Class Notes (835,244)
Canada (509,045)
BPK 142 (161)
Paul Lee (8)
Lecture

Biomechanics --Fill in the blanks style lecture notes with occasional extras about what was especailly important to remember and some further explanations.

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Department
Biomedical Physio & Kines
Course
BPK 142
Professor
Paul Lee
Semester
Summer

Description
1 BIOMECHANICS Biomechanics - the application of mechanical laws to __living___ structures, specifically to the ___locomotor____ system of the human body. I. Uses 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 Qualitative analysis - a __non-numerical_____ description of a movement based on direct ___observation____. Conducted primarily by teachers and coaches. Quantitative analysis - a movement is analyzed __numerically__ based on ___measurements_____ from data collected during the performance of the movement. Conducted by researchers. II. Levers of the Human Body Refer to Unit 13 in Lab Manual. Lever –a rigid bar that turns about an axis – in the body, the bones represent the bars and the joints are the axes. Force point – the exact point where the effort is applied Resistance point –the exact point on which the resistance acts Fulcrum – the axis of motion 2 Force arm – the perpendicular distance from the fulcrum to the line of action of the force acting on the force point Resistance arm – the perpendicular distance from the fulcrum to the line of action of the resistance acting on the resistance point First-class – its fulcrum at some location between the force point and the resistance point [ex. Is a teeter-totter] Second-class – have their resistance point at some location between the force point and the fulcrum [ex. Wheel barrow, swinging door] Third-class levers – has its force point at some location between the resistance point and the fulcrum [Most common in the body since it permits the muscle to be inserted near the joint and to produce distance and speed of movement although at a sacrifice of force. Ex. Shoveling, swinging a golf club] Mechanical advantage - Force level Speed lever 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 gr2vity___ = ma g Acceleration of gravity = 9.81 m/s Units of weight – _Newtons (N)____ If a person has a mass of 80 kg, his weight = (80 kg) (9.81 m/s ) = 785 N Torque – the product of force and the perpendicular __distance__ from the force’s line of action to the axis of rotation. It may be thought of as rotary force. 3 Torque = Force (N) x Moment arm (m) Units = Newton-meters (N∙m) Moment arm – the perpendicular distance between the force’s line of action and the axis of __rotation____. The Principle of Levers -This principle states that a lever of any class will balance when the produce of the force times the distance from the point of application of the force to the fulcrum is equal to the resistance times the distance from the point of application of the resistance to the fulcrum or axis. Force x force arm = Resistance x Resistance Arm F x FA = R x RA Example: Given Elbow flexed at 90 degrees 10-kg mass held in the hand Assume that: Angle of muscle pull is 90 degrees [not true] Then: FA = 5cm [i.e biceps muscle inserts 5cm from the joint axis] RA =35cm Question: How much force does the biceps muscle have to exert to hold the weight? Solution: [TIP – Remember to convert the units of measure!!!!] F x FA = R x RA [You can use 10 instead of 9.81] F x 5cm = (10kg x 9.81) x 0.35m F = 70 x 9.81N F = 687 N Levers of the human body Conversely, when the resistance arm is longer than the force arm, the lever gfavours speed and range of motion at the sacrifice of force nad is called a speed lever  this is the most common lever in the human body 4 Mechanical advantage = force arm/resistance arm -Is the mechanical advantage of a first class lever greater than, less than or equal to one? IT COULD BE ANY!! – This is because of the axis or rotation. RA and FA could be exactly the same or it could be closer to either the FA or RA. -For a second class lever  The 2 class lever is always MA > 1 because it’s always a force lever rd 3 class MA<1 and is ALWAYS a speed lever because the mechanical advantage is always less than one. Mechanical advantage of a lever – the ratio of force arm length to __reisistance arm___ _________ length Volume – the amount of __space__ that a body occupies Pressure – force distributed over a given __area__. Units = N/cm 2 Pressure = F/A Compression – pressing or squeezing force directly _axially__ through a body Tension – pulling or stretching __force__ directly axially through a body Shear – force directed parallel to a _surface_ Mechanical stress = F/A Similar to __pressure____. Is it better to be stepped on by a woman wearing a spike heel or a woman 5 wearing a smooth-soled athletic shoe? Given: -Woman’s mass = 50kg -the spike heel area (As) =5cm^2 -the athletic shoe area (Aa)=100cm^2 Solution: Formulas -Weight (fg) =mag (assume ag=10m/s^2) -Pressure (P) =Force/Area Woman weight = 50kg x 10m/s^2 = 500N The spile heel pressure = Fg/As = 500N/5CM^2 = 100N/cm^2 The athletic shoe pressure = Fg/Aa = 500M/100cm^2 = 5N/cm^2 Comparison = 20 times more pressure with high heel Lifting A Heavy Object From the Floor 1. If the object is very heavy, get someone to _help__ you. Don't be a "hero". Use techniques that __minimize___ the actual weight of the load being handled. 2. Stand facing the object with your feet _flat_ on the floor, at shoulder _width__, and pointing straight _ahead_. Ensure that you have a stable base of support so that you don’t __slip__ as you are lifting the load. 3. Face the object in the __direction__ which you intend to move with it, so that you don't have to turn while holding the object. Avoid twisting and the simultaneous generation of high twisting torques. 4. Keep the object as _close__ to your body as is convenient to minimize the reaction torque on the low back. When 40cm away, Tobject = 0.4m X 100N = 40NM [Newton meters] When 20cm away, Tobject = 0.2 X 100N =10NM 5. Get a good _grip_ on the object so that you don’t lose control of it as you are lifting it. 6 6. Bend at the __knees__ and __hips__, and keep your back as __straight_ as possible. Avoid a fully flexed or bent spine. 7. Lift the object using the knee and hip extensor muscles, not by pulling upwards with the __arms__ and ___back___. 8. Carry the object close to your __center___ of gravity. The flat back lifting posture has been found to be better overall than a ___rounded__ back in minimizing _L5/S1___ disc
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