10. Anthropometry and Work-Space Design

고려대학교 산업공학과

IMEN 368 인간공학 II

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



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

1. determine the user population (the intended users)2. determine the relevant body dimensions3. determine the percentage of the population to be accommodated

design for extremes design for adjustable range design for the average

4. determine the percentile value of the selected anthropometric dimension lower-limit dimension upper-limit dimension

5. make necessary design modifications to the data from the anthropometric tables6. use mock-ups or simulators to test the design



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

1. adjusting the workplace2. adjusting the worker position relative to the workplace3. adjusting the workpiece4. 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 distance1. frequency of use principle2. importance principle



3. sequence of use principle4. consistency principle5. control-display compatibility principle of colocation6. clutter-avoidance principle7. 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



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



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)



BIOMECHANICAL MODELS musculoskeletal system as a system of mechanical links bones and muscles act as a series of levers Newton’s 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



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), golfer’s elbow (medial epicondylitis) CTDs at the shoulder -- Rotator cuff irritation, swimmer’s shoulder, pitcher’s 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



Hand-tool Design1. Do not bend the wrist2. shape tool handles to assist grip3. provide adequate grip span4. provide finger and gloves clearances



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 and CP to create high energy phosphate compounds through

aerobic and anaerobic metabolism (fig 12.2) AnaerobicA. Phosphagen (ATP - CP) System

1. ATP ADP + P + Energy 2. CP C + P + Energy (rebound ADP and P to ATP)



B. Anaerobic Glycolysis System – oxygen debt, not efficient1. Glucose (C6H12O6)n Lactic acid (2C3H6O3) + Energy2. Energy + 3ADP + 3P 3ATP

Aerobic Reaction – steady state1. C16H32O2 (carbohydrates and fatty acids) + 23O2 16CO2 + 16H2O + Energy2. 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 ( 혈소판 ) – 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)



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

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)



The Respiratory System 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



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



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”



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



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

10. Anthropometry and Work-Space Design

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