combined tension and compression Shear-the result of parallel equal forces in opposite directions Torsion-the result of forces applies perpendicular to the long axis of a structure Combined Loading-Torsion and compression Bending forces on bones– combined tensile and compression stresses & strains Tissues are weakened by disease, trauma, overuse or disuse may not be able to resist certain loads. Example: fracture of the proximal femur by a fall or strong muscle contraction in a hip weakened by osteoporosis. Viscoelasticity Viscoelasticity–is the property of materials that exhibit sensitivity to rate of loading or deformation. All structures in the human body are viscoelastic.  Viscosity -a material’s ability to dampen shearing-forces  Elasticity -a material’s ability to recover after deformation Properties of viscoelastic materials: 1. 2. 3. 4. 5. Creep: progressive strain of a material when exposed to a constant load over time.  The original form is regained after the load is removed (reversible);  Example: Creep explains why you are taller in the morning than at night. Constant compression by body weight on the spine squeezes fluid out of the discs. Fluid is reabsorbed at night while non-weight-bearing. Relaxation: the decrease in stress in a deformed structure with time when the deformation is held constant Hysteresis: the loss of energy during a loading cycle, even though the material may return to its original form (difference b/t energy expended and energy regained) Fatigue: the process of formation and propagation of cracks in a structure subjected to repetitive load cycles. The applied load is generally below the failure load of the structure Damping: the property of a material that constitutes resistance to speed General Connective Tissue Properties Some definitions related to connective tissue property: 1. Brittle materials such as bones which do not have plastic region, undergo little deformation before failure. 2. Ductile materials such as muscles, ligaments and tendons, undergo considerable deformation before failure. 3. Resilience: ability to absorb and store energy within the elastic range and release that energy to return to its original dimension immediately following the removal of load. i.e. tendon stretches, stores energy, releases energy 4. Toughness: reflects the material’s resistance to failure or ability to absorb large amount of energy prior to failure. General Connective Tissue Properties Bone –can withstand significantly greater compressive forces than tensile forces before failure. Tendons –good tensile strength; – a reduction in tensile forces (immobilization) leads to atrophy, especially at the musculotendinous junction; Ligaments –similar to tendons; less tensile strength but can handle a wide range of load directions better than tendons; – immobilization leads to atrophy; – much longer recovery time than for tendons (up to 1 year) Cartilage –responds well to compressive forces & recovers rapidly due to fluid exudation & imbibitions. Connective Tissue Failure Rupture –failure, tearing & disruption of connective tissue fibers; usually tendons, ligaments & other soft tissue structures Avulsion –tearing off of a bony attachment Fracture –a failure of bony tissue Joint Sprains (ligament injury) Grade I –only a few fibers are involved; good chance of tissue recovery Grade II –more fibers involved & partial tearing; does not completely recover. Grade III –complete rupture; no chance of recovery; possible bone involvement. Spiral Fracture Dislocated elbow Finger Dislocations –DIP & PIP Introduction to Kinesiology & Biomechanics FAB101 Kinematics Translation vs. Rotation Kinetics Muscle and Joint Interaction Arthrokinematics *Planes of Motion *Typical Joint Morphology *Type of forces *Movements b/t Joint Surface *Impact of Forces on Musculoskeletal Tissues *Muscle’s Action at a Joint * Close vs. Loose Packed Positions *Internal and External Forces *Terminology of Action of Muscles *Axis of Rotation *Degrees of Freedom *A Matter of Perspective Musculoskeletal Forces Musculoskeletal Torques Osteokinematics *Types of Muscle Activation Musculoskeletal Levers *Three Classes of Levers *Mechanical Advantage Internal and External Forces Internal Forces-produced from structures within the body. – Active-generated by muscle – Passive-generated by tension in stretched connective tissue (ligaments or tendons) External Forces–produced by forces acting from outside the body. – Gravity, lifting free-weights, carrying luggage etc. Vector-a quantity that is specified by its magnitude and direction (i.e. velocity). Typically depicted by an arrow in a drawing. A scalar has a magnitude, but no direction (i.e. mass or speed of an object). A vector should have: – – – – Magnitude: the length of shaft of arrow Direction: spatial orientation of the arrow Sense: orientation of the arrowhead Point of application: where the base of the vector contacts the part of the body Length and Tension Curve of Muscle https://andersnedergaard.dk/wp-content/uploads/2013/02/LengthTensionMuscle.png Musculoskeletal Torques Forces exerted on a body can have two outcomes: Can Translate a bony segment-Push or pull an object in a linear direction Can Rotate a bony segment-if the force is applied at some distance perpendicular to the axis of rotation. Moment Arm–The shortest distance between the axis of rotation of the joint and force. Torque-the product of a force and its moment arm produces a torque or a moment. The rotatory equivalent of a force. Leverage-the moment arm length possessed by a particular force. Internal and external torques are constantly competing for dominance across joints in the body. The more dominant torque is reflected by the direction of movement or position of joints at any given time. (Think of how this is obvious in patients with poor posture) Musculoskeletal Torques https://qph.fs.quoracdn.net/main-qimg-9128804038683013bde6393d67fe2b08 Introduction to Kinesiology & Biomechanics FAB101 Kinematics Translation vs. Rotation Kinetics Muscle and Joint Interaction Arthrokinematics *Planes of Motion *Typical Joint Morphology *Type of forces *Movements b/t Joint Surface *Impact of Forces on Musculoskeletal Tissues *Muscle’s Action at a Joint * Close vs. Loose Packed Positions *Internal and External Forces *Terminology of Action of Muscles *Axis of Rotation *Degrees of Freedom *A Matter of Perspective Musculoskeletal Forces Musculoskeletal Torques Osteokinematics *Types of Muscle Activation Musculoskeletal Levers *Three Classes of Levers *Mechanical Advantage Muscle and Joint Interaction A muscle produces a force through three type of activation (contraction): 1. Isometric activation: occurs when a muscle is producing a force while maintaining a constant length 2. Concentric activation: occurs as a muscle produces a force as it shortens 3. Eccentric activation: occurs as a muscle produces an active force while being elongated Notice: 2 &3 a.k.a isotonic contraction (activation) https://image.slidesharecdn.com/chapter9section5-140204174807-phpapp02/95/section-5-chapter-9-types-of-muscle-contractions9-638.jpg?cb=1391536191 Muscle and Joint Interaction Muscle’s action at a joint can cause a torque in a particular rotation direction 1. Flexion and Extension: around the X-axis in the sagittal plane 2. Lateral Flexion: around the Z-axis in the coronal plane 3. Rotation: around the Y-axis in the transverse plane Musculoskeletal Levers There are 3 types of musculoskeletal levers: 1. First-Class Lever: Axis of rotation positioned b/t the opposing forces i.e. head and neck extensor muscles E I E I https://alexeinstein.files.wordpress.com/2014/09/lever1.jpg Musculoskeletal Levers 2. Second-Class Lever: Axis of rotation is located at one end of the bones and the internal force possesses greater leverage than external force (i.e. a calf muscle group). This lever is rare in human body. I E I E https://alexeinstein.files.wordpress.com/2014/09/lever2.jpg Musculoskeletal Levers 3. Third-Class Lever: Axis of rotation is located at one end of the bones and the external force possesses greater leverage than internal force i.e. biceps brachii muscle in elbow). I I E E This lever system is the most common in human body. https://alexeinstein.files.wordpress.com/2014/09/lever3.jpg Musculoskeletal Levers Mechanical advantage (MA): is the ratio (FI)/(FE) of internal movement arm (FI) and external movement arm (FE) – 1st class levers may have a MA less than 1, equal to 1, or greater than1 – 2nd class levers always have a MA more the 1 – 3rd class levers always have a MA less than 1 I E E I I E http://www.angelfire.com/la/Ivan/images/3rd.jpg References Kinesiology of the Musculoskeletal System: Foundation for Rehabilitation, 2nd ed. or 3rd ed., chapter 1 & 4 by DA Neumann. Levangie PK & Norkin CC., editors. Joint Structure and Function, A Comprehensive Analysis, chapter 2, 3th edition. FA Davis Co., Philadelphia, 2011. The End