PT PAP 101- Force and Gravity Systems (GMU)

PT PAP 101- FORCE SYSTEMS September 10, 2024 www.gmu.ac.ae COLLEGE OF ALLIED HEALTH SEIENCES Objectives At the end of this Lecture, the student should be able to Define...

PT PAP 101- FORCE SYSTEMS September 10, 2024 www.gmu.ac.ae COLLEGE OF ALLIED HEALTH SEIENCES Objectives At the end of this Lecture, the student should be able to Define force Explain Mechanobiology Define Newtons law of Motion Explain Different types of force systems. Describe the implications of force systems in the human body. Explain Anatomic pulleys and its implications in human body. Understand angle of muscle pull  Mechanobiology It is the study of how cells sense the mechanical forces of the physical microenvironment and what molecular cascades and cellular responses ensue when they are sensed. Mechanobiology may greatly facilitate the development of new therapies that control mechanical forces and thereby specifically induce desired molecular, cellular, tissue, and/or organ formation, changes, or repair” in rehabilitation science.  Force Force is that which pushes or pulls through direct mechanical contact or through the force of gravity to alter the motion of an object Internal forces are muscle forces that act on various structure of the body External forces are those outside the body Weight, gravity, air or water resistance, friction, or forces of other objects acting on the body  NEWTON’S LAW Law of Acceleration It states that the acceleration of an object is proportional to the unbalanced forces acting on it and inversely proportional to the mass of that object a=F/m Law of Equilibrium It states that an object will remain at rest or in uniform motion unless acted on by an unbalanced force Law of Reaction For every action there is an equal and opposite reaction  Linear Force System Linear force system exists whenever two or more forces act on the same object and in the same direction, line or plane All forces act along the same action line  Concurrent Force System Forces applied to an object may not be in a line but have action lines that lie at angles to each other Two or more forces acting at a common point of application but in different (divergent) directions/angle. Composition of Forces: Net effect of these two divergent forces is called the Resultant force, and appears to occur at the common point or at the point of intersection and found out through the process known as composition of forces RF Man A and B are pulling the block each at right angels with a force of 75lb each Action lines AB- A on block and BB-B on block are in different directions but are commonly applied through the COG of the block  The net effect or resultant of the two pulls will be in a line that lies between the men Vector AB and BB are drawn to scale maintaining a 90 angle between them Line AB' and BB' are drawn parallel to AB and BB forming a polygon The resultant force R lies at the intersection of AB and BB and its action line and magnitude are drawn so that the arrow head lies at the intersection of lines AB' and BB'  Linear force system Cervical Traction-Linear force Psoas major and iliacus muscles act along the same action line, point of application, and same direction- Linear force Trapezius muscle on both sides act along the same action line, but in opposite directions. 11  Concurrent force system Action of sternal and clavicular parts of the pectoralis major 12  Application in Human Body Divergent muscle pulls : Concepts of concurrent force system can be used to determine the resultant of two or more segments of one muscle or two muscles when they have a common attachment Example: Deltoid consists of AD,PD,MD Anterior portion of the deltoid muscle –AD Posterior portion of the deltoid muscle -PD acting on the humerus AD & PD form the polygon  R is the resultant force vector (AD & PD) for the above polygon R represents the sum of AD and PD The deltoid is composed of the middle segment MD R and MD coincide and the common point of application they are part of the same linear force system The resultant in a linear force system is the arithmetic sum of vectors R and MD Vector Fms produces abduction of the Fms=R+MD arm  Pectoralis major – sternal & clavicular portion CPM = Clavicular portion of PM SPM = Sternal portion of PM Fms = Net force or resultant which brings about adduction and medial rotation of humerus  Parallel force system When all the forces are coplanar (acting at the same plane), at two different points, and parallel to each other, but do not share the same action line Hamstring muscles components: medial (semitendinosus & semimembranosus) and lateral (biceps femoris) 16  Force of Friction 1. Friction may exist on an object whenever 2 objects touch each other. 2. Shear force is a force that is applied parallel to contacting surfaces in the direction of the attempted movements. 3. Friction has magnitude only when there is a shear force applied to an object; that is friction has magnitude only when 2 contacting objects move or attempt to move on each other 4. The action line of friction forces always lies parallel to the contacting surfaces 5. The direction of the force of friction is always opposite to the direction of the movement 19  Use of friction in physiotherapy Moving patient in bed Massage Suspension therapy Sit to stand on mat 20 21  PT- PAP 101-Gravity September 17, 2024 www.gmu.ac.ae COLLEGE OF ALLIED HEALTH SEIENCES Objectives At the end of this lesson, the student should be able to Define Gravity Correlate gravity forces on human movements Describe Segmental COG Understand what is Equilibrium Explain the Rules of Equilibrium  Introduction Gravity is an external force acting under normal circumstances which affects all the objects The first external force to be considered acting on human body Force of gravity is the pull of earth on a body or its segments and it’s a consistent one. Described as mutual attraction between the earth and an object Gravitational force is always directed towards the centre of earth which is towards the ground Gravity- Vector Gravity being a force is a vector quantity Point of application: COG Line of application: Centre of mass of object Direction : Towards centre of the earth Magnitude: Equal to Gravitational Force  Center of Gravity Although gravity acts at all COG is an hypothetical point points on an object or segment of at which all mass would an object, its application is given appear to be concentrated as Centre of Gravity (COG) and is the point at which the Center of Gravity is also referred force of gravity would as centre of Mass appear to act.  Symmetry and COG In a symmetrical object the In a asymmetrical object the COG will be located at the COG will be located geometric center of the towards the heavier end object where all the mass is evenly distributed around that point  COG in Human Body- s2 Segmental Whole When segments are combined, Each segment in body is gravity acting on combined segments acted on by the force of can be represented by a single COG gravity and has its own COG  COG in Human Body- s2 When the trunk is inclined forward, location of new COG lies outside the body Location of COG varies with each of the many and varied postures the body assumes  Line of Gravity The line of gravity is an imaginary vertical line from the centre of gravity to the ground or surface the object or person is on. It is the direction that gravity is acting upon the person or object. Gravity vector is commonly referred to as the Line of Gravity (LOG) LOG can best be visualized as a string with a weight on the end (a plumb line) with the string attached to the COG of an object Line of gravity  Positions and COG When the posture is good the LOG passes through the mid cervical and mid lumbar vertebrae and in front of thoracic vertebrae  Base of Support Base as applied to a rigid body is the area by which it is supported and in contact with the supporting surface In lying position posterior aspect of the whole body forms the base In stride standing BOS is an area as wide as the feet and as long as the distance between their outer borders Different types of walking aids are used to increase BOS of patients  Equilibrium Static equilibrium is a state where bodies are at rest; dynamic equilibrium is a state where bodies are moving at a constant velocity (rectilinear motion). In both cases the sum of the forces acting on them is zero. Equilibrium results when the forces acting upon a body are perfectly balanced.  Rule of Equilibrium The condition of equilibrium is most stable if, 1.The larger the BOS of an object, the greater the stability of that object 2.The closer the COG of the object is to the BOS, the more stable is the object. 3.An object cannot be stable unless its LOG falls within its BOS 4.Greater the mass of the object greater the stability 5.Greater the friction between the supporting surface and the BOS, the more stable the body will be.  Stability and COG For an object to be stable the LOG must fall with in the base of support (BOS) When LOG falls outside the BOS the object will fall(less stable) When BOS of an object is large, The LOG has more freedom to move with out passing beyond the limits of the base Examples………………………………… When a man stands with his legs spread apart,the base is larger side to side and the trunk can move a good deal in that plane with out displacing the LOG from COG When a person grasps or leans on another object that object can become part of BOS  When COG is low, movement of the object in space is less likely to cause the COG & LOG to fall outside the BOS The longer the LOG, the higher the COG, the less stable the object The shorter the LOG, the lower the COG, the more stable the object Relocation of Centre of Gravity Location of COG of a body depends not only on the arrangement of segments in space but also on the distribution of mass of the object Most common way to functionally redistribute mass in the body is to add external mass Every time we add an object to the body by wearing it,carrying it or using it the new COG for the combined body & the external mass will shift toward the additional weight;the shift will be proportional to the weight added 1. Results in shifting the COG down and to the right 2. Because his COG is now lower, he is theoretically more stable 3. Though he is standing only on one leg addition of crutches enlarges the base of support and thus improves the stability Holding a heavy suit case in right hand??? Results in shift of the COG up and to the right Because the LOG would move toward the right foot the man leans to the left to compensate Man leans laterally to the left not to relocate the COG but to bring the LOG back to the middle of base of support  PT PAP 101- Torque/Moment Arm, Composition of Forces & Mechanical Advantage of Levers October 22, 2019 www.gmu.ac.ae COLLEGE OF ALLIED HEALTH SEIENCES Objectives At the end of this Lecture, the student should be able to Define Torque and Moment arm Analyze the composition of forces acting in a human body Define Mechanical advantage Explain the Mechanical Advantage of all the force systems.  Torque ▪ Torque is the amount of force needed by a muscle contraction to cause rotatory joint motion ▪ Torque (T) is a product of the magnitude of applied force (F) and the distance (r) that force lies from the axis of rotation, θ (moment arm) is the angle between the force vector and lever arm. Typically, it is equal to 90° ▪ T= rFsin(θ)  Moment Arm ▪ The [MA] Movement arm of any force vector will always be the length of a line that is perpendicular to the force vector and intersects the joint axis. ▪ The length of the Moment arm always relates to the angle of application of force. ▪ Lever Arm[LA]: It is the distance from the axis to the point at which a force is applied to the lever Moment Arm of a Muscle Force  Moment arm of Gravity ✔ The gravity acts vertically downward, the angle of application of gravity changes as the segments moves in space ✔ The force of gravity will be applied perpendicular to a segment whenever the segment is parallel to the ground ✔ When a body lever is parallel to the ground, gravity acting on that segment exerts its maximum torque Fms of Biceps & Gravity 1.The MA of any force is greatest when the action line is applied at 90ᶿ to its lever or when the action line is as close to 90ᶿ as possible 2. Resistance arm created by gravity on COG at the point of application Composition of forces Torque = Force X perpendicular distance or =Force X Moment Arm Net force acting while flexing the elbow If biceps is contracting (EF) with a force of 120lb applied at a distance (EA) 1 inch from the axis. Weight of forearm/hand segment(R) is 10lb and COG lies 10inch(RA) from the axis TEF = (F) (EA) TR = (F) (RA) TEF =(120lb)(1in) TR =(10lb)(10in) TEF =120inlb TR =100inlb ▪ Biceps exerts a torque of 120 in-lb on the forearm in a counterclockwise or positive direction TEF = +120in-lb ▪ Torque exerted by gravity is in clockwise or negative direction TR = –100in-lb ▪ Net rotation of a lever can be determined by finding the sum of all the torques acting on the lever ▪ If the sum of all torque is zero, the torques are balanced and the lever will not rotate ▪ When the torque of biceps is +120in-lb and the torque of gravity is – 100in-lb, resultant torque is 20 in-lb in a counter clockwise direction-flexion of forearm & hand Analysis of forces while extending elbow with weight in the hand There are three forces acting i.muscle force of biceps on forearm at its attachment (Fms=120lb) ii.force of gravity on forearm at the COG (G=10lb) iii.weight of the ball (WH=5lb)  Calculation Lever arms for these forces are 1,10,15 in We can find the net torque acting on the lever by finding the sum of the torques created by each force Torque exerted by biceps on the forearm in a counterclockwise/positive direction T Fms= (+ 120lb)×(1in) = +120in-lb Torque exerted by gravity on fore arm is in clockwise/negative direction TG = (− 10lb)×(10in) = −100in-lb Torque exerted by weight is clockwise /negative direction TWH = (− 5lb)×(15in) = −75in-lb  Net rotation of a lever can be determined by finding the sum of all the torques acting on the lever Net torque T= TFms + TG + TWH (+120in-lb)+(−100in-lb) +(−75in-lb) = −55in-lb  Types of muscle contraction and Levers ✔When an active muscle shortens -concentric contraction, it must be moving the segment under consideration in the direction of its pull so that the muscle will be the effort force ✔When an active muscle lengthens-eccentric contraction it must be pulling in a direction opposite to motion of the segment under consideration so that the muscle will be acting as resistance force ✔When a lever is in rotational equilibrium muscles acting on the segment under consideration are neither shortening nor lengthening- isometric contraction.  Terminologies to know ✓ Effort force force that is causing the rotation of the lever ✓ Resistance force force that is opposing the rotation of the lever ✓ Fulcrum Axis or the point where the rotation occurs E F R ✓ Effort Arm [EA] it refers specifically the distance of the lever EA RA arm from the effort force to the axis ✓ Resistance Arm[RA] it refers specifically the distance of the lever arm from the resistance force to the axis ✓ Torque the ability of any force to cause rotation of the lever  Lever principle It is the ratio of the length of the lever on the applied effort side of the fulcrum to the length of the lever on the load force side of the fulcrum. MA= DE : DL Mechanical advantage refers to how much a simple machine multiplies an applied force. The location of the effort, load, and fulcrum will determine the type of lever and the amount of mechanical advantage the machine has. Mechanical Advantage= Effort Arm [1.2] Resistance Arm [Effort arm >Load arm] Mechanical Advantage Levers are used to multiply force, In other words, using a lever gives you greater force or power than the effort you put in. In a lever, if the distance from the effort to the fulcrum is longer than the distance from the load to the fulcrum, this gives a greater mechanical advantage  Levers 1st order Lever: MA>1 2nd Order lever : Effort moves far than Load MA>1(Easy to lift) 3rd Order lever: Load moves far than Effort , MA< 1(Hard to lift, but the object moves more)- Uses more force to lift  First Class Levers This exists whenever 2 parallel forces are applied on either side of the axis at some distance from the axis, creating rotation of the lever in opposite direction  Second class levers This exists whenever two parallel forces are applied at some distance from the axis, with the resistance force applied closer to the axis than the effort force Third class levers This exists whenever 2 parallel forces on a lever are applied so that the effort force lies closer to the axis of the lever than does the resistance 23  Connective tissue October 21, 2024 www.gmu.ac.ae COLLEGE OF ALLIED HEALTH SEIENCES Learning Objectives By the completion of this topic, student will be able 1.Identify the properties of the connective tissues 2.Understand load deformation curve of connective tissue 3. Know the stress-strain curve of bone/ligament/tendon  Connective tissue It is a term given to several different tissues of the body that serve to connect, support and help bind other tissues in the body.  Connective tissue Classification Loose connective tissue works to hold organs in place and is made up of extracellular matrix and collagenous, elastic and reticular fibers. Dense connective tissue is what makes up tendons and ligaments and consist of a higher density of collagen fibers. Specialized connective tissues are adipose tissue, cartilage, bone, blood, and lymph. Although connective tissue is diverse, all connective tissue consists of three main components: Ground substance Fibers Cells  Ground substance Ground substance is an amorphous sticky material that has a high water content and fills the spaces between cells and fibers, basically forming a gel. It consists of large molecules termed glycosoaminoglycans (GAGs) which link together to forming yet larger molecules called proteoglycans.(Adipose tissue/Bone) This leads to the extracellular matrix being very effective in being resistant compressive forces  Fibres The fibroblasts secrete the connective tissue fibers. The three types of connective tissue fibers are: Collagen fibers - most are type I collagen (most abundant protein in the body). Tensile strength - resistance to stretching Elastic fibers - contain elastin and fibrillin. Elasticity - can be stretched, yet still, return to its original length Reticular fibers - contain type III collagen. Their function is supportive, form a supporting network in the reticular lamina of the basement membrane found in soft tissues such as the liver, bone marrow, spleen, and lymph nodes  Cells Bone contains Osteocytes, and osteoblasts which secrete the type of ECM that makes up bone. Cartilage contains chondrocytes and chondroblasts which secrete the type of ECM found in cartilage, respectively. Blood vessels contain Endothelial cells and present underneath the epithelium of blood capillaries, are cells called Pericytes, which can divide and provide a source of new fibroblasts, especially following tissue injury  Connective tissue & functions Resistance to stretch and tear Structural support Insulation Storage of body fuels A medium for intercellular exchange  Young's modulus Resistance force by an object to the external force is known as modulus of elasticity or young modulus. tension or compression.. Modulus of elasticity vary for different materials. If the slope of curve is steep, modulus of elasticity will be high, compliance low. Ex. Bone If the slope of curve is gradual, modulus of elasticity will be low, High compliance. Ex. Subcutaneous fat.  Stress strain and loading Stress Is acting upon a cross sectional area of a material Stress=Force applied/Area [Mega pascals] Strain: % of change in length on material in response to load application Type of stress a tissue undergoes  Stress on bone The stress-strain curve obtained by loading a sample of compact bone in tension. E is the stiffness of the material (Young's modulus for modelled isotropic materials)  Stress strain on tendon/ligament Typical stress-strain curve for mammalian tendon. Three regions are shown: (1) toe region (2) linear region, and (3) failure region https://youtu.be/11qu6BX_jNg https://youtu.be/glcO_0gPad4 https://youtu.be/WkVpOHBO90E  TISSUE HOMEOSTASIS Many clinical issues can be related to a disruption of the local tissue’s homeostasis due to exposure to stress beyond its adaptive ability.  TISSUE HOMEOSTASIS Loads above this threshold will cause tissue damage at a higher rate than to which it can adapt; loads below will result in a detraining effect. Healthy individuals have a fairly wide gap between the minimal effective dose and the maximum tolerated dose. With injury, this zone narrows and it requires more precise dosage to stay within the continuum of function. The rehabilitation goal is to increase these envelope borders by driving its upper limits to the right. Manual loading Tissue repair , flow dynamics and adaptability are highly dependent on the type of mechanical forces applied during treatment. These forces are called manual loading Two types Tension loading Compression loading Tension loading In tension loading forces are applied in opposite direction causing tissue to elongate Used in lengthening shortened tissue and break excessive cross links. Traction longitudinal and cross fiber stretching and are examples of tendon loading Compression loading Forces are applied into tissue often to the center Under compression loading the tissue will shorten and widen increase the pressure within the tissue and affecting fluid flow Compression is therefore a very useful pump like technique to facilitate the flow of fluid  Reference DeryaÖzer Kaya , Architecture of tendon and ligament and their adaptation to pathological conditions; Comparative Kinesiology of the Human Body, 2020, Pages 115-147