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:

 Demonstrate working knowledge of anthropometric methods

 Demonstrate ability to utilize anthropometric data in a design

scenario

 Describe various factors that can affect anthropometric

measures

 Demonstrate working knowledge of human strength attributes

 Describe various factors that can affect human strength

ANTHROPOMETRY AND PHYSICAL

ERGONOMICS (CONTD.)

Some Key Terms

 Anthropology: The science of human beings.

 Physical Anthropology: The study of physical

characteristics of human beings.

 Anthropometry: A branch of physical

anthropology dealing with body dimensions and

measurements.

ANTHROPOMETRY AND PHYSICAL

ERGONOMICS (CONTD.)

DIVISIONS OF ANTHROPOMETRY

1. Static anthropometry: Body measurement without

motion (e.g., stature). This measurement helps the

designer "fit" the worker into the workplace.

2. Dynamic anthropometry: Body measurement with

motion (e.g., vertical reach envelopes). This

measurement helps the designer check if worker can

"function" within the workplace.

3. Newtonian anthropometry: Body segment measures for

use in biomechanical analyses (e.g., link lengths, center

of mass, inertial characteristics).

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.

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

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

• 5th percentile to 95th 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 (5th percentile) OR larger male (95th percentile)

• Door frame, shelf height, etc.

4. Design for population average

• Normally not recommended

• Public facilities

• Recommended only when used for a short duration

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

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.

ANTHROPOMETRY AND PHYSICAL

ERGONOMICS (CONTD.)

Engineering

Specifications

Anthropometric

Measure/Reference

Display Height Eye Height

Console Height

(undersurface)

Knee Height

Tool Handle Size Hand Width, Length,

etc.

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.

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.

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

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

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”

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

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

ANTHROPOMETRY AND PHYSICAL

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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

ANTHROPOMETRY AND PHYSICAL

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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 Gender

Body composition Occupation

Regular exercise Ethnic origin

Fatigue Dominant, non-dominant side of

body

Biomechanical factors Clothing and personal equipment

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.

ANTHROPOMETRY AND PHYSICAL

ERGONOMICS (CONTD.)

CASE STUDY 3-1. Evaluating Population

Design Parameters. (Page 41)

CASE STUDY 3-2. Evaluating Population

Accommodation. (Page 42)