PSU IE 553 - Mechanical Work Capacity Evaluation

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Slide 1Slide 2Mechanical Work Capacity Evaluation (Ch. 4)Slide 4Defining Joint MotionGoniometers - 1Goniometers -2Range of MotionMuscle StrengthStatic (Isometric) StrengthStatic Strength Testing Guidelines (Caldwell regimen - AIHA (1974))Effect of Posture on StrengthBasis for ROM VariationExtensive Population Data (UM PEST, 1978)Dynamic vs. Static StrengthDynamic (Isokinetic) StrengthPsychophysical StrengthSlide 18Comparison of Strength TestsPersonal Factors Affecting StrengthIE 5531IE 553 Engineering of Human WorkDr. Andris FreivaldsClass #6IE 5532IE 553 Engineering of Human WorkDr. Andris FreivaldsClass #6IE 5533Mechanical Work Capacity Evaluation (Ch. 4)For any measurement, concerned for:•Standardization: follow same procedures•Accuracy (validity): closeness to “truth”•Repeatability: closeness of grouping–Test-retest r–Coefficient of variation (CV) = σ/μ•Ease of use (industry vs. lab)•Flexibility, interference on job•Cost (industry vs. lab)IE 5534Standard Anatomical PositionPlanes:1) Sagittal2) Frontal3) TransverseDefining Joint Motion1) For job requirements2) Input to biomech modelsIE 5535Defining Joint MotionIE 5536Goniometers - 1•Goniometer (protractor)•Elgon (potentiometer)•Flexometer (gravity sensing)•Spatial imaging–Photogrammetry (cameras)–Computer collected (Vicon)http://www.vicon.com/IE 5537Goniometers -2http://www.nexgenergo.com/ergonomics/biosensors.htmlPenny&Giles/Biometrics Lumbar Motion Monitorhttp://www.nexgenergo.com/ergonomics/lumbarmm.htmlIE 5538Range of Motion•Age: 0-10 base, 10-16 10%↓, >16 constant•Gender: Fem > Males (by 10%)•Obesity: ↓ ROM, ↑ bulk, ↓ activity•Exercise: ↑ flexibility•Two-joint muscle effect:–Due to length-tension relationship–47%↓ shoulder flex with elbow flex–Passive vs volitional ROMIE 5539Muscle Strength•Need for strength evaluation:–Safe, healthy working conditions–Inputs to biomechanical models•MVC (max voluntary contraction):–Must be < bone/tissue yield strength–Typically ~ 30%–Must > job strength requirements (JSR)–Otherwise injuryIE 55310Static (Isometric) StrengthLoad cellIE 55311Static Strength Testing Guidelines(Caldwell regimen - AIHA (1974))•Instructions: “Increase slowly and hold”•Duration of 4-6 seconds•Record peak and 3-sec average•Adequate rest, ≥ 2 min between trials•3 repetitions (need μ, σ)•Avoid coercion, environmental distractions•Standardize test procedures•Record subject attributes•Safe (<1/1,000), reliable (r > 0.89), quick (10min)IE 55312Effect of Posture on StrengthIE 55313Basis for ROM VariationIE 55314Extensive Population Data(UM PEST, 1978)IE 55315Dynamic vs. Static Strength•Static underpredicts max lifting capability by 50%–Due to angled pull•Static overpredicts max lifting capability by 10-20%–Due to inertial effects•Dynamic better?•R = 0.9 with max lift (Kamon,1981)•But much more variable•Plus force-velocity effect•Need isokinetic controlIE 55316Dynamic (Isokinetic) Strength Cybex KinComMiniGymIE 55317Psychophysical Strength•Developed by Snook (1978), Liberty Mutual•Maximum acceptable weight (MAW) through psychophysical estimation•Tables of MAW as population %:–Gender (M, F)–Tasks•Lift/lower: Knuckle/shoulder/arm height, box size•Push/pull: initial/sustained, height•Carry: distance, height–Frequency (lift per 5,9,14 sec; 1,2,5,30 min; 8 hr)IE 55318MAW of lift for males (kg)IE 55319Comparison of Strength Testsμ(kg) CV% μ(kg) CV%Static 47.4 8.2 M 42.4 5.1Dynamic 41.9 9.2 F 30.0 10.2Psycho 19.4 5.7Static vs. Dynamic r = 0.47Static vs. Psycho r = 0.35Dynamic vs. Psycho r = 0.14IE 55320Personal Factors Affecting Strength•Gender: F = M⅔•Age: 20-30%↓•Anthropometry–Str vs. W: r = 0.3-0.5–Combo: r = 0.6•Intercorrelations–Compatible r = 0.6•Training–↑ 30-40% over 6 mon.–↑ glycogen,


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PSU IE 553 - Mechanical Work Capacity Evaluation

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