Anthropometry

1
Chapter 3

• Anthropometry

2
Anthropometry

• Deals with the measure of size, mass, shape and
  inertial properties of the human body segments.

3
Biomechanical Models

• Facilitates prediction of a bodys response and
  the design of the workspace interface
• Physical
• crash test dummies

4
Biomechanical Models

• Facilitates prediction of a bodys response and
  the design of the workspace interface
• Physical
• crash test dummies
• Mathematical
• Joint moment of force

5
Biomechanical Models

• Facilitates prediction of a bodys response and
  the design of the workspace interface
• Physical
• crash test dummies
• Mathematical
• Joint moment of force

6
Biomechanical Models

• Facilitates prediction of a bodys response and
  the design of the workspace interface
• Physical
• crash test dummies
• Mathematical
• Joint moment of force

7
Biomechanical Models

• Facilitates prediction of a bodys response and
  the design of the workspace interface
• Physical
• crash test dummies
• Mathematical
• Joint moment of force

8
Measurement of Body-Segment Physical Properties

• Segments defined by bony prominence (landmarks)
  (fig 3.2)
• Human body system of rigid links
• known physical size and form
• connected at identifiable joints

9
Caveat Body-segment links

• No joint in the human body is a simple
  single-axis hinge joints, but are considered so
  in many analyses (1 Degree of Freedom)
• Assume
• segments are rigid links
• joints are frictionless and hinged

10
Body-segment links

• Link lengths can be defined as the distance
  between projected centers
• Resulting error in link length estimate is lt 5

11
Body-segment links

• Acceptable degree of model simplification reflect
  analysis goal
• Assumptions valid for most analyses
• Crash test dummies require consideration of joint
  structure, ligaments, muscle response, organs,
  etc.
• Injury risk (Lives!!) depends on the validity of
  the model

12
Average Segment Lengths as Proportion of Total
Body Height (TBH)see Table 3.7
13
Body-segment mass and weight

• The mass of the body segments adds additional
  stresses to the body beyond those exerted by
  external forces (resistance to acceleration)
• These weight related stresses can be of
  considerable magnitude in certain postures (a
  force)

14
Inertia

• Resistance of an object to changing its current
  state of motion.

15
Body-segment inertial properties

• When a segment can translate and/or rotate during
  activity, the inertial properties of the segment
  must be considered in the analysis

16
Two inertial properties to consider

• Mass resistance to linear acceleration
• Moment of Inertia resistance to angular
  acceleration

17
Conversions

• Mass (kg) to Weight (lbs) multiply by 2.2
  (downward)
• Mass (kg) to Weight (N) multiply by 9.81
  (downward)
• Weight (lbs) to Weight (N) multiply by 4.45

18
Body-segment mass and weight

• Body segment mass (weight) can be expressed as a
  proportion of whole-body mass (weight) without
  great loss of accuracy
• TBM total body mass
• Many sources exist (see p41 in text)

19
Table 3.4, p41

• Recommended Values for Percentage distribution of
  total body weight
• Grouped segments, of total body wt
• Head and neck 8.4
• Torso 50
• Total arm 5.1
• Total leg 15.7

20
data from Winter (1989) based on Dempster
(1956) data (overhead)

• Percent distribution of total body mass
• Grouped segments of total body wt
• Head and neck 8
• HAT 68
• Total arm 5
• Total leg 16

One of the most common sources for anthropometric
data.
21
Winter table
22
Winter table (contd)
23
Example

• TBM of individual is 82 kg (180 lbs)
• 82 kg x -9.81 804 Newtons
• What is mass of upper body?
• from Winter table HAT (head-arms-trunk) 67.8
  of TBM
• Calculate (82 kg) x (0.678) 55.6 kg
• 180 lbs x 0.678 122 lbs
• 804 N x 0.678 545 Newtons

24
Body segmentcenter of mass location

• Insufficient to know only the mass (weight) of a
  body segment to perform an analysis
• Must locate the center of mass for each segment
  (and the entire body)
• single point mass
• point of application of the gravitational force
• See Table 3.5 p43, Table 3.13 p.48
• Better off Winter overhead

25
Winter table
26
Example

• Arm of individual is 51 cm (20 inches) long
• 0.51 m long
• Locate Center of mass
• from Winter table 0.53 (53 of arm length from
  the proximal end)
• Calculate (0.51 m) x (0.53) 0.27 m from the
  proximal end of arm

27
Importance

• Knowledge of
• mass center location in segment
• TBM (weight)
• link length
• sufficient input for static analysis to calculate
  forces and moments at each joint for a given body
  posture.

28
Draw a FBD of Arm (60 inches, 215 pound person)
29
Angular inertial properties

• This property is referred to as
• Inertia (linear motion)
• moment-of-inertia (angular motion)
• not only mass, but mass distribution
• Varies according to Axis
• Varies according to mass distribution

I m r2
30
Moment of Inertia

• greater the moment of inertia
• greater inertial load
• Greater joint stress

Example flexed vs straight elbow
31
Anthropometric Data for Biomechanics Studies in
Industry

• anthropometric data defines the reach and space
  requirements of a specified population or
  equipment user
• modeling and simulation
• important consideration for workplace design

Making anthropometric measurements in the modern
world
32
Workplace Analyses

• The book includes tables of PERCENTILE data for
  segment lengths, weights, mass-center location,
  and moment of inertia based on the general
  population.

95
z 1.645
5
z - 1.645
50
33
(No Transcript)
34
Example application of Percentile Tables ( Table
3.8 3.9)

• Table 3.8 Segment lengths as TBH
• Table 3.9 the mean (50th), 5th and 95th
  percentile population heights.
• design must strive to accommodate the 5th to 95th
  percentiles (M F)
• Importance hand tools, workstation surfaces and
  seat design

35
Example Using USAF men and women

• New pliers with span of 11 cm (4.3)
• USAF women average ht 162.1 cm
• USAF men average ht 177.2 cm
• Calculate average hand length (0.108 x height)
• Females 162.1 x 0.108 17.5 cm (6.9 )
• Males 177.2 x 0.108 19.0 cm (7.5)

36

• Male and female differences
• Racial differences
• (US vs Japanese)
• Specific population
• (ie source military, NASA, civilians)
• number of subjects
• source of variability (SD)
• (ie NASA vs civilians)

37
Summary

• Knowledge of anthropometry is important
• Anthropometrics is basis of models
• mass, length, and center of mass of segments
• Design must accommodate 5th to 95th
• appropriate sex, race, specific population
• Will use the tables with future analysis