10. Anthropometry and Work-Space Design

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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

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• 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
• upper-limit dimension
• make necessary design modifications to the data
  from the anthropometric tables
• use mock-ups or simulators to test the design

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• 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
• Adjustability Requirements
• 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 15below the horizontal plane
• Component Arrangement
• increase overall movement efficiency and reduce
  total movement distance
• frequency of use principle
• importance principle

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• sequence of use principle
• consistency principle
• control-display compatibility principle of
  colocation
• clutter-avoidance principle
• functional grouping principle
• functional and 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

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• seat-stand
• Work Surface Heights
• 5-10 cm below 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

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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, fibulous joints
  (skull fibulous 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
• concentric 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)

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• BIOMECHANICAL MODELS
• musculoskeletal system as a system of mechanical
  links
• bones and muscles act as a series of levers
• Newtons law
• Body segment 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

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• 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)
• CTDs at the elbow -- Tennis elbow (lateral
  epicondylitis), golfers elbow (medial
  epicondylitis)
• CTDs at the shoulder -- Rotator cuff irritation,
  swimmers shoulder, pitchers arm
• 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

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• Hand-tool Design
• Do not bend the wrist
• shape tool handles to assist grip
• provide adequate grip span
• provide finger and gloves clearances

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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 fibersgtmyofibrilsgtsarcomeres (fig 12.1)
• sarcomeres myosin and actin
• the sliding filament theory of muscle contraction
• Aerobic and Anaerobic Metabolism
• Phosphorylation from ATP and CP 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)

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• Anaerobic Glycolysis System oxygen debt, 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
• 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 (???) stop bleeding
• Plasma 90 water 10 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)

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• 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 vessels 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
• influenced by 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)

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• The Respiratory System
• The Structure of the Respiratory System
• the nose, pharynx (??), larynx (??), trachea
  (??), bronchi (???)
• 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

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• 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 (0.62age)
• max HR 220 age

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• 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 persons 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

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• 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

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• BORGS 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

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