Biomechanics Lecture Notes PDF

 General exam rules Be on time Phones off and put away; Notes closed and put away No hats You are allowed a non-programmable calculator Consult SFU Website to learn about your responsibilities as a student to ensure Academic Integrity is upheld. – http://www.sfu.ca/st...

 General exam rules Be on time Phones off and put away; Notes closed and put away No hats You are allowed a non-programmable calculator Consult SFU Website to learn about your responsibilities as a student to ensure Academic Integrity is upheld. – http://www.sfu.ca/students/academicintegrity.html If you are sick or have a personal emergency you need to fill out and submit a Self Declaration Form within 48 hours. – under Syllabus find BPK missed exam policy on Canvas You will not be allowed to go to the restroom. Hand in exams to your own TA at the end with photo ID.  Biomechanics Course Learning Outcome 8. Apply basic biomechanical principles (Newton’s laws of motion, mass, weight, force, work, torque and power) to human movement. (I) (LE, IC) Learning Goal Develop a working knowledge of biomechanical principles and terminology and apply this understanding to human movement. https://elite-performance-therapy.com/ https://www.linkedin.com  Biomechanics Learning Outcomes - Define biomechanical terminology. - Define lever and its components force point, resistance point and fulcrum. - For each of the three classes of levers define, provide examples and draw the relative positioning of the force arm, resistance arm and fulcrum. - Define mechanical advantage of levers and draw speed and mechanical levers. - Define moment arm and torque including formula. - Define center of gravity, describe why it is useful to determine and describe how it can change with body positioning. - Describe balance and stability and what can influence them. - Describe through definition and example each of Newtons three laws of motion. - Define momentum and be able to calculate the outcome of a collision between two objects. - Define work and power, including their units and formulas. - Describe the components of the human gait cycle and describe the differences between walking and running. Biomechanics I. Application of Biomechanical Analyses II. Biomechanical Terminology III. Levers of the Human Body IV. Center of Gravity V. Newton’s Laws of Motion VI. Work and Power Relationships VII. Walking Versus Running Biomechanics Biomechanics - the application of mechanical laws to living structures, specifically to the locomotor system of the human body. fusionsport.com I. Application of Biomechanical Analyses Improvement of sports skill techniques Design of sports equipment Prevention of injuries Clinical analysis of movement pathologies Design of prostheses Design of rehabilitation devices Animation for film and video games Ergonomic redesign in the workplace Biomechanics I. Application of Biomechanical Analyses II. Biomechanical Terminology III. Levers of the Human Body IV. Center of Gravity V. Newton’s Laws of Motion VI. Work and Power Relationships VII. Walking Versus Running II. Biomechanical Terminology Qualitative movement analysis - a non-numerical description of a movement based on direct observation. – Conducted primarily by teachers and coaches. Quantitative movement analysis - a movement is analyzed numerically based on measurements from data collected during the performance of the movement. – Conducted by researchers.  II. Biomechanical Terminology Terminology and diagrams - Refer to Unit 13 in Lab Manual. Mass – the quantity of matter contained in an object. – Units = kilograms (kg) Force – mass X acceleration. Units = Newtons (N) – 1 N = (1 kg) (1 m/s 2) Weight – the amount of gravitational force exerted on a body – Weight = mass X acceleration of gravity = ma g – Acceleration of gravity = 9.81 m/s2 – Units of weight – Newtons – If a person has a mass of 80 kg, his weight = (80 kg) (9.81 m/s 2) = 785 N  II. Biomechanical Terminology Volume – the amount of space that a body occupies Pressure – force distributed over a given area – Pressure = F/A (Units = N/m2 or N/cm2) Compression – pressing or squeezing force directly axially through a body Tension – pulling or stretching force directly axially through a body II. Biomechanical Terminology Shear – force directed parallel to a surface Mechanical stress = F/A Similar to pressure Biomechanics I. Application of Biomechanical Analyses II. Biomechanical Terminology III. Levers of the Human Body IV. Center of Gravity V. Newton’s Laws of Motion VI. Work and Power Relationships VII. Walking Versus Running III. Levers of the Human Body Terminology and diagrams - Refer to Unit 13 in Lab Manual. Lever Force point Resistance point Fulcrum Force arm Resistance arm First-Class, Second-Class, Third-Class levers Mechanical advantage Force lever Speed lever III. Levers of the Human Body A lever is defined as a rigid bar that turns about an axis. In the body, the bones represent the bars and the joints are the axes. Contraction of the muscles provides the force to move the levers.  III. Levers of the Human Body The three parts of a lever are: – The force point (F) — The exact point where the effort is applied. (muscle insertion) – The resistance point (R) — The exact point on which the resistance acts. (segment plus external weight) – The fulcrum (A) — The axis of motion.  III. Levers of the Human Body The force arm (FA) of a lever is the perpendicular distance from the fulcrum to the line of action of the force acting on the force point. The resistance arm (RA) of a lever is the perpendicular distance from the fulcrum to the line of action of the resistance acting on the resistance point.  III. Levers of the Human Body The relative arrangement of the force point, 1 resistance point and fulcrum distinguishes the three classes of 2 levers. – R point - first, second, third 3 respectively  III. Levers of the Human Body FIRST-CLASS LEVERS – A first-class lever has its fulcrum at some location between the force point and the resistance point – A typical example of a first-class lever is a teeter-totter or seesaw.  III. Levers of the Human Body SECOND-CLASS LEVERS – Second-class levers have their resistance point at some location between the force point and the fulcrum. – The wheel barrow is a good example: – the wheel is fulcrum – the weight sitting in the box is the resistance point – and the handle is the force point. III. Levers of the Human Body THIRD-CLASS LEVERS – A third-class lever has its force point at some location between the resistance point and the fulcrum. – This class of lever is the most common in the body, – it permits the muscle to be inserted near the joint and to produce distance and speed of movement – although at a sacrifice of force.  III. Levers of the Human Body THE MECHANICAL ADVANTAGE OF LEVERS Mechanical advantage of a lever – the ratio of force arm length to resistance arm length The efficiency with which a lever is able to magnify forces is described by its mechanical advantage (MA) or mechanical ratio. Mechanical Advantage = Force Arm Resistance Arm  III. Levers of the Human Body Whenever the force arm (FA) of a lever is longer than its resistance arm (RA), the mechanical advantage favours application of force at the sacrifice of speed, and the lever is called a force lever. 50 Newtons Example: – MA = FA/RA – If, FA = 4 m, RA = 2 m – MA = 4m/2m = 2 Only 50 N of force is needed to lift 100 N object.  III. Levers of the Human Body Conversely, when the resistance arm is longer than the force arm, the lever favours speed and range of motion at the sacrifice of force, and is called a speed lever. Example: – MA = FA/RA – If, FA = 1 m, RA = 3 m – MA = 1m/3m = 1/3 Need to apply 300 N to lift 100 N object. But when the force point is going down by 1 m, The resistance point will move 3 m in the same period III. Levers of the Human Body Mechanical Advantage = Force Arm Resistance Arm 1ST Class lever – Can have MA = 1, > 1 or < 1 – MA = 1 (FA=RA) – MA > 1 (FA>RA) – MA < 1 (FA 1 – Always force lever 3rd Class lever – MA < 1 – Always speed lever  III. Levers of the Human Body Moment arm – the perpendicular distance between the force’s line of action and the axis of rotation. Moment arm A Moment arm B Torque – the product of force and the perpendicular distance (moment arm) from the force’s line of action to the axis of rotation. It may be thought of as rotary force. – Torque = Force (N) x moment arm (m) – Units of Torque = Newton-meters (N∙m) Biomechanics I. Application of Biomechanical Analyses II. Biomechanical Terminology III. Levers of the Human Body IV. Center of Gravity V. Newton’s Laws of Motion VI. Work and Power Relationships VII. Walking Versus Running  IV. Center of Gravity The center of gravity (CG) in human body is an imaginary point in the center of the body where the weight of the body is balanced. It may also be defined as: The point of intersection of the three cardinal planes of the body—frontal, transverse, and sagittal. The point of exact centre, around which the body may rotate, freely in all directions. The point around which the weight is equal on all opposite sides. A and P Open Stax IV. Center of Gravity For the human body in anatomical position, the CG is approximately 5 cm anterior to the second sacral vertebra, or 6 cm below the belly button. On average, it is slightly higher in males than in females – 57% versus 55% of height. The exact location of the center of gravity varies from person to person depending on body proportions. IV. Center of Gravity The CG is influenced by changing body position or limb positions. The addition of external weight, such as a backpack, will relocate the CG. Segmentally each body area contains its own center of gravity. Derek Drouin - Olympic Gold medalist 2016 (2.38m), Bronze 2012 Photo Credit: @iaaforg  IV. Center of Gravity A. Why Is It Useful to Determine CG? 1. Used to describe the movement of the body through space 2. Important for stability 3. It is an important factor in calculating the of amount of work done. Dimitri Otis/Getty Images photo: Mike Ridewood IV. Center of Gravity B. Location of Center of Gravity 1. Reaction board method - used for a static position of the human body. – Assume that the center of gravity is the fulcrum or balance point and then apply the Principle of Levers. – R1 – scale reading reaction board – R2 – scale reading reaction board plus subject L-Y Y F2 F1 F x FA = R x RA F2 = R2-R1 F1 × Y = F2 × (L – Y) Y = F2L/M IV. Center of Gravity B. Location of Center of Gravity 1. Reaction board method CG in CG in CG in Sagittal Line Frontal Line Transverse Line C. Balance and Stability Balance is defined as the ability to control equilibrium. Stability - firmness of balance For balance to be maintained in any stationary position, the CG must remain over the base of support. Whenever the CG passes outside the base of support, the body is off balance in that direction. If a heavy object is carried close to the body's CG, there will be less likelihood of a loss of balance. Well balanced Unbalanced Borderline balance Balanced CoG is within is CoG outside CoG is on the CoG is within the Base of Support the BoS border of BoS the BoS  C. Balance and Stability Stability can be increased by: – Increasing body mass – Increasing the size of the base of support in the direction of the line of action of an external force – Increasing friction between the body and the surface contacted – Horizontally positioning the CG near the edge of the base of support towards the oncoming external force – Vertically positioning the CG as low as possible Biomechanics I. Application of Biomechanical Analyses II. Biomechanical Terminology III. Levers of the Human Body IV. Center of Gravity V. Newton’s Laws of Motion VI. Work and Power Relationships VII. Walking Versus Running  Sir Isaac Newton 1642-1727 Formulated the Laws of Gravity, Laws of Motion, and Laws of Optics Devised calculus Founder of modern science Considered to be the most important scientist of the second millennium AD V. Newton’s Laws of Motion First Law - Law of Inertia “A body will maintain in a state of rest or constant velocity unless acted on by an external force that changes the state.” The amount of inertia a body possesses is directly proportional to its mass. V. Newton’s Laws of Motion Second Law - Law of Acceleration Force = mass X acceleration – force in N (newton) – mass in kg – acceleration in m/s2 Force = mass X acceleration V. Newton’s Laws of Motion How much force must be applied by a golf club to give a stationary 0.10 kg ball an acceleration of 40.0 m/s2? Given: – Mass = 0.10 Kg – Acceleration = 40.0 m/s2 – Looking for force. Formula: – F = ma F = (0.10kg)(40.0m/s2) = 4.0 N It requires 4.0 N of force to give a stationary 0.10 kg ball an acceleration of 40.0 m/s2. V. Newton’s Laws of Motion Third Law - Law of Reaction “When one body exerts a force on a second body, the second body exerts a reaction force that is equal in magnitude and opposite in direction on the first body.” Momentum Quantity of motion that an object possesses Linear Momentum = mass X velocity A mechanical quantity that is important in situations involving collisions. tsn.ca Momentum After the collision occurs, in which direction are they going to travel? Momentum Momentum = mass X velocity Pa= 90kg x 6m/s Pb= 80kg x 7m/s Pa = 540 kgm/s Pb = 560 kgm/s After the collision occurs, in which direction are they going to travel? Momentum Ma < Mb (540 kg∙m/s < 560 kg ∙ m/s) As Player B has more momentum than Player A, Player B will push player A backwards when they collide. What essential qualities does a great running back have in terms of momentum? Biomechanics I. Application of Biomechanical Analyses II. Biomechanical Terminology III. Levers of the Human Body IV. Center of Gravity V. Newton’s Laws of Motion VI. Work and Power Relationships VII. Walking Versus Running VI. Work and Power Relationships Work = force X distance – Units of work - 1.0 Nm = 1.0 J (joule) Power = work per unit of time = (force x distance) t = force X velocity - Units of power = watts - 1.0 W = 1.0 J/sec. VI. Work and Power Relationships A force of 20 N pushing an object 5 m in the direction of the force. How much work is done? – Given: F = 20 N, d = 5m – Work = F x d = 20N x 5m = 100Nm or 100 J If you do 100 joules of work in two seconds, how much power is used? – Given: Work = 100 J, time = 2 s – Power = work/time = 100J/2s = 50 W (50 J/s) Biomechanics I. Application of Biomechanical Analyses II. Biomechanical Terminology III. Levers of the Human Body IV. Center of Gravity V. Newton’s Laws of Motion VI. Work and Power Relationships VII. Walking Versus Running Human Walking Gait Cycle princetonmedicine.com VII. Walking Versus Running 1. In running there is a period when both feet are off the ground – double float phase. Running is a series of jumps. 2. In running, there is no period when both feet are in contact with the ground at the same time 3. In running, the stance phase is a much smaller portion of the total gait cycle than in walking. Human Running Gait Cycle atlantasportrecovery.com Fellrnr.com Powerwalk – Kinetic Energy Harvester Max Donelan – BPK Professor bionicpower.com Powerwalk – Kinetic Energy Harvester 20% drop in metabolic cost and a 28% drop in muscle activity with Harvester on  VII. Walking Versus Running Running speed = stride length X stride rate Length of stride is dependent primarily upon leg length and the power of the stride. Leg speed (frequency) is mostly dependent on speed of muscle contraction and neuromuscular coordination (skill) in running. VII. Walking Versus Running 100 m sprinter comparisons Berlin World Championship 2009 Usain Bolt Rest of Finalists Time (s) 9.58 * 9.91 Velocity (m/s) 10.44 10.09 Step frequency (Hz) 4.472 4.53 Number of Steps 41 44.91 Step Length (m) 2.449 2.23 * World record Stuhec Bioengineering (Basel) 2023 Nov VII. Walking Versus Running Running mechanics vary from person to person and they vary in the same person running at different speeds. At slow running speeds, complete foot contact is used. runners tend to run more erectly, As running speed increases, the amount of foot contact becomes less. the typical sprinter leans forward at about 15 degrees from the perpendicular.  VII. Walking Versus Running Usain Bolt 100m World Record 9.58s Berlin World Championship 2009 Stuhec Bioengineering (Basel) 2023 Nov BPK Honours Thesis 2019 – Wakeling Lab Methods Muscle activity was recorded using an electromyograph (EMG) for nine muscles Accelerometer and foot switch data was also collected Participants walked at a self-selected cadence in seven conditions Image courtesy of C Sison  Flat Down Stairs Raw EMG Image courtesy of C Sison