Biomechanics PDF

PTY1016 Foundation of Physiotherapy: Movement Biomechanics Basic Concepts of Mechanics of Biological Tissues Alan Wong, PhD, MPH [email protected] Kinetic Concepts Forces Gravity Muscles Externally ap...

PTY1016 Foundation of Physiotherapy: Movement Biomechanics Basic Concepts of Mechanics of Biological Tissues Alan Wong, PhD, MPH [email protected] Kinetic Concepts Forces Gravity Muscles Externally applied resistances Friction Types of Forces on Musculoskeletal System The manner by which forces or loads are most frequently applied to the musculoskeletal system is shown. The combined loading of torsion and compression is also illustrated. Neumann, D. A. (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier. Basic Mechanics Concepts – (1) Stress Stress (σ) is a physical quantity. The stress is the force per unit area applied to the material. Basic Mechanics Concepts – (2) Strain Stresses lead to strain (or deformation). Putting pressure on an object causes it to stretch. Strain is a measure of how much an object is being stretched. Stress and Strain Elastic Modulus Stress divided by strain is defined as the modulus of elasticity an indicator of an object's likelihood to deform when a force is applied. Page 17 Basic Mechanics Concepts – Stress-Strain Curves Ref: Nihat Özkaya and Margareta Nordin. Fundamentals of Biomechanics: Equilibrium, Motion, and Deformation. 2nd ed. Springer; 1999. Tensile Stress-Strain Response There are 3 distinct regions in the stress- strain curve: Initial linearly elastic region where slope = elastic modulus (E). Intermediate region – exhibit yielding & nonlinear elasto- plastic material behaviour. Final region – exhibits linear plasticity where slope = strain hardening modulus. In biological tissues: Dunleavy, K., & Kubo Slowik, A. (2019). Therapeutic exercise prescription. Elsevier, chapter 1. In biological tissues: Dunleavy, K., & Kubo Slowik, A. (2019). Therapeutic exercise prescription. Elsevier, chapter 1. Stress-strain Relationship The stress-strain relationship of an excised ligament that has been stretched to a point of mechanical failure (disruption). Neumann, D. A. (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier. Viscoelasticity All connective tissues are viscoelastic materials, i.e. fluid-like component to their behaviour Viscosity – material's resistance to flow (a fluid property) High-viscosity fluids (e.g., honey) flow slowly. Lower-viscosity fluids (e.g., water) flow quickly. Decreases with temperature and slowly applied loads Elasticity – material’s ability to return to its original length or shape after the removal of deforming load. Length changes or deformations are proportional to applied forces/loads. Depend on connective tissue’s collagen and elastin content and organization. When stretched, work is done (= force x distance) and energy in stretched material increases. Oatis, C. A. (2016). Kinesiology: The Mechanics and Pathomechanics of Human Movement. (3rd ed.). New York: Wolters Kluwer. Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Time- and rate-dependent properties Viscoelastic materials deform under either tensile or compressive forces, but return to their original state after removal of the force Creep Stress-relaxation Strain-rate sensitivity Hysteresis Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis.  Time- and rate-dependent properties of dense connective tissues. A. Creep: When the tissue is loaded to a fixed force level, and length is measured, the latter increases with time (T0 to T1) and the tissue recovers its original length in a nonlinear manner (T1 to T0). (From Oskaya N, Nordin M: Fundamentals of Biomechanics, Equilibrium Motion and Deformation [ed. 2]. New York, Springer-Verlag, 1999, with permission from the publisher as well as the author, Margarita Nordin.) Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Creep Progressive strain (deformation) of a material when under a constant load over time. A phenomenon of viscoelasticity, and therefore common in human tissue. What are some examples for clinical practice?  Time- and rate-dependent properties of dense connective tissues. B. Force or stress-relaxation: If the tissue is stretched to a fixed length and held there, the force needed to maintain this length will decrease with time. (From Oskaya N, Nordin M: Fundamentals of Biomechanics, Equilibrium Motion and Deformation [ed. 2]. New York, Springer-Verlag, 1999, with permission from the publisher as well as the author, Margarita Nordin.) Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Stress Relaxation Stress relaxation is the reduction of stress within a material over time as the material is subjected to a constant deformation. When applying and maintaining a fixed displacement, or strain, the resisting force (from which stress is calculated) can be measured as a function of time. Stress generally decreases with time and hence the label “relaxation.”  Both creep and stress relaxation are important behaviors in biological soft tissue.  What are some examples of stress relaxation in human movement?  Time- and rate-dependent properties of dense connective tissues. C. Hysteresis: As the tissue is loaded and unloaded, some energy is dissipated through tissue elongation and heat release. (From Oskaya N, Nordin M: Fundamentals of Biomechanics, Equilibrium Motion and Deformation [ed. 2]. New York, Springer-Verlag, 1999, with permission from the publisher as well as the author, Margarita Nordin.) Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Hysteresis When force is applied (loaded) and removed (unloaded) to a structure, the resulting load- deformation curves do not follow the same path. Not all of the energy gained as a result of the lengthening work (force x distance) is recovered during the exchange from energy to shortening work. Some energy is lost, usually as heat.  Time- and rate-dependent properties of dense connective tissues. D. If the tissue is loaded rapidly, more energy (force or stress) is required to deform the tissue. (From Oskaya N, Nordin M: Fundamentals of Biomechanics, Equilibrium Motion and Deformation [ed. 2]. New York, Springer- Verlag, 1999, with permission from the publisher as well as the author, Margarita Nordin.) Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Strain-rate sensitivity Most tissues behave differently if loaded at different rates. When a load is applied rapidly, the tissue is stiffer, and a larger peak force can be applied to the tissue than if the load was applied slowly. The subsequent stress-relaxation also will be larger than if the load was applied slowly. Creep will take longer to occur under conditions of rapid loading. What are some examples of clinical applications? Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. PTY1016 Foundation of Physiotherapy: Movement Biomechanics Biomechanics of the Bone, Joint and Soft Tissues Alan Wong, PhD, MPH, BPhty(Hons) [email protected] Biological Tissues Biological tissues can be classified as : Hard – e.g. bone, teeth. Soft – Tendons, ligaments, joint capsules, skin, muscles, articular cartilage. Page Fracture Bone fractures heal by forming bone callus at the site of fracture. When a bone is fractured, blood pours into the injured area to form a clot. This is known as a fracture haematoma and its role is to act as a provisional scaffold for migration of cells and a source of growth factors released by the haematopoietic cells trapped in the haematoma. These growth factors induce the migration and proliferation of osteoblasts, fibroblasts and mesenchymal cells, which form a type of granulation tissue around each fracture end, thus forming a bridge between the separated ends. In the first week of injury, the granulation tissue gives rise to islands of cartilaginous procallus, also known as soft callus , to anchor the broken ends together. Within two to three weeks, through a process known as endochondral ossification, the soft callus is slowly converted to a hard bony framework to further stabilise the connection between the separated ends. Between four to 16 weeks, the callus is remodelled so that the cartilaginous structure converts to calcified bone matrix and the bone is shaped to return towards the near-normal shape and function, including clear separation of the medullary cavity from the compact bone. The most important factors that influence bone healing include blood supply, mechanical stability, the location of the injury and bone loss due to age-associated changes or the extent of trauma to the bone. Patient diet also has an impact on the quality of formed bone; for example, nutritional deficiencies in calcium and vitamin D or loss of capacity to absorb calcium through procedures such as gastric bypass. Medication prescribed, such as bisphosphonates, also affects a patient's Tomkins, Z. (2020). Applied Anatomy & Physiology : an interdisciplinary approach. capacity to generate good-quality bone. Elsevier, pp. 279-304. Bone Tissue Bone is the primary structural element of the human body Supports and protects the internal organ. Assists movement: Sites for muscle attachment Facilitates muscle actions and body movement Mineral “bank”: Reservoir for calcium deposit to maintain homeostasis of blood calcium Blood cell production: Hemopoiesis (red marrow) Energy storage: Adipose tissue (yellow marrow) Page Types of the Bones Patton, K. T., & Thibodeau, G. A. (2019). Anatomy & physiology ([Adapted International edition].). Elsevier, chapter 11. Long Bone Patton, K. T., & Thibodeau, G. A. (2019). Anatomy & physiology ([Adapted International edition].). Elsevier, chapter 11. Flat and other bones Patton, K. T., & Thibodeau, G. A. (2019). Anatomy & physiology ([Adapted International edition].). Elsevier, chapter 11. Composition of the Bone Biologically, bone is a connective tissue which binds together various structure of the body. Mechanically, bone is a composite material with various solid and fluid phases. Bone contains inorganic components which makes it hard and rigid and organic components which provide the flexibility. https://in.pinterest.com/pin/773000723516028291/ Composition of the Bone There are two types of bone tissue: Cortical or compact bone tissue is a dense material forming outer shell (cortex) of bones. Cancellous, trabecular, or spongy bone tissue consists of thin plates (trabeculae) in a loose mesh structure enclosed by the cortical bone. Bones are surrounded by a dense fibrous membrane called the periosteum and covers entire bone except for the joint surfaces which are covered by articular cartilage. Spongy Bone vs. Compact Bone: What's the Difference? https://www.pinterest.com/pin/718676053017868345/ Mechanical Properties of the Bone Major factors influencing mechanical behavior of bone: Composition of bone. Mechanical properties of tissues comprising the bone. Size and geometry of bone. Direction, magnitude, and the rate of applied loads. Page 33 Mechanical Properties of the Bone Bone can be characterised as: Nonhomogeneous material as it consists of various cells, organic and inorganic substances with different material properties. Anisotropic (direction dependent) as material properties is different when acted upon in different directions. Viscoelastic (time and rate dependent), e.g., bone can resist rapidly applied load much better than slowly applied loads. Hence, bone is stiffer and stronger at higher strain rates. Page 34 Effects of Anisotropy Stress-strain behavior is dependent on orientation of bone with respect to direction of loading. Page 35 Effects of Anisotropy Table: Mechanical properties for cortical bone Example: Cortical bone Loading Mode Ultimate Strength Has larger ultimate strength (MPa) (ie stronger) and a larger Longitudinal elastic modulus (ie stiffer) in Tension 133 the longitudinal than Compression 193 Transverse transverse direction. Tension 51 Also, it is more brittle (w/o Compression 133 yielding) as compared to bone ELASTIC MODULI, E specimens loaded in longitudinal Longitudinal 17.0GPa direction. Transverse 11.5GPa SHEAR MODULUS,G 3.3GPa An experiment to demonstrate Anisotropic behavior Viscoelastic Property of the Bone Page 25 Comparison of Mechanical Properties Between Cortical and Cancellous Bones Structural Integrity of the Bone Factors affecting integrity of bone: Osteoporosis reduces bone integrity in terms of strength and stiffness by reducing apparent density. Surgery altering normal bone geometry. Bone defects. Screw holes for pins & bone plates can cause stress concentrations on bone. Bone fracture occurs when stresses generated in bone exceeds the ultimate strength of bone. Osteoporosis Osteoporosis is the most epidemic bone disease in older populations. It is characterized by: low bone mass, deterioration of bone micro-architecture, compromised bone strength. It leads to bone fragility and increased risk of fracture under low loads. Biomechanics of Soft Tissues Page 29 Musculoskeletal Soft Tissues Types of soft tissues Articular Cartilage Tendon Ligament Muscle Joint Capsules Skin Others Composition of the Soft Tissues All soft tissues are composite materials. Collagen and elastin fibers made up the main structural elements of soft tissues. Collagen Fibers Collagen fibres are not effective under compression. When stretched, energy is stored in the fiber like a spring. When release, energy returns to the fiber to its unstretched state. Individual fibrils of the collagen fibers are surrounded by a gel-like ground substance, which consists mainly of water. Collagen fibre possesses a two-phase, solid-fluid, or viscoelastic material behavior. Elastin Fibres The noncollagenous tissue components include: Elastin which is another fibrous protein whose material properties resemble the properties of rubber. Elastin and microfibrils form the elastic fibres that are highly extensible and reversible even at high strains. Elastin fibres possess a low-modulus elastic material property, while collagen fibres show a higher-modulus viscoelastic behavior. Collagen vs Elastin Collagen Elastin Found in skin and protective tissue. Found in the connective tissue of elastic structures. 3rd most abundant protein in the body. Less abundant. Generally white. Generally yellow. Gives strength to structures. Provides elasticity to structures. Produced until the ageing process begins. Produced mainly in the fetal period. Viscoelastic Behavior of Biological Tissues In general, the mechanical behavior of biological tissues can be described as viscoelastic. A viscoelastic model comprises: A spring to model the elastic behavior, and A dashpot to model the time dependent behavior. Biomechanics of Muscles and Joints Page 36 Skeletal Muscles Movement of human body segments is achieved as a result of forces generated by skeletal muscles which convert chemical energy into mechanical work. The skeletal muscle is composed of muscle fibres and myofibrils. Muscles exhibit viscoelastic material behaviour. Muscles are viscous in the sense that there is an internal resistance to motion. Muscle Contraction Contraction is a unique ability of the muscle tissue, which is defined as the development of tension in the muscle. In engineering mechanics, contraction implies shortening under compressive forces. In muscle mechanics, contraction can occur as a result of muscle shortening or muscle lengthening, or it can occur without any change in the muscle length. There are various types of muscle contractions: concentric, eccentric and isometric contractions. Skeletal Joints The human body is both: Rigid in the sense that it can maintain a posture. Flexible in the sense that it can change its posture and move. The flexibility of the human body is due primarily to the joints, or articulations, of the skeletal system. The primary functions of joints: Mobility Stability Classification of Joints Skeletal Joint Classification: Structural Skeletal Joint Classification: Functional Synar-throdial joints (immovable): formed by two tightly fitting bones and do not allow any relative motion of the bones forming them (eg skull). Amphiar-throdial joints (slightly movable): allow slight relative motions, and feature an intervening substance (a cartilaginous or ligamentous tissue) whose presence eliminates direct bone-to-bone contact (eg vertebrae). Diar-throdial joints (freely movable): Varying degrees of relative motion Articular cavities Ligamentous capsules Synovial membranes and fluids Types of Synovial Joints Types of Synovial Joints Examples Glenohumeral joint (ball-and-socket) enables the arm to move in all three planes (triaxial motion): High level of mobility Reduced stability Increase vulnerability of the joint to injuries, such as dislocations. Humeroulnar joint: movement only in one plane (uniaxial motion) more stable Less prone to injuries than the shoulder joint. The extreme case of increased stability is achieved at joints that permit no relative motion between the bones constituting the joint. The contacting surfaces of the bones in the skull are typical examples of such joints. Function of the Articular Cartilage Covers the articulating surfaces of bones at the diarthrodial (synovial) joints. Provides weight bearing surface with low friction and wear. Facilitates the relative movement of articulating bones. Distributes loads over larger contact area due to compliant nature, ie reduces stress applied to bones. Loads acting on the Articular Cartilage During daily activities, articular cartilage is subjected to tensile, shear and compressive stresses. Under tension, cartilage responds by realigning the collagen fibers which carry the tensile loads applied to the tissue. Shear stresses on the articular cartilage are due to frictional forces between the relative movement of articulating surfaces. However, coefficient of friction for synovial joint is very low (about 0.001 – 0.06) and has insignificant effect on the stress resultants. Lifespan Changes of the Joints Joint stiffness in older people. Fibrous joints change first. Changes in symphysis joints may also over in vertebral column (water loss from intervertebral discs) -> loss of disc height and flexibility. Synovial joint loses elasticity. Reduced physical activity may lead to disuse and poor circulation. Importance of regular physical activity and exercises to keep joints functional. Biomechanics of Tendons and Ligaments Page 49 Tendons and Ligaments Tendons and ligaments are fibrous connective tissues. Tendons execute joint motion by transmitting mechanical forces (tensions) from muscles to bones. Unlike muscles, tendons & ligaments are passive tissues, ie. cannot contract to generate forces. Tendons Compared to muscles, tendons are stiffer, have higher tensile strengths, and can endure larger stresses. At joints where space is limited, muscle attachments are via tendons. Enable muscles to transmit forces to bones without wasting energy to stretch tendons. Ligaments Attach articulating bones to one another across a joint. Guide and stabilise skeletal joint movement. Prevent excessive motion. Greater proportion of elastic fibers which account for higher extensibility but lower strength and stiffness. It is also viscoelastic and exhibits hysteresis. Magee, D. J. (2014). Orthopedic physical assessment (Sixth edition.). Elsevier. Comparison of Tendons and Ligaments https://differences.info/tendon-vs-ligament/ Summary Biomechanical principles are foundational to our understanding, description and analysis of human movements. Kinematic is concerned with the description of the movement in terms of time and spatial factors; kinetics is concerned with the forces involved in bringing about the movement. Both linear and angular (rotatory) movements can be interpreted in terms of its kinematics and kinetics. Newton’s laws can be applied in the analysis of human movements; concepts of mass, inertia, displacements, speed and velocity, acceleration, momentum and impulse are important in describing and analyzing movements. Forces acting on the human body can be analyzed and resolved using polygon or parallelogram methods. Human body can be conceptualized in terms of machines, e.g. lever and pulley. Centre of gravity, centre of mass and base of support are central to our understanding of the human body in equilibrium. PTY1016 Foundation of Physiotherapy 1: Movement Biomechanics Seah Jianxing [email protected] References Dutton, M. (2020). Dutton’s introduction to physical therapy and patient skills (Second edition.). McGraw Hill. Chapter 3 https://accessphysiotherapy.mhmedical.com/content.aspx?bookid=2976&sectionid=250229067#1176134695 Biomechanics of the body. (2008). Video Education Australasia. https://singaporetech.primo.exlibrisgroup.com/permalink/65SIT_INST/1i4buil/alma991000741070204056 https://fod-infobase-com.eu1.proxy.openathens.net/p_ViewVideo.aspx?xtid=129227 Nordin, M., & Frankel, V. (2012). Basic biomechanics of the musculoskeletal system (4th ed., International ed.). Wolters Kluwer Health/Lippincott Williams & Wilkins. https://singaporetech.primo.exlibrisgroup.com/permalink/65SIT_INST/1vcvbdp/alma991000504529704056 Neumann, D. A., Kelly, E. R., Kiefer, C. L., Martens, K., & Grosz, C. M. (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier. Chapter 4, pp 77-114 https://singaporetech.primo.exlibrisgroup.com/permalink/65SIT_INST/1i4buil/alma991000614999804056 Hall, S. (2017). Basic Biomechanics. In Basic Biomechanics (8th ed.). McGraw-Hill Education LLC. https://singaporetech.primo.exlibrisgroup.com/permalink/65SIT_INST/1qe4ih4/cdi_mcgrawhill_accessphysiotherapy_sc n00360082 Richards, J. (2018). The comprehensive textbook of clinical biomechanics (2nd edition.). Elsevier. https://singaporetech.primo.exlibrisgroup.com/permalink/65SIT_INST/1i4buil/alma991000694999404056  Figure 1. Model of elastic energy storage Arm-cocking and acceleration phases of the overhand throw (A). Humans (left) and chimpanzees (right) differ in arm abduction and elbow flexion during throwing (B) because of differences in shoulder orientation, which alters the major line of action of the Pectoralis major (C). Aligning the long axis of the humerus with the major axis of P. major and flexing the elbow maximizes inertia to shoulder flexion torque and loads the elastic ligaments in the shoulder. However, chimpanzee morphology is compromised between maximizing humeral rotation or elbow extension. Signatures of shoulder orientation found in the scapula (D) can be used to reconstruct hominin shoulder orientation. Roach, N. T., Venkadesan, M., Rainbow, M. J., & Lieberman, D. E. (2013). Elastic energy storage in the shoulder and the evolution of high-speed throwing in Homo. Nature, 498(7455), 483-486. https://www.bbc.com/news/science-environment-23061016 Why study biomechanics? Provides foundational understanding of mechanical principles and how they can be applied in analyzing human movement. Address problems related to human health, healthcare and performance. Even at a basic level of analysis, this information can be used to guide treatment decisions and to understand mechanisms of injury. Who apply biomechanics? Physiotherapists Podiatrists Biomedical engineers Personal trainer / instructor /coaches Orthopaedic surgeons Sub-branches of biomechanics Statics: study of systems in constant motion, including zero motion. Dynamics: study of systems subject to acceleration. Kinematics: study of the appearance or description of motion, mainly the time and spatial factors of motion. Kinetics: study of the actions of forces acting on a body that influence its movement. What is kinematics? What we visually observe of a body in motion is called the kinematics Shoulder horizontal abduction Shoulder extension of the movement. Kinematics is the study of the size, Shoulder internal rotation sequencing, and timing of movement, without regard for the forces that cause or result from the motion. Thi s Photo by Unknown Author i s licensed under CC BY-NC The kinematics of an exercise or a sport skill is known, more commonly, as form or technique.  Resultant muscle force Free body diagram of the shank-and-foot at the instant of heel contact during walking. The segment What is kinetics? Joint reaction force is isolated by figuratively “cutting through” the knee joint. Relevant forces are drawn in as shown. The X- Y coordinate reference frame is placed so the X axis Kinetics is the study is parallel with the shank. of forces, including internal forces Neumann, D. A., (muscle forces) and Weight of shank Weight of foot (2017). Kinesiology of the musculoskeletal external forces (the system : foundations for rehabilitation forces of gravity and Ground reaction force (Third edition.). Elsevier, pp. 84-85 the forces exchanged by bat and ball). Van Houwelingen, J., Schreven, S., Smeets, J. B., Clercx, H. J., & Beek, P. J. (2017). Effective propulsion in swimming: grasping the hydrodynamics of hand and arm movements. Journal of applied biomechanics, 33(1), 87-100. Kinematics vs Kinetics Kinematics Kinetics Distance, displacement, speed, Force, pressure, velocity, acceleration/deceleration torque, work, How far? How fast? How quickly? impulse, momentum, power Thi s Photo by Unknown Author i s licensed under CC BY Thi s Photo by Unknown Author i s licensed under CC BY Qualitative vs Quantitative Qualitative Quantitative For example: strong, skillful, agile, For example: flexible, fast running speed = 5 m/s height = 1.75 m mass = 68.2 kg Qualitative vs Quantitative Long jump: (Carl Lewis vs Mike Powell, 1991) Observer 1: Good jump, great lift. Observer 2: Carl Lewis – 8.91 metres, Mike Powell – 8.95 metres. Biomechanical researchers rely heavily on quantitative techniques to answer questions related to mechanics of living organisms. Physiotherapists, clinicians and coaches employ qualitative observations of their patients, athletes, or students to provide opinions and advice. https://www.youtube.com/watch?v=AxvDku19_IM How do we measure movements quantitatively? Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, pp. 104-106 Tools for Measuring Human Movement Quantities Videography Video of 30 pictures per second sufficient for most human movements. Clarity of the captured images. Number of cameras to use (to ensure all movements can be viewed and recorded). Movement Monitoring Systems Real-time tracking of reflective body markers (linked to computer for online calculation of kinematics/kinetics quantities). Goniometer or electrogoniometer Accelerometer Force plates – measures ground reaction forces. Electromyography (EMG) – measures muscle activities.  PTY1011 Foundation of Physiotherapy: Movement Biomechanics Kinematics of Human Movement Seah Jianxing [email protected] Kinematics vs Kinetics of movements (e.g. gait) Kinematics is the study of the geometry, pattern or form of motion with respect to time (not concerned with forces, but rather the details of the movement itself). Kinetics is the study of the forces associated with the motion. Knowledge of the patterns of the forces is necessary for an understanding of the cause of any https://www.tekscan.com/blog/medical/what-are-various-types- movement. gait-analysis Forms of Motion Most human movement is a combination of linear and angular motions. Linear motion: motion along a line, with all parts of the body moving in the same direction at the same speed (also: translatory motion or translation). Rectilinear: along a straight line. Curvilinear: along a curved line. Muscolino, J. E. (2017). Kinesiology : the skeletal system and muscle function (3rd edition.). Elsevier, chapter 18. Angular motion: rotation around a central imaginary line known as the axis of rotation, which is orientated perpendicular to the plane where the rotation occurs. Gymnast performs a circle on a bar. Springboard diver executes a somersault in midair. http://clipart-library.com/free/back-handspring-silhouette.html Spatial Reference Systems Spatial reference system used to standardize the measurements to be taken. Cartesian coordinate system: most commonly used. Movements primarily in a single direction, can be analyzed using a 2-dimensional Cartesian coordinate system (x - horizontal, y - vertical) 3-dimensional movement can be Nedeljković, Z., & Sekulić, A. (2015). Concept of spatial coordinate systems, their defining and implementation as a precondition in geospatial applications. Glasnik Srpsk og geografsk og analyzed by adding a z-axis. društva, 95(4), 77-102. Coordinate systems Cartesian coordinate system The rectangular or cartesian coordinate system that is composed of three mutually perpendicular directions (x,y,z) is the reference frame for describing linear movements. Polar coordinate system The polar coordinate system is suited for analyzing angular motions. As shown, the polar coordinate of point P2 are defined by parameters r and θ. r is the distance between the origin O of the coordinate frame and point P2, and θ is the angle line OP2 makes with the horizontal. 2 https://www.skillsyouneed.com/num/cartesian-coordinates.html Linear Kinematic Quantities Visually observable aspects of technique or form. The appearance of a motion. The pattern or sequencing of movement with respect to time. Linear Kinematic Quantities: Displacement What is linear displacement? Change in location Direct distance from initial to final location Vector equivalent of linear distance, i.e. direction is important, not just magnitude Measured in units of cm, m, km https://sciencestruck.com/difference-between-distance-displacement Linear Kinematic Quantities: Speed What is linear speed? Distance covered over the time taken Speed = A scalar quantity Measured in units of Linear Kinematic Quantities: Velocity What is linear velocity? velocity = Vector equivalent of linear speed Measured in units of Linear Kinematics: Resultant Velocity The resultant is the sum of two or more single vectors. Plane velocity + Wind velocity = Resultant velocity The velocity of a swimmer in a river is the vector sum of the velocities of swimmer and current.  The swimmer is swimming at speed 5 m/s north and the current velocity is 3 m/s east, what is the resultant velocity? Secondary school Maths revision: Pythagoras’ theorem a2 + b2 = c2 a c b 25 + 9 = 34; √34 = 5.8 m/s Linear Kinematic Quantities: Acceleration What is acceleration? Rate of change in linear velocity Acceleration = Measured in units of https://www.khanacademy.org/science/physics/one-dimensional- motion/acceleration-tutorial/a/acceleration-article  Increasing speed Increasing speed Negative acceleration Positive acceleration Decreasing speed Decreasing speed Positive acceleration Negative acceleration Motion in a negative direction Motion in a positive direction Acceleration may be positive, negative, or equal to zero, based on the direction of motion and the direction of the change in velocity. Is a soccer kick accelerating or decelerating? Thi s Photo by Unknown Author i s licensed under CC BY-NC-ND So far, we have been discussing linear kinematics. Let’s look at angular kinematics. Linear kinematics Angular kinematics Displacement (s) Angle (θ) Velocity (v) Angular velocity (ω) Acceleration (a) Angular acceleration (α) Thi s Photo by Unknown Author i s licensed under CC BY-SA Thi s Photo by Unknown Author i s licensed under CC BY-NC-ND Angular Kinematics – what types of angles? Absolute angle: Angle measured with reference to an absolute reference line, either horizontal or vertical. Relative angle: Angle at a joint formed between Also known as joint angle. longitudinal axes of adjacent body segments. The straight, fully extended position at a joint is regarded as zero degrees. Joint Angles Kim, J. H., & Won, B. H. (2019). Kinematic on Ankle and Knee Joint of Post-Stroke Elderly Patients by Wearing Newly Elastic Band-Type Ankle–Foot Orthosis in Gait. Clinical When a patient is in the interventions in aging, 14, 2097. anatomical position, all joint angles are zero degrees. This is used as the reference to determine joint angles. Relevance: in goniometry ROM measurements, consider the two segments about the joint the movement takes place to be in anatomical position, then you will know which is the joint angle. Joint Angles It is important that the body position does not influence the way the joint angles are measured/defined, so long the anatomical position is adopted as reference. Image source: https://www.youtube.com/watch?v=KZ40yziHPmY Ima ge source: http://voxmdweb.com/knee-exercises/active-range-motion-hip-flexion-supine-knee-bent/ Tools for Measuring Joint Angles Goniometer Essentially a protractor with two long arms attached. Direct measurement of relative joint angles on a human subject. One arm is fixed Other arm is free to rotate Center of goniometer is aligned over the joint center Two arms are aligned over the longitudinal axes Electrogoniometer Halo digital goniometer Angular Kinematics Angular kinematics – the description of the circular motion or rotation of a body / body segment. Motion is described in variables of: Angular distance (ϕ) and angular displacement (θ) Angular speed (σ) and angular velocity (ω) Angular acceleration (α) Angular Kinematics i. Angular distance (ϕ:phi) and angular displacement (θ: theta) Counterclockwise is positive Clockwise is negative [units: degrees, radians, or revolution (rev)] Initial A B Final C What is a Radian? The size of the angle subtended at the centre of a circle by an arc equal in length to the radius of the circle. Radian measure: radius radius 2 radians = 360o 1 radian Radians = Degrees (2) / 360 Radians = Degrees x  / 180 radius What are Radians? https://www.youtube.com/watch?v=cgPYLJ-s5II Units of angular measure 90 degrees 180 degrees 270 degrees  3 2 radians  radians 2 radians 1 1 3 revolution revolution revolution 4 2 4 Angular Kinematics ii. Angular speed (σ: sigma) Angular speed = Angular velocity (ω: omega) Angular velocity = [units: deg/s, rad/s, rev/s, rpm (revolution per minute)] Angular Kinematics iii. Angular acceleration (: alpha ) Question Cristiano Ronaldo kicks the soccer ball, the change in the angular velocity of the knee Angular acceleration = joint is 3.6 rad/s in 1.2 s, what is the angular acceleration of his knee? [units: deg/s2, rad/s2, rev/s2 ] Thi s Photo by Unknown Author i s licensed under CC BY-NC-ND  Relationships Between Linear and Angular Motion The larger the radius of rotation (r), the greater the curvilinear distance (s) traveled by a point on a rotating body. s2 s = r 2 2 where s is the curvilinear distance travelled, m s1 r is the radius of rotation, m 1 1  is the angular distance, radian  r2 r1 Relationships Between Linear and Angular Motion Since velocity is displacement over time, linear and angular velocity are related by the same factor that relates displacement: the radius of rotation (r). v = r where v is the linear (tangential) velocity, m/s r is the radius of rotation, m  is the angular velocity, rad/s Relationships Between Linear and Angular Motion The linear acceleration of a body in angular motion can be resolved into two perpendicular linear acceleration components. Tangential acceleration Radial acceleration at ar Tangential acceleration Component of acceleration of angular motion directed along a tangent to the path of motion. Represents change in linear velocity. 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑉𝑓 −𝑉 at = = at 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑡𝑖𝑚𝑒 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑡𝑖𝑚𝑒 r = = r 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑡𝑖𝑚𝑒 where at is the tangential acceleration, m/s2 v is the tangential velocity, m/s r is the radius of rotation, m  is the angular velocity, rad/s  Is the angular acceleration, rad/s2 Radial acceleration Component of acceleration of angular motion directed toward the centre of curvature. Represents change in direction. v2 ar = r = r 2 ar where ar is the radial (centripetal) acceleration, m/s2 v is the tangential velocity, m/s r is the radius of rotation, m  is the angular velocity, rad/s Relationships Between Linear and Angular Motion Tangential acceleration: 𝑉𝑓−𝑉𝑖 r𝑓 - ri at = = = r 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑡𝑖𝑚𝑒 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑡𝑖𝑚𝑒 at ar Radial or centripetal acceleration: a v2 ar = = r 2 r 2 2 Linear (total) acceleration: a = a t + a r Example A softball pitcher executes a pitch in 0.65 secs. If her pitching arm is 0.7 m long, what are the magnitudes of the tangential and radial accelerations on the ball just before ball release, when tangential ball speed is 20 m/s? What is the magnitude of the total acceleration on the ball at this point? Solution: at = (Vf – Vi) / t at = (20 – 0) / 0.65 = 30.8 m/s2 a ar = v2 / r = (20)2 / 0.7 = 571.4 m/s2 r = 0.7 m v = 20 m/s a=√ (30.8)2 + (571.4)2 = 572.2 m/s2 ar Levers and Pulleys Conceptualizing the human body as machines in terms of levers, wheel and axle and pulleys. Thi s Photo by Unknown Author i s licensed under CC BY-SA Thi s Photo by Unknown Author i s licensed under CC BY-SA Advantages of ‘machines’ Increases range of motion, e.g. levers. Provides speed, e.g. levers. Changes direction of applied force, e.g. pulleys. Increases magnitude of a force, i.e. less effort need to overcome load. Force to overcome resistance or load. Axis of movement. Resistance or load to be overcome. FAR 1st Class 2nd Class ARF 3rd Class AFR Houglum, P. A., & Bertoti, D. B. (2012). Brunnstrom's Clinical Kinesiology. (6th ed.). Philadelphia: F. A. Davis Company. Mechanical Advantage Mechanical advantage (MA) of a lever refers to the ratio between the length of the force arm and the length of the resistance arm. Assuming forces to be equal in magnitude… First-class lever: MA =/>/< 1 Second-class lever: MA > 1 (Advantage, less force need to lift huge weight, but lesser range of motion) Third-class lever: MA < 1 (Disadvantage, more force needed but more speed, larger range of motion) Most muscle systems are third class levers Pulleys Houglum, P. A., & Bertoti, D. B. (2012). Brunnstrom's Clinical Kinesiology. (6th ed.). Philadelphia: F. A. Davis Company.  A fixed pulley system changes direction of a force’s pull without providing any mechanical advantage. This may be useful clinically when it is desirable to create more or less force as a specific range of motion. Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Anatomical Pulleys Muscle fibres or tendons may wrap around a bone or are deflected by a bony prominence. Altering the direction of pull of a muscle is caused by the bone or bony prominence resulting in deflection or an anatomic pulley. Pulleys change the direction without changing the magnitude of the applied force. Change in action line produced by an anatomic pulley will have implications for the ability of the muscle to produce torque. Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. Anatomical Pulleys Levangie, P. K., & Norkin, C. C. (2011). Joint structure and function a comprehensive analysis. (5th ed.). Philadelphia: F.A. Davis. PTY1016 Foundation of Physiotherapy 1: Movement Biomechanics Kinetics of Human Movement Seah Jianxing [email protected] Kinematics vs Kinetics of movements (e.g. gait) Kinematics is the study of the geometry, pattern or form of motion with respect to time (not concerned with forces, but rather the details of the movement itself). Kinetics is the study of the forces associated with the motion. Knowledge of the patterns of the forces is necessary for an understanding https://www.tekscan.com/blog/medical/what-are-various-types- of the cause of any movement. gait-analysis Kinetic Concepts for Analyzing Human Motion Linear kinetics studies the causes of linear motion, while angular kinetics explains the causes of rotary motion. Basic Concepts Related to Kinetics Force is a push or a pull (product of mass and acceleration). Mass is the quantity of matter contained in an object. Inertia is the tendency of a body to maintain its current state of motion. Torque is the rotary effect of a force. Impulse is the product of the force and time over which the force acts. Linear Kinetics Newton’s Laws:Underlying Principles of Biomechanics Sir Isaac Newton (1687) Three Laws of Motion: 1. Inertia 2. Acceleration 3. Action-reaction Thi s Photo by Unknown Author i s licensed under CC BY Newton’s First Laws of Motion Law of Inertia: a body remains at rest or at a constant linear velocity except when compelled by an external force to change its state. Newton’s first law describes the case in which a body is in equilibrium (static or dynamic). Static equilibrium Dynamic equilibrium Newton’s Laws For example, a skater has a tendency to continue gliding with constant speed and direction because of inertia. Newton’s Second Laws of Motion Law of Acceleration: the acceleration of an object is directly proportionate to the amount of force applied and takes place in the direction in which the force is applied. Force is measured in newtons (N) Newton’s Third Laws of Motion Law of Action-Reaction: for every action, there is an equal and opposite reaction. When one body exerts a force on a second body, it exerts a reaction force that is equal in magnitude and opposite in direction of the first body. Law of Action-Reaction In accordance with the law of reaction, the weight of a box sitting on a table generates a reaction force by the table that is equal wt in magnitude and opposite in direction to the weight. R Law of Action-Reaction In accordance with Newton’s third law of motion, ground reaction forces are sustained with every footfall during walking/running. FV F FH Linear and angular (rotational) applications Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4. Steps in constructing a free body diagram Step I: Identify and isolate the free body under consideration. Step II: Establish a coordinate reference frame. Step III: Draw the internal (muscular) and external forces that act on the system. Step IV: Draw the joint reaction force. Step V: Write the governing equations of motion. A frontal plane depiction of a free body diagram isolating the system as a right arm and ball combination: resultant shoulder abductor muscle force (M); glenohumeral joint reaction force (J); segment weight (S); and ball weight (B). The axis of rotation is shown as an open red circle at the glenohumeral joint. The X-Y coordinate reference frame is placed so the X axis is parallel with the upper extremity. Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4. Mechanical Behavior of Bodies in Contact Linear momentum is defined as the vector quantity of motion that an object possesses (i.e., motion content of an object). The product of the mass and the velocity of an object. Momentum = mv [units: kg m/s] where m is the mass, v is the velocity. Thi s Photo by Unknown Author i s licensed under CC BY Which Has More Momentum? Large object Mass=100 kg Velocity= 10 m/s, east Small object Mass=10 kg Velocity= 100 m/s, east Conservation of momentum In the absence of external forces, the total momentum of a given system remains constant (does not change). M1 = M2 (mv)1 = (mv)2 Newton's cradle Conservation of momentum and skaters Impulse Impulse (I) is a force applied to an object for a certain amount of time. It is calculated as the product of a force (F) and the time interval (t) over which the force acts. Impulse = F ∆ t [units: N ∙ s] The “follow-through” in sports Impulse-Momentum Relationship Relationship between impulse and momentum, derived from Newton’s second law: Force in Newton, N Momentum in kg ∙ m/s Impulse in N∙ s Thus: Linear impulse = Change in linear momentum Impulse-Momentum Relationship Example: A man with a mass of 65 kg jumping from a squat position (at rest) into the air. Video analysis revealed that the velocity of his centre of mass at takeoff was 3.4 m/s. What is a) the impulse, and b) the force if it is applied over 0.2 s? a) Impulse Momentum = mass x velocity Impulse = change in momentum Therefore impulse is (65*3.4) – (65*0) = 221 N ∙ s b) Force Impulse = force * time Force = impulse / time = 221 / 0.2 = 1,105 N Work, Power and Energy Work (in mechanical context) is defined as the product of the force (F) and displacement (d) in the direction of the force. Work (W) = Force x displacement [units: Nm or Joules (J)] When the muscles of the human body produce tension resulting in the motion of a body segment, the muscles perform work on the body segment. Positive work Negative work Positive work – when the net force acting on a joint is in the same direction to the displacement. Negative work – when the net force acting on a joint is opposite in direction to the displacement. During isometric contraction, no mechanical work is done since there is no movement (although taking considerable effort). Work, Power and Energy Power is defined as the rate of doing work. Power (P) = Work / Change in time = W / ∆ t [units: Watts (W) or J (Joules)/s] or P = Fv Example: A 600 N man runs up a stairs of height of 8 m in 15 seconds. How much work is done, and how much power is generated? Solution: W = Fd = 600 x 8=4800 J P = W / t = 320 watts Work, Power and Energy Energy is defined as the capacity to do work (units is in Joules, J). Kinetic energy Potential energy Strain energy (or (energy resulting (gravitational): elastic energy; when from motion): object deforms): Strain energy Law of Conservation of Energy Energy cannot be created or destroyed; it is just transferred from one form to another. Maximum potential energy, minimum kinetic energy https://cphysics.fandom.com/wiki/Kinetic_and_potential_energy Law of Conservation of Energy Example: Pole vaulter kinetic energy stored in the vaulter’s body during running. converted into strain energy in the pole when planting the pole in the box. strain energy in the pole is converted back into kinetic energy in the vertical direction of the vaulter’s body. at the peak height, kinetic energy of the body is converted to potential energy. just before landing on the mattress, PE → KE. upon landing on the mattress, KE is converted into impact energy dissipated through the mattress, sound waves and heat etc… Summary Linear kinetics is the study of the forces associated with linear motion. Ground reaction force (GRF) – the reaction force provided by the ground upon which one is moving. Linear momentum is the product of an object’s mass and its velocity. Total momentum in a given system remains constant barring the action of external forces. Changes in momentum result from impulses – external forces acting over a time interval. Mechanical work is the product of force and the displacement through which the force acts (positive or negative). Power is defined as the rate of doing work. Law of Conservation of Energy – Energy cannot be created or destroyed; it is just transferred from one form to another. Angular Kinetics Angular Kinetics Angular kinetics is useful for the explanation of the causes of joint rotations. Newton’s laws have angular analogues that explains how torques create rotation. Newton’s Laws: Linear and Rotational Applications Torque (or Moment) The rotating effect of a force is called a torque, or moment of force. It is a vector quantity, calculated as the product of force (F) and moment arm (d). Torque= Force  moment arm (distance) [units: Nm] Muscle Moment (or Joint Moment) Example: Net torque acting at the shoulder Forces of the anterior deltoid and long head of the biceps in shoulder flexing. Torque of these muscles: (60 x 0.06 + 90 x 0.03) = +6.3 Nm. Torque of the arm: (-40 x 0.4) = –16 Nm. Net torque acting at the shoulder: +6.3 Nm –16 Nm = –9.7 Nm (assuming no other shoulder flexors or extensors active). Resulting in an extension torque where the shoulder flexors are acting eccentrically to lower the arm. Moment of Inertia Moment of inertia (I) is the inertial property of rotating bodies, which represents the resistance to angular acceleration based on both mass and the distance; the mass is distributed from the axis of rotation. Bending the joints of the upper and lower extremities brings segmental masses close to an axis of rotation which can decrease the limb’s moment of inertia. Weight ring Although both bats have the same mass, bat A is harder to swing than bat B because the weight ring on it is positioned farther from the axis of rotation. Radius of Gyration (k) The radius of gyration (k) is radial distance from the axis of rotation to a point where the body's mass could be concentrated without altering its rotational characteristics - k changes as the axis of rotation changes axis of rotation Knee angle affects the radius of gyration (k2: lower leg and k3: foot) Angular Momentum Angular momentum is defined as the quantity of angular motion that an object possesses. Angular momentum: L = I   [units: kg m2/s] where I = moment of inertia,  = angular velocity Conservation of angular momentum: The total angular momentum of a given system remains constant in the absence of external forces. Moment Arm A moment is the result of force acting at a distance from the point of motion, or the axis. In mathematical terms, a moment (M) is the product of this distance (d) and the force (F): M = d × F In translational forces, d is the length of the lever arm (or the perpendicular distance from the force vector to the centre of motion), but in rotary forces, the lever arm is the moment arm (or the perpendicular distance from the force vector to the joint’s axis of motion). Houglum, P. A., & Bertoti, D. B. (2012). Brunnstrom's Clinical Kinesiology. (6th ed.). Philadelphia: F. A. Davis Company. Torque Torque is force which is applied around an axis, producing joint motion. Torque (τ), or moment (when force is applied around an axis), is the product of a force times the perpendicular distance (d) from its line of action to the axis of motion (or its potential motion if the object is currently stationary): τ=F·d So d is the moment arm  Forces and Torques (collinear forces) Vector composition of collinear forces. (A) Two force vectors are acting on the knee: the weight of the shank-and-foot segment (S) and the exercise weight (W) applied at the ankle. These forces are added to determine the resultant force (R). The X-Y coordinate frame indicates +Y as upward; the negative sign assigned to the forces indicates a downward pull. (B) The weight of the head (H) and the traction force (T) act along the same line but in opposite directions. R is the algebraic sum of these vectors. Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4. Forces and Torques (coplanar forces) (A) Three forces are shown acting on a pelvis that is involved in single-limb standing over a right prosthetic hip joint. The forces are hip abductor muscle force (M), body weight (W), and prosthetic hip joint reaction force (J). (B) The polygon (or tip-to-tail) method is used to determine the magnitude and direction of the resultant force (R), based on the magnitude and direction of M and W. J in (A) is equal in magnitude and opposite in direction to R in (B). Determine the resultant force by polygon method Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4. Forces and Torques (coplanar forces) Determine the resultant force by parallelogram method Parallelogram method is used to illustrate the effect of two force vectors ( F 1 and F 2 ) produced by contraction of the flexor digitorum superficialis and profundus muscles across the metacarpophalangeal (MCP) joint. The resultant force (R) vector creates a bowstringing force resisted by the flexor pulley and collateral ligaments (force P in blue) at the MCP joint. Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4. Composing force vectors Collinear force vectors can be combined by simple addition or subtraction. Nonparallel, coplanar force vectors can be composed by using the polygon (tip-to-tail) method or the parallelogram method. Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4.  Resolution of Forces The muscle force (M) produced by the brachioradialis is represented as the hypotenuse (diagonal) of the rectangle. The X component (M X ) and the Y component (M Y ) are also indicated. The internal moment arm (IMA) is the perpendicular distance between the axis of rotation (red circle) and M Y. The X-Y coordinate reference frame is placed so the X axis is parallel with the body segment of interest; the thin black arrowheads point toward positive directions. Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4. Internal vs External Forces acting on the body Resolution of internal forces (red) and external forces (black and green) for an individual performing an isometric knee extension exercise. (A) The following resultant force vectors are depicted: muscle force (M) of the knee extensors; shank-and-foot segment weight (S); and exercise weight (W) applied at the ankle. (B) The free body diagram shows the forces resolved into their X and Y components. The joint reaction force (J) is also shown (blue). In both panels A and B, the open circles mark the medial-lateral axis of rotation at the knee. (Vectors are not drawn to scale.) Observe that the X-Y coordinate reference frame is set so the X direction is parallel to the shank segment; thin black arrowheads point toward the positive direction. Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4. Effect of change of joint angle on torque Changing the angle of the elbow joint alters the angle-of-insertion of the muscle to the forearm. These changes, in turn, alter the magnitude of the X (M X ) and Y (M Y ) components of the biceps muscle force (M). Using trigonometric functions, the magnitudes of M X and M Y can be found for each position: (A) angle-of- insertion of 20 degrees; (B) angle-of-insertion of 90 degrees; (C) angle-of-insertion of 45 degrees; and (D) angle-of-insertion of 15 degrees. Although the magnitude of M is assumed to be constant (120 N), the changing magnitude of M Y alters the internal torque significantly throughout the range of motion. The internal moment arm (IMA) is drawn as a brown line extending from the axis of rotation (black dot) to the point of application of M and remains constant throughout panels A to D. Note that the X-Y coordinate reference frame is set so the X direction is always parallel to the forearm segment; thin black arrowheads point toward the positive direction. Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4. Changing the angle of elbow flexion can alter both internal and external torque potential. (A) The 90-degree position of the elbow maximizes the potential for both the internal and the external torque. (B) With the forearm horizontal and the elbow closer to extension, the external torque remains maximal but the overall biceps force (M) must increase substantially to yield sufficient M Y force to support the weight. EMA, external moment arm; IMA, internal moment arm; M, muscle force; M Y , Y component of the muscle force; W, exercise weight. Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4. Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4. Neumann, D. A., (2017). Kinesiology of the musculoskeletal system : foundations for rehabilitation (Third edition.). Elsevier, chapter 4. Which position produces the greatest torque at the shoulder? Houglum, P. A., & Bertoti, D. B. (2012). Brunnstrom's Clinical Kinesiology. (6th ed.). Philadelphia: F. A. Davis Company. Using proper body mechanics includes moving objects close to the body. In (A), the object has a long lever arm and will place a much greater force on the body than the object in (B) when it is brought closer to the body so its lever arm is shortened. Houglum, P. A., & Bertoti, D. B. (2012). Brunnstrom's Clinical Kinesiology. (6th ed.). Philadelphia: F. A. Davis Company. Resolution of forces Figure 2.16 Two forces acting in different directions from the same point create a resultant vector. The resultant vector is made up of a rotation force and a force that either compresses or distracts the joint. A) Shows a large compression force vector and small rotational force vector. B) Shows rotational and distraction forces that are close to equal to each other but create a larger resultant force than either of them. C) Since the applied force vector is perpendicular to the lever, there is no distraction or compression force, so all of the muscle’s force rotates the segment Houglum, P. A., & Bertoti, D. B. (2012). Brunnstrom's Clinical Kinesiology. (6th ed.). Philadelphia: F. A. Davis Company. By resolving the forces generated by clavicular and sternal portions of the pectoralis major muscle (CPM and SPM respectively), what shoulder motion results? Houglum, P. A., & Bertoti, D. B. (2012). Brunnstrom's Clinical Kinesiology. (6th ed.). Philadelphia: F. A. Davis Company. Based on these two drawings of the deltoid, in which anatomical position would a constant muscle contraction produce more force to elevate the arm? Why? Houglum, P. A., & Bertoti, D. B. (2012). Brunnstrom's Clinical Kinesiology. (6th ed.). Philadelphia: F. A. Davis Company. Centre of gravity and centre of mass Centre of gravity (CG) of an object or body is the theoretical point around which the mass of the object is balanced and around which that gravity acts. Also called the centre of mass (COM) – COM is the point of origin for gravity’s vector force. The CG of the adult body in the anatomic position is slightly anterior to the second sacral vertebra (55% of a person’s height). It is usually near the level of ASIS. Usually higher in male than female. Why? Change of body position changes CG. Consider sit-ups, why is it easier to perform with arms stretched out than hands behind the head? Houglum, P. A., & Bertoti, D. B. (2012). Brunnstrom's Clinical Kinesiology. (6th ed.). Philadelphia: F. A. Davis Company.  Where is the CG in each of the pictures? Base of support and balance A body is stable when the line of gravity runs through the center of its base of support. A body’s base of support (BOS) is the area within the points of contact of the body and any object the individual relies on for support. Houglum, P. A., & Bertoti, D. B. (2012). Brunnstrom's Clinical Kinesiology. (6th ed.). Philadelphia: F. A. Davis Company.