OCCUPATIONAL ERGONOMICS Chapter 3 ANTHROPOMETRY AND PHYSICAL ERGONOMICS
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OCCUPATIONAL ERGONOMICS Chapter 3 ANTHROPOMETRY AND PHYSICAL ERGONOMICS
ANTHROPOMETRY AND PHYSICAL ERGONOMICS Learning Objectives At the conclusion of this chapter, learners will be able to do the following: n Demonstrate working knowledge of anthropometric methods n Demonstrate ability to utilize anthropometric data in a design scenario n Describe various factors that can affect anthropometric measures n Demonstrate working knowledge of human strength attributes n Describe various factors that can affect human strength 2
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) Some Key Terms Anthropology: The science of human beings. n Physical Anthropology: The study of physical characteristics of human beings. n Anthropometry: A branch of physical anthropology dealing with body dimensions and measurements. n 3
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) DIVISIONS OF ANTHROPOMETRY 1. 2. 3. Static anthropometry: Body measurement without motion (e. g. , stature). This measurement helps the designer "fit" the worker into the workplace. Dynamic anthropometry: Body measurement with motion (e. g. , vertical reach envelopes). This measurement helps the designer check if worker can "function" within the workplace. Newtonian anthropometry: Body segment measures for use in biomechanical analyses (e. g. , link lengths, center of mass, inertial characteristics). 4
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) SOURCES OF ANTHROPOMETRIC DATA 1. Military (U. S. and others) 2. U. S. Public Health Service 3. British Office of Population Censuses and Surveys (OPCS) 4. Other national-based surveys 5. Industrial labs. 5
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) FACTORS AFFECTING BODY DIMENSIONS 1. Human variation due to: - Age Gender Ethnic origin Long-term population shifts 2. Personal equipment and clothing 6
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) USE OF ANTHROPOMETRIC DATA 1. Design for the individual: Best design, but can be expensive. 2. Design for adjustable range • 5 th percentile to 95 th percentile of the user population • Preferred for multiple users, but can be expensive also • Make special accommodation for those outside range 3. Design for population extremes • For smaller female (5 th percentile) OR larger male (95 th percentile) • Door frame, shelf height, etc. 4. Design for population average • Normally not recommended • Public facilities • Recommended only when used for a short duration 7
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ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) Evaluating Anthropometric Design Parameters From Standard-Normal statistical distribution (bell curve): Z = (x - µ)/σ (Eq. 3 -1) where, Z = standard normal value corresponding to population cumulative density µ = average, or mean of dimension for population σ = standard deviation of population x = value of measured dimension 10
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ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) Analysis/Design Objectives 1. Determining design specification values. 2. Evaluating population accommodation. Summary of General Design Procedures Step 1. Select anthropometric measure(s) that directly correspond to the required engineering and/or architectural design specification. 12
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) Engineering Specifications Display Height Anthropometric Measure/Reference Eye Height Console Height (undersurface) Tool Handle Size Knee Height Hand Width, Length, etc. 13
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) Step 2. For each matched pair identified in Step 1, determine whether the design must fit a singular population percentile, or a range along that dimension. Step 3. Apply any necessary correction factors. Step 4. Combine all selected design specifications into a “model” and check for feasibility. 14
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) MUSCULAR STRENGTH Strength is defined as the ability of a muscle group(s) to generate maximal voluntary torque about a joint. A key word in this definition is “voluntary, ” as strength data is collected using protocols designed to elicit subjective (e. g. , psychophysical) responses. Typically then, the phrase “maximum voluntary contraction” (MVC) is used to describe the response recorded by an external instrument during a strength testing protocol. 15
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) FACTORS AFFECTING MUSCULAR STRENGTH 1. Biological and personal factors • • • Age Gender Body composition Hand preferences Biomechanical factors (mechanical advantage) Ethnic origin Fatigue Exercise Diet, overall health 16
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) 2. Environmental factors • • Altitude Acceleration 3. Psychological factors • • Motivation Emotional state 4. Occupational factors • • Task characteristics - posture, coupling, duration, frequency, etc. Clothing and personal equipment 17
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) Hand Strength § § - Grip - Pinch § § § Lateral (Key) Chuck (three fingers), and Tip In occupational setting, hand force can be broadly classified into “Power” and “Precision” 18
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ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) TYPES OF MUSCULAR CONTRACTION 1. Static Contraction Isometric • • contraction where the muscle does not change length no external work done, energy spent, fatigue sets in quickly example: pushing against a wall 21
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) TYPES OF MUSCULAR CONTRACTION (contd. ) 2. Dynamic Contraction Isokinetic • • contraction of muscle at constant velocity normally associated with external resistance being measured at constant velocity, rather than muscle fibers proper example: peak force measured of arm curl at 30 deg/sec velocity using Cybex machine 22
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) Isoinertial • mass constant, but velocity and muscle length change, tension not constant. example: lifting a constant weight Isotonic • • contraction where the muscle shortens but the tension remains constant work done, energy spent example: holding barbells 23
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) RANGE OF JOINT MOTION Range of motion is defined as the maximal angle range between two body segments, or between a body segment and reference plane, measured about a common joint. FACTORS AFFECTING RANGE OF JOINT MOTION Age Body composition Regular exercise Fatigue Biomechanical factors Gender Occupation Ethnic origin Dominant, non-dominant side of body Clothing and personal equipment 24
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ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) Bio-instrumentation To measure body segment lengths, a set of anthropometric calipers is used. A handgrip dynamometer (Jamar or Lafayette) is used to measure handgrip strength and a pinch dynamometer is used to measure pinch strength. The protocol used to measure has been discussed earlier. 26
ANTHROPOMETRY AND PHYSICAL ERGONOMICS (CONTD. ) CASE STUDY 3 -1. Evaluating Population Design Parameters. (Page 41) CASE STUDY 3 -2. Evaluating Population Accommodation. (Page 42) 27
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