10. Anthropometry and Work-Space Design

1. 10. Anthropometry and Work-Space Design • Anthropometry – the study and measurement of human body dimensions • HUMAN VARIABILITY AND STATISTICS • Human Variability • Age Variability • Sex Variability • Racial and Ethnic Group Variability • Occupational Variability • Generational or Secular Variability • Transient Diurnal Variability • Statistical Analysis • Normal Distribution • Percentiles • ANTHROPOMETRIC DATA • Measurement Devices and Methods • height, breadth, depth, distance, circumference, curvature • Civilian and Military Data • civilian -- out-dated and limited

2. Structural and Functional Data • structural data (static data) • taken with the body in standard and still position • functional data (dynamic data) • taken when the body adopts various working postures • Use of Anthropometric Data in Design • determine the user population (the intended users) • determine the relevant body dimensions • determine the percentage of the population to be accommodated • design for extremes • design for adjustable range • design for the average • determine the percentile value of the selected anthropometric dimension • lower-limit dimension – physicalsize of the system, not the human user • upper-limit dimension • make necessary design modifications to the data from the anthropometric tables • use mock-ups or simulators to test the design

3. GENERAL PRINCIPLES FOR WORK-SPACE DESIGN • Clearance Requirement of the Largest users • lower-limit dimension, for the largest users (start with 95 %tile) • Reach Requirement of the Smallest Users • upper-limit dimensions, for the smallest users (start with 5 %tile) • reach envelop (area) – the 3D space in front of a person without leaning forward or stretching • Special Requirement of Maintenance People • AdjustabilityRequirements • adjusting the workplace • adjusting the worker position relative to the workplace • adjusting the workpiece • adjusting the tool • Visibility and Normal Line of Sight • normal line of sight – the preferred direction of gaze when the eyes are at a resting condition • about 10 to 15°below the horizontal plane • Component Arrangement • increase overall movement efficiency and reduce total movement distance • frequency of use principle • importance principle

4. sequence of use principle • consistency principle • control-display compatibility principle of colocation • clutter-avoidance principle • functional grouping principle • functionaland sequence more critical than importance in positioning controls and displays • subjective judgment, link analysis, optimization approach • DESIGN OF STANDING AND SEATED WORK AREAS • Choice Between Standing and Seated Work Areas • standing • frequent movements in a large work area • heavy or large objects or exert large forces with their hands • use of floor mats and shoes with cushioned soles • seated • long-duration jobs • allows for better controlled arm movements, provides a stronger sense of balance and safety, improves blood circulation • leg rooms or leg and knee clearance • adjustable chairs and footrests

5. seat-stand • Work Surface Heights • 5-10 cmbelow elbow level for standing and at elbow level for seated – fig 10.9 • Work Surface Depth • normal work area – a sweep of the forearm without extending the upper arm – fig. 10.10 • maximum – a sweep of the arm by extending the arm from the shoulder • Work Surface Inclination • slightly slanted surfaces (about 15°) for reading • less trunk movement, less bending of the neck • horizontal desk for writing

10. 11. Biomechanics of Work • awkward postures and heavy exertion forces – musculoskeletal problems • low back pain and UECTDs • THE MUSCULOSKELETAL SYSTEM • support and protect body and body parts, maintain posture and produce body movement, generate heat and maintain body temperature • Bones and Connective Tissues • protect internal organs – skull, rib cage • support body movement and activities – long bones of the upper and lower-extremities • Connective Tissues -- tendons, ligaments, cartilage, fascia • joints -- synovial joints, fibrous joints (skull: fibrous tissues), cartilaginous joints (vertebral bones) • no mobility joints, hinge joints, pivot joints, ball and socket joints • Muscles • 400 muscles, 40 – 50% of BW • supply energy and produce body motion • generate heat and maintain body temperature • muscle fibers, connective tissues and nerves • a motor unit – “all-or-none” • muscle contraction – concentric (isotonic), eccentric, isometric contraction • no measuring device for tension in the muscle for muscle strength  torque or moment • static/dynamic muscle strength (isokinetic equipment, psychophysics)

11. BIOMECHANICAL MODELS • musculoskeletal system as a system of mechanical links • bones and muscles act as a series of levers • Newton’s law • Bodysegment not in motion – static equilibrium • The sum of all external forces on an object must be equal to zero • The sum of all external moments on an object must be equal to zero • Single-Segment Planar, Static Model • LOW-BACK PROBLEMS • Low-Back Biomechanics of Lifting • the most vulnerable link because of most distant from the load • L5/S1 • normal range of strength capability of the erector spinal muscle at low back is 2,200 – 5,500N • compression force on L5/S1

12. Seated Work and Chair Design • LBP is common – loss of lordotic curvature in the spine  increase in disc pressure • lordosis and kyphosis • seating – pelvis rotated backward  lumbar lordosis into kyphosis • backrest inclination angle – 110 to 120° • lumbar support – a pad in the lumbar region – thickness of 5cm • arm rest, tiltable seat surface • UPPER-EXTREMILTY CUMULATIVE TRAUMA DISORDER • Common Forms of CTD • Tendon-Related CTD -- tendon pain, inflammation of tendon, tendonitits • Neuritis – tingling and numbing • Ischemia – tingling and numbing at the fingers • Bursitis – inflammation of a bursa • CTDs of the Fingers – vibration-induced white fingers (cold), trigger finger • CTDs of the hand and wrist -- CTS (carpal tunnel syndrome) fig 11.7 • CTDs at the elbow -- Tennis elbow (lateral epicondylitis), golfer’s elbow (medial epicondylitis) • CTDs at the shoulder -- Rotator cuff irritation, swimmer’s shoulder, pitcher’s arm

13. Causes and prevention of CTDs • Repetitive motion, excessive force application, unnatural posture, prolonged static exertion, fast movement, vibration, cold environment, pressure of tools or sharp edges of soft tissues • Non-occupationalfactors • Health condition, wrist size, pregnancy, use of oral contraceptives, sex, age, psychological factors • Prevention through administrative and engineering methods • Worker education, training, appropriate work-rest schedule • Redesign the workplaces and tools • Hand-tool Design • Do not bend the wrist • shape tool handles to assist grip • provide adequate grip span (fig 11.9) • provide finger and gloves clearances

17. (Q) Supposea person is holding a load of 20-kg mass with hands in front of his body and his forearm are horizontal. The load is equally balanced the two hands • W = mg = 20kg*9.8m/sec = 196N • Won-each-hand = 98N • ∑ Felbow = 0 • - 16N – 98N + Relbow = 0 • Relbow = 114N • ∑ Melbow = 0 • - 16N(0.18m) – 98N(0.36m) + Melbow = 0 • Melbow = 38.16N-m shoulder 30° HW: What are the reactive force and moment at shoulder? BW = 78Kg Upper arm = 0.028BW distance from shoulder to elbow = 33cm center of gravity = 15 cm from the shoulder elbow

18. Cervical (7) Thoracic (12) Lumbar (5) Sacrum

19. Clockwise rotational moment: Mload-to-torso (L5/S1) = Wload*h + Wtorso*b Counterclockwise rotational moment: Mback-muscle = Fback-muscle * 5(N-m) ∑ ML5/S1 = 0 Fmuscle * 5 = Wload*h + Wtorso*b Fmuscle = Wload*h/5 + Wtorso*b/5 Torso weight = 350N, Load = 300N (about 30kg) then Fmuscle = 3,800N Normal range of strength capability of the erector spinal muscle is 2,200 to 5,500N Compression force on L5/S1 ∑ F L5/S1 = 0 Fcompression = Wload*cosα + Wtorso*cosα + Fmuscle Suppose α = 55°, torso weight 350N, load = 450N Fcompression = 450*cos 55° + 350*cos 55° + 5000 = 258 + 200 + 5000 = 5458N

25. 12. Work Physiology • MUSCLE STRUCTURE AND METABOLISM • Muscle Structure • primary function – generate force and produce movement • smooth muscle – digestion of food and regulation of the internal environment – no conscious control • cardiac muscle – no conscious control • skeletal muscle – the largest tissue in the body – 40% of body weight • direct conscious control, physical work possible • muscle fibers>myofibrils>sarcomeres (fig 12.1) • sarcomeres – myosin and actin • the sliding filament theory of muscle contraction • Aerobic and Anaerobic Metabolism • Phosphorylation – from ATP (adenosine triphosphate) and CP (creatine phosphate) to create high energy phosphate compounds through aerobic and anaerobic metabolism (fig 12.2) • Anaerobic • Phosphagen (ATP - CP) System • ATP  ADP + P + Energy • CP  C + P + Energy (rebound ADP and P to ATP)  most rapid means of replenishing ATP in the muscle cell

26. Anaerobic Glycolysis System – oxygendebt, not efficient • Glucose (C6H12O6)n Lactic acid (2C3H6O3) + Energy • Energy + 3ADP + 3P  3ATP • Aerobic Reaction – steady state • C16H32O2 (carbohydrates and fatty acids)+ 23O2  16CO2 + 16H2O + Energy • 130 ADP + 130P + Energy  130ATP • THE CIRCULATORY AND RESPIRATORY SYSTEMS • The Circulatory System • Transportation system of the body; it delivers oxygen and nutrients to the tissues and removes carbon dioxide and waste products from the tissues • The Blood • 8% of body weight • red blood cells • transport oxygen and remove carbon dioxide • formed in bone marrow and carries the Hb • white blood cells – fight germs and defend the body against infections • platelets (혈소판) – stop bleeding • Plasma – 90% water10% nutrients and solutes • The Structure of the Cardiovascular Systems • the heart – four-chambered (atrium and ventricle, atrioventricular valves) – fig 12.3 • arteries and veins (one-way valves)

27. the systemic circulation • the left ventricle  aorta  arteries  arterioles  capillaries • venules  veins  superior vena cava (inferior v.c.)  the right atrium • the pulmonary circulation (oxygenation) • the right ventricle  pulmonary arteries to the lung  arterioles  capillaries • venules  veins  pulmonary veins  the left artium • Blood Flow and Distribution • the resistance to flow – blood vessel’s radius and length • systolic pressure – the maximum arterial pressure • diastolic pressure – the minimum • arterioles are the major source to blood flow • cardiac output (Q) – the amount of blood pumped out of the left ventricle per minute • influencedby physiological, environmental, psychological, individual factors • 5 L/min for rest to 25 L/min for heavy work • to increase the cardiac output -- increase HR or stroke volume (SV) • Q (L/min) = HR (beats/min) * SV (L/beat)

28. The Respiratory System • Exchanges oxygen and carbon dioxide with the external environment • The Structure of the Respiratory System • the nose, pharynx (인두), larynx (후두), trachea (기관), bronchi (기관지) • lungs – alveoli (200 mil to 600 mil) • alveolar ventilation – the amount of gas exchange per min. in the alveoli • the muscles of the chest, diaphragm • Lung Capacity • total lung capacity (fig. 12.4) • minute ventilation (volume) – tidal volume x frequency • increasing the tidal volume is more efficient than increasing the breathing frequency • ENERGY COST OF WORK AND WORKLOAD ASSESSMENT • Energy Cost of Work • basal metabolism – the lowest level of energy expenditure to maintain life; a resting person under dietary restrictions for several days and no food intake for 12 hours – 1600 to 1800 kcal/day or 1 kcal/kg/hour • 2400 kcal/day for basal metabolism and leisure and low-intensity everyday nonworking activities • Working metabolism (metabolic cost of work) – increase in metabolism from the resting to the working level • metabolic or energy expenditure rate during physical activity = working metabolism rate (metabolic cost of work) + basal metabolism rate – fig. 12.5

29. physical demand of work • Light – smaller than 2.5 kcal/min – oxidative metabolism • Moderate – 2.5 to 5.0 kcal/min – oxidative metabolism • Heavy – 5.0 to 7.5 kcal/min – only physically fit workers through oxidative metabolism, oxygen deficit incurred at the start of work cannot be repaid until the end of the work • very heavy ( 7.5 to 10 kcal/min), extremely heavy (greater than 10 kcal/min) – even physically fit workers cannot reach a steady state condition during the period of work – oxygen deficit and lactic acid accumulation • Measurement of Workload • Physiological and subjective methods • energy expenditure rate is linearly related to the oxygen consumption rate and to HR • Oxygen Consumption • Energy expenditure rate (kcal/min) = 4.8 kcal/liter * oxygen consumption rate (l/min) • Oxygen consumption = aerobic metabolism during work + anaerobic metabolism during recovery • static work not well reflected in O2 measure • Heart Rate • indirect measure of energy expenditure, not as reliable as O2 consumption rate • resting HR – 60 to 80 beats/min • increase from the resting to the steady state is a measure of physical workload • max HR = 206 – (0.62*age) • max HR = 220 – age

30. Blood Pressure and Minute Ventilation • BP -- not used as often as O2 consumption and HR but more accurate for awkward static posture • minute ventilation (minute volume) – the amount of air breathed out per minute – measured in conjunction with O2 consumption and used as an index of emotional stress • Subjective Measurement of Workload • Borg RPE (Ratings of Perceived Exertion) Scale of 6 to 20 (beats/min) • PHYSICAL WORK CAPACITY AND WHOLE-BODY FATIGUE • Short-Term and Long-Term Work Capacity • Physical work capacity -- a person’s maximum rate of energy production during physical work • the short-term maximum physical work capacity (MPWC) or aerobic capacity – VO2max – heart cannot beat faster and the cardiovascular system cannot supply oxygen – 15kcal/min for healthy male and 10 kcal/min for healthy female • long-term maximum physical work capacity • for continuous dynamic work, 5 kcal/min for male and 3.5 kcal/min for female • Causes and Control of Whole-Body Fatigue • experienced whole-body fatigue around 30 to 40% of maximum aerobic capacity • certainly feel fatigued if the energy cost exceeds 50% of the aerobic capacity because the body cannot reach the “steady state”

31. Causes of fatigue  Accumulation of lactic acid in prolonged heavy work but not found with prolonged moderate work; depletion of ATP and CP, symptom of disease or poor health • engineering methods to reduce the risk of whole-body fatigue – redesign the job and provide job aids • administrative methods(work-rest scheduling) without heat stress • rest period = (PWC – Ejob)/(Erest – E job) • with heat stress • Static Work and Local Muscle Fatigue • Static muscle contractions impede or even occlude blood flow to the working muscles • Rohmert curve – the relationship between endurance and %MVC • EMG and psychophysical scales • Engineering and Administrative methods

32. (the contractile unit of skeletal muscle) Figure12.1 The structure of muscle

34. Pulmonary circulation Systemic circulation Figure12.3 The anatomy of the circulatory and respiratory systems

35. (인두) (후두) (기관) (기관지) (횡경막, 가로막)

36. Figure12.4 Respiratory capacities and volumes

37. working metabolism Resting-level metabolism Figure12.5 The change in total energy expenditure rate as activity level changes

38. BORG’S RATED PERCEIVED SCALE 6 7 VERY, VERY, LIGHT 8 9 VERY LIGHT 10 11 FAIRLY LIGHT 12 13 SOMEWHAT HARD 14 15 HARD 16 17 VERY HARD 18 19 VERY, VERY, HARD 20

40. Figure12.9 Relationship between static muscle endurance time and muscle exertion level