physical interaction enhance performance minimizing the risk

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1 Kin 420 Midterm 1 review What are Tichauer s 15 principles o Keep elbows in o Minimize spine moments o Avoid covert lifting tasks o Gender differences o Optimize joint position for max muscle force o Reduce forward reach o Avoid antagonistic fatigue o Avoid muscular insufficiency o Avoid straight line wrist movements o Gloves o Compression ischemia o Avoid high forces on hands o Avoid wrist deviation o Chair design o Vibration Define occupational biomechanics o The study of the physical interaction of workers with tools, machines, and materials o so as to enhance the worker s performance while minimizing the risk of musculoskeletal disorders. Why is ergonomics important o Cost of being wrong in work design is high o injuries, lost productivity, poor quality o Promotes good employee relations o Competition is doing it o Scientific knowledge exists and is advancing to provide valid means to improve work o Good public relations o Moral concern to do no harm o Legal requirements mandate somewhat Define anthropometry: o The science that examines the size, mass, shape of the human body What are the questions anthropometry can answer o Who can fit, who can reach, who can see What is the difference between link and reference measurements o Reference measurements are measureable distances between boney landmarks, link measurements are taken from joint centre and require analysis What is the problem with anthropometric data o Its derived from specific populations, using specific techniques under specific conditions o No such thing as the average person List the pros and cons for the proportional link scaling method from drillis and contini o Pros: simple and consistent

2 o Cons: individuals wont fit this data sometimes, not population sensitive How would you calculate what percentile of the female population has a ht of 166 cm o Find the z score o Z= (actual score mean value) / standard deviation What are the problems to classic functional anthro design o Time consuming and costly o Not very creative and cant be adapted to all situations o Increases design bias What are the advantages to computer based biomechanical models o 3D, scalable o Lower design time and cost What are the general limitations of anthropometric design o Assume consistency of link length and proportions o Link data assumes additivity o Articulations are simplified o Rigid torso o R.O.M limits fixed How do you solve 2D anthropometry problem o Solve elbow/shoulder location (normally fixed angle, use trig) o Find length between elbow and part L= (X 1 X 2 ) 2 + (Y 1 Y 2 ) 2 What are some problems with 2D biomech assessment o Many assumptions i.e. solve reach not functional grip, limited flexion, foot placement Give the formula for the risk of tissue damage o Load > tissue tolerance Define deformation o Change in shape of material due to an applied load Give the formula for stress o = Force / Area Give the formula for strain o Є= L / L 0 Draw and label the stress strain curve Explain the stages of the stress strain curve o P stress and strain are linearly proportional o E elastic limit (after deform cant be fully recovered)

3 o Y yield point, considerable deform with minimal increases in stress o U ultimate strength, most stress tolerable o R rupture point, 2 samples What is Youngs Modulus and where is it calculated o It is the stiffness and its formula is E= stress/strain o Only calculated in elastic region Define visoeoelasticity o material properties are time and load dependant how does fast loading affect stress/strain differently than slow loading o strain increases rapidly with stress then levels off what does the creep curve look like o stress stays constant but strain increases over time what is hysteresis o energy loss during un/loading Draw the stress strain curves for cancellous and cortical bone and explain how this applies to injury o Since cortical bone has a a short plastic region and is stiff, it ruptures under little strain, the cancellous bone has a retardedly long plastic region and individual trabeculae may break but as a whole remains solid. How does the direction of loading change the stress strain curves o As loading deviates from compression axis the curves the curves shorten in both stress and strain and the slope decreases How does compression and tension vary with exercise intensity

4 How does the stress strain curve vary from ligaments to tendons o Ligaments have wavy fibers and it takes longer the develop stress Define toe region o Strain increases but no stress List and describe the 3 types of cartilage o Articular highly orgainised collagen matrix, occurs at joints o Fibrocartilage islands of articular cartilage packed together, like vertebral discs o Elastic cartilage more elastin than collagen, ears/nose Draw the 3 zones of cartilage o Superficial (horizontal), middle ( criss cross), deep (longitudinal) Explain the 2 articular cartilage theories o Boundary theory states that the absorbed molecules prevents surface-to-surface contact o Fluid film theory states parallel surfaces slide past each other on lubricated fluid, if surfaces aren t parallel the fluid creates a wedge keeping the surfaces apart Draw and label the deformation vs. time curve for articular cartilage What is the loading rate that is the highest risk of injury for the IVB o 10,000 N/s What is the loading rate that is highest risk of injury for the endplate o Under 3000 N/s Which tissue is more at risk with a loading rate of 16,000N o Its dependant on the situation

5 Give an example of an acute and cumulative injury o Endplate fracture and disk herniation What is the one take home message about length tension relationship o ROM window doesn t have to be symmetrical Describe the velocity tension relationship o Increasing the speed of shortening decreases tension because of inefficient cross-bridging and viscous intramuscular friction Explain the 2 types of fatigue o Central fatigue processor fatigue, decrease in voluntary strength. o Peripheral fatigue local fatigue, changes in muscle activation and AP. What are the 2 causes of fatigue, which type happens most often in work o HFF sustained forceful muscle contraction, high recovery o LFF sustained low level contraction, slow recovery (most common work prob) What is the definition of a moment o The tendency of a force applied to an object to cause the object to rotate, twist or bend about and axis or joint Size of the tendency can be found by multiplying the length of the perpendicular distance from the axis to the line of action of the force by the size of the force. Which side will have the bigger moment both have the same What are the 3 things we need to solve reaction forces and moment o Anthropometric data o Hand/force data o Posture What are the steps for solving an external link problem o State assumptions o Define reference system o Force equilibrium=0 therefore find reaction forces o Moment equilibrium =0 therefore find moment at joint What is the difference between a resultant and a reactant force o They are opposites of each other What is the order to approach solving a internal force problem o Define reference system o Find external moment o Solve muscle force o Find overall force equilibrium What will the biggest force contributor normally be in an equilibrium situation o Internal muscle forces What are the 3 steps to solve a 3D problem o Determine magnitude and direction of force vector o Find moment are vector from force o Perform cross product to get moment What do you need to solve a dynamic situation o Trajectory of hand o Velocity and acceleration

6 o Weight ect? What is the limitation to static calculations o Always under estimate moment (MOMENT PEEKS) What is the most common back ailment people see the doctor for o Non specific back ache o More than 50% of complaints Why bother modeling the low back o Big problem o Complex joints o Cant measure on humans due to risk How big of a problem is low back pain o 15 billion a year spent o 600, 000 cases a year o 20 % of all comp cases o 25% of all comp costs o 70% of population is affected What are the 3 most prevalent causes of injury o Lift, twist, bend How do you find β o Read chart with knee angle How do you find α o 40 + β explain the 3 models to analyze the low back o optimization estimation of muscle forces and lines of action o EMG measures muscle activity o Neural networks estimates muscle forces from measured situations What are the causes off carpal tunnel syndrome o Repetitions, force, vibration, temp What is the prevalence of CTD s o 2-10% of workers a year affected o Up to 80% of disability Describe carpal tunnel o When meadian nerve goes through flexor retinaculum, during flexion nerve is compressed How much greater is the force in the tendon than the force being produced o 3 What components contribute to tension in flexor tendon o Hand size o Applied load What is F N dependant on o Normal wrist F T and R o Injured wrist α and µ What are 3 things to remember about F N o anthro and gender don t have a big impact o posture is a key factor o flexion increases F N more than extension what force causes residual strain in the muscle o < 80N Explain the 3 equations at the wrist o F N = F T / R o F s = F n / µ o F R = 2F T sin (angle/2)

7 Extension radius is less than flexor Prove that biomechanics is consistent with epidemiology o Load moments o Repetition o Maintain neutral posture o Wrist size isn t really important o Flexion worse than extension Why is muscle wrapping important o In optimization models its important to account for boney structures that impede the path of the muscle changing the moment arm and therefore required force production Why bother modeling the shoulder o Gain insight into a closed system o Test untestable hypothesis and quickly o Don t need subjects What are the 4 types of shoulder models which one s the best o External strength/global demand of system o Geometric kinematic of MSK system o Internal forces of muscle, lig, tendon o Composite combo off all of the above (BEST) Describe the characteristics of the external model o Top down 3 link o Includes inertia o Output is strength and capacity, shows where person is WRT population What is a problem with using motion data with the shoulder, what is the solution o Cant track the scapula because it uses markers, use geometric modeling because it tracks joint center What is the point of using internal models (muscle forces) o Find injury potential, fatigue o Tissue loading What is the problem with optimization muscle force models o Assume body is minimizing muscular loading by only activating one muscle with the biggest moment arm o Doesn t account for co-contraction