AnthropometryA.H. Mehrparvar

Occupational Medicine DepartmentYazd University of Medical Sciences

Definitions Anthropology:

The science of human beings

Physical anthropology: The study of physical characteristics of human beings

Antropometry: A branch of physical anthropology dealing with body dimensions and measurements.

Introduction the science that deals with the

measurement of size, mass, shape, and inertial properties of the human body

the measure of physical human traits to: determine allowable space and equipment size

and shape used for the work The results are statistical data describing

human size, mass and form.

Considered Factors: agility and mobility Age Sex body size Strength disabilities

Engineering anthropometry: Application of these data to tools, equipment,

workplaces, chairs and other consumer products.

The goal: to provide a workplace that is efficient, safe

and comfortable for the worker

Static anthropometry –body

measurement without motion Dynamic anthropometry -body

measurement with motion Newtonian anthropometry -body

segment measures for use in biomechanical analyses

Divisions of anthropometry

Static Anthropometric Measurements

Static = Fixed or not moving Between joint centers Body lengths and contours Measuring tools: Laser (computer),

measuring tape, calipers

Dynamic Anthropometric Measurements Dynamic = Functional or with movement

No exact conversions for static to dynamic Kromer (1983) offers some rough estimates for

converting static to dynamice.g. Reduce height (stature, eye, shoulder,

hip, etc.) by 3%. Somatography

e.g. A CAD program named SAMMIE e.g. A virtual reality program named dv/Maniken

Scale model mock-up

Designing for 90 to 95 percent of anthropometric dimensions.

Designing for the “average person” is a serious error and should be avoided

Designing for the tallest individuals (95th percentile): leg room under a table

designing for the shortest individuals (5th percentile): reach capability.

Designing “average person”: Supermarket counters and shopping carts

Design Principles Designing for extreme individuals

Design for the maximum population value when a maximum value must accommodate almost everyone. E.g. Doorways, escape apparatus, ladders, etc.

This value is commonly the 95th percentile male for the target population.

Design for the minimum population value when a minimum value must accommodate almost everyone. E.g. Control panel buttons and the forces to operate them.

This value is commonly the 5th percentile female for the target population.

Design Principles, continued Designing for an Adjustable Range

Designing for the 5th female/95th male of the target population will accommodate 95% of the population.

95% because of the overlap in female/male body dimensions (if the male/female ratio is 50/50).

Examples are auto seats, stocking hats Designing for the Average

Use where adjustability is impractical, e.g. auto steering wheel, supermarket check-out counter, etc.

Where the design is non-critical, e.g. door knob, etc.

Designing for Motion Select the major body joints involved Adjust your measured body dimensions to

real world conditions e.g. relaxed standing/sitting postures, shoes,

clothing, hand tool reach, forward bend, etc. Select appropriate motion ranges in the

body joints, e.g. knee angle between 60-105 degrees, or as a motion envelope. Avoid twisting, forward bending, prolonged

static postures, and holding the arms raised

7 Steps to Apply Anthropometric Data Identify important dimensions, e.g. hip breadth for a

chair seat Identify user population, e.g. children, women, Iran

population Determine principles to use (e.g. extremes, average,

adjustable) Select the range to accommodate, e.g any%, 90%,

95% Find the relevant data, e.g. from anthropometric data

tables. Make modifications, e.g. adult heavy clothing adds ~4-6

linear inches. Test critical dimensions with a mock-up, user

testing, or a virtual model

Variability - three areas Anthropometric data show

considerable variability stemming from the following sources:

Poor data Interindividual variability Intraindividual variability

Poor data Variability in measurements arise from:

Population samples Using measuring instruments Storing the measured data Applying statistical treatments

Intraindividual variability Changes in time Size and body segment size, change with a

person’s age -some dimensions increase while others decrease

Interindividual variability Individual people differ in: arm length stature and weight therefore population samples are usually

collected from cross sectional studies

Long-term trends Change in body size by time and in

different generations

Areas of anthropometry Anthropometry can include just general

measurements of dimension of body segments Lengths Circumferences (girths) Breadths (width) depths Body composition

In biomechanics, mostly concerned with BSIPs (Body Segment Inertial Parameters) Segment mass Center of mass Moment of inertia

Inertial Parameters Typical biomechanical analyses require

the following: Segment mass Location of center of mass Moment of inertia

These properties of a rigid body are often referred to as Inertial Parameters

Body Segments Divide the body into defined rigid bodies, for

which we know or can determine the inertial properties

Many different ways to divide the body Most common (14 segments):

Head Trunk Upper arm Forearm Hand Thigh Shank Foot

Body Segment Model

X

Y

(Xheel, Yheel)(XT,YT)

(XK,YK)

(XH,YH)

(XA,YA)

“Digitizing”

Rigid Body Analysis Rigid Body

A body made of particles (points), the distances between which are fixed

What is the basic assumption? The human body segments are rigid links Therefore human body can be modeled as a

series of rigid bodies (link segments)

Rigid Body Model

Body Weight (N) = mg

VGRF

Friction

Air Resistance

The human body is modeled as a linked system of rigid bodies

Free Body Diagram Diagram of the essential elements of the

system Segments and Axes of interest Forces acting on the system

Effort and resistance forces Weights of limbs or segments Line and point of application for each force

Force Arms (moment arms) Perpendicular distance from line of force

application to axis of rotation Moment Direction (+/-)

Equilibrium and Static Analysis System is not moving or acceleration is

constant Static Equilibrium

No motion, thus no acceleration So opposing forces are equal

Rigid Body Diagram Free Body DiagramFree Body Diagram Drawing a mechanical picture of the system or

object Example: Muscle-Lever Diagram

Muscle-Lever Diagram Muscle Diagram

Bones Muscles Motion

Lever Diagram Direction Force (direction) Axis Resistance (direction)

Static Analysis Uses the equations of equilibrium across

various postural positions Allows the determination of:

Maximum or minimum muscle forces or moments for a given posture or joint position and load

Shear or injurious forces across joints in a given positional load or task (e.g. lifting)

How body postures affect joint loads Resultant joint moments and forces

Conditions for EquilibriumSum of all horizontal forces must be zero

Fx = 0 Fy = 0

Sum of all vertical forces must be zeroFz = 0

Sum of all moments about the axis (joint) in each plane must be zero

M = 0

Free-body Diagram – The System

The Free-body Diagram

Upper Arm Segment Forearm Segment

Illustration of the essential elements of a system

More Key Terms Moment of Inertia

The resistance of a body to rotation about a given axis

I = Σ mi · ri2

I – moment of inertia about a given axis np – number of particles making up rigid body mi – mass of particle ri – distance between particle and axis

i = np

i = 1

Whole Body Center of Mass Mass – measure of the amount of matter

comprising an object (kg) Center of Mass – location for which mass

of a body is evenly distributed It is the point about which the sum of

torques is equal to zero The point about which objects rotate when

in flight Allows simplification of entire mass

particles into a mass acting through a single point

Center of Mass

0 cmM

Calculation of Segment Massm = Σ mi

m is the total mass mi is the mass of a segment or part Ex. If we have 3 parts or sections, then

m = Σ mi = m1 + m2 + m3

Mass of segment mi = ρi·Vi (density times volume) So… m = ρ Σ Vi (assumes uniform density)

i = 1

n

i = 1

3

i = 1

n

Multi-segment Systems x0 = (m1x1 + m2x2 + m3x3) / M

y0 = (m1y1 + m2y2 + m3y3) / M

(x0,y0) is the COM position for the whole

Mass Moment of Inertia M = I·α

M is moment (Nm) α is the angular acceleration I is constant of proportionality (inertia)

Resistance to change in angular velocity Recall: I = m.r2 (r is the moment arm)

I = m1·x12 + m2·x2

2 + m3·x32

I = Σ mi·xi2

A mass closer to the axis – Less effect A mass further from the axis – Greater effect

Segment and WBCOM Relation

~ ♀55% BH ~ ♂56-57% BH

Benefits of Understanding COM Parabolic flight of a projectile

Jump, aerials, hang time Running performance

Vertical oscillation of COM Manipulation of COM for greater impulse

Long jump, leap Mechanical Stability

Base of Support (BOS) Low COM - STABILITY High COM - MOBILITY

Stability Factors that influence stability

Base of Support

Center of Mass Location

Mass

Whole Body Center of Mass Computation of whole body COM

Where: CMWB x or y : Location of whole body COM in x or y plane MWB : Mass of whole body Mi : Mass of ith segment CM xi or yi : Location of COM of ith segment in x or y

direction

Whole Body Center of Mass For analysis…the person is often divided into

many parts (each considered a rigid body) We may want to know the center of mass of

the entire system Need:

Masses of each of the segments Locations of the centers of mass of each segment

Whole body center of mass position is equivalent to a weighted mean of all the parts

Whole Body Moment of Inertia May have moments of inertia of segments

From tables or whatever Want moment of inertia of the whole body

about it’s COM Useful when analyzing aerials (flight)

What we need: Masses of the segments Locations of segment COM Location of whole body (system) COM Moments of inertia of each segment about the

whole body COM The moments of inertia can be summed

once they are all about the same axis

Problem So…how do we determine inertial

parameters of limb segments in a live subject?

Answer:Amputate

Determination of COM Position So, since we can’t just lop off peoples

limbs… Typically use tables and regression

equations from previous studies: Dempster, 1955 Clauser et al., 1969 Chandler et al., 1975 Vaughan et al., 1992

Measures Mostly simple measures do the trick

Some are more complicated if the measures serve as a guide for man-machine interface requiring a person to perform a task Kinetics and kinematics are typically needed

Get an idea of ROM, height requirements etc. Masses, moments of inertia and their locations

Locating the COM of a Body Segment In case you can’t get permission to

amputate… Early Methods:

Suspension Segmentation (uses tables of regression

equations) Reaction (balance) Board

Advantages and disadvantages for each?

Methods of Measurement Model segments as sticks (1D)

1 measure (length) Model segments as rectangles (2D)

2 measures (length and breadth) Model segments as geometric solids (3D)

2-3 measures (length and circumference at ends) Model segments as series of geometric

solids More measures (segmented lengths and

circumferences)

Suspension Cut off limb Sever, Suspend and Swing

Limb is amputated, weighed (mass), and measured Hung and swung, an object will behave as a pendulum The farther away or greater the moment of inertia, the

slower the swing… Do this enough times and you create data sets that you

can do statistics on and create regression tables Advantage:

Extremely accurate Disadvantage:

Potentially painful, as you would have to amputate the limb

Not to mention the difficulty in getting institutional permission to cut off peoples legs…

Segmentation Uses regression equations based on various

segmentation techniques (e.g. cadaver studies or imaging) Use anatomical landmarks to mark segment ends Measure distance up from origin point (e.g. foot

sole)

Segmentation Could involve amputation, but typically just

involves the use of the regression tables Such tables are created from all kinds of previous

study and data sources: Cadaver Imaging Modeling

Advantages: Simple, quick and easy Everyone does it (popular and accepted)

Disadvantages: Not necessarily accurate to individual or groups

of different gender (e.g. females), ethnicity (e.g. blacks, Asian), age (e.g. young), or status

Classic Cadaver Studies Dempster (1955)

8 male cadavers Age (52-83y), Mass (49-72kg), Stature (1.59-1.86m) Segment COM as % segment length or body height Segment mass as % body mass Tissue density

Clauser et al. (1969) 13 male cadavers Age (28-74y), Mass (54-88kg), Stature (1.62-1.85m) Segment COM as % segment length or body height Segment mass as % body mass Segmental moments of inertia

Chandler et al. (1975) 6 male cadavers Age (45-65), Mass (51-89kg), Stature (1.64-1.81m) Segment COM as % segment length Segment mass as % body mass Segmental moments of inertia

Major Cadaver Studies

Author(s)Cadavers(#, gender)

Age (y)

Body Mass(kg)

Stature(m)

Dempster (1955)

8 male52 – 8349 - 721.59 - 1.86

Clauser et al. (1969)

13 male28 - 7454 – 881.62 - 1.85

Chandler et al. (1975)

6 male45 - 6551 - 891.64 - 1.81

*There are other cadaver studies – but these are the classics

Problems with Using Cadaver Data Storage Age range Cause of death Applicability to live population (especially

sports or athletic populations) Applicability to other genders and ethnic

populations Variation in dissection techniques

Reaction Board Scale and Balance (Reaction) Board

Measure and weigh board (upright) Place board end on pivot (axis) and the other end on the

scale (reaction) Get scale reading (reaction force of board)

Person lays on board with feet at the axis end and head towards scale

Get new scale reading (reaction force of board and body) Calculate COM of person and board from summing the

moments about the axis, with scale reading as a reaction force

Advantages: Accurate to your subject Not too complicated calculations Not dependent upon cadaver data for density values

Disadvantages: Need a few people to do it Equipment required A bit time consuming Can’t get small limb masses or COM’s (scale sensitivity)

Reaction Board - Concept

Mass Moment of Inertia M = I·α

M is moment (Nm) α is the angular acceleration I is moment of inertia (constant of proportionality)

Resistance to change in angular velocity Recall: I = m·r2 (r is the moment arm)

I = m1·x12 + m2·x2

2 + m3·x32

I = Σ mi·xi2

A mass closer to the axis – Less effect A mass further from the axis – Greater effect

Moments and Center of Mass Moment of Force

Measure of the tendency of a force to cause rotation of an object about an axis

M = F · ┴d

Recall: ┴d is called the “moment arm” Perpendicular distance from the axis of rotation to

the line of force application

┴dF

Moments and Center of Mass

Positive Moment Counterclockwise (CCW) rotation about an axis

Negative Moment Clockwise (CW) rotation about an axis

Static Equilibrium No rotation about an axis

1. No moments acting on the object2. Minimum of 2 moments, which summed equal 0 Nm.

Σ M = 0Σ F = 0

Reaction Board Based on moments of force in static equilibrium

Ms

MB

MB

Ms

MP

- -

+

+

+

-

Determination of Whole Body COM

1. Suspension2. Segmentation (Regression Equations)

Imaging techniques (e.g. Zatsiorsky et al., 1990)

Cadaver experiments (e.g. Dempster, 1955) Geometric solid modeling (e.g. Hinrichs,

1985)3. Reaction Board Technique Advantages and disadvantages of each

Other BSIP Techniques1. Simple statistical model (e.g. Dempster,

1955)

2. Complex statistical model (e.g. Hinrichs, 1985)

3. Geometric models (e.g. Hanavan, 1964)

4. Imaging Techniques (e.g. Martin et al., 1989)

COM Techniques Based on Cadaver Studies Suspension

Amputate limbs Weigh Suspend and swing to obtain moment of inertia about

all 3 axes. Segmentation

Amputate limbs (or somehow isolate limbs – imaging) Weigh (mass) and submerge in water (volume and

density) Balance or hang to determine center of mass location

Simple Statistical Model Dempster (1955) dissected 8 male

cadavers ranging in age from 52 to 83 years

Measures:1. Masses of body segments expressed as % of

total body mass e.g. mass of foot is 1.45% body mass

2. Location of center of mass expressed as a % of segment length e.g. com of thigh is located 43.3% along the length of

the thigh from the proximal end

Complex Statistical Model Hinrichs (1985) based his equations on the

data from the 6 male cadavers dissected by Chandler et al. (1975)

Moments of inertia of body segments computed using regression equations containing one or more measurements on segment of interest e.g. Transverse moment of inertia of shank

about com

Geometric Solid Models To avoid dependence

on cadaver data, model segments as series of geometric solids

Although we are still dependent upon cadaver studies for the tissue density

Geometric Solid Models So a cylinder is a

simple shape which can represent the thigh or foot…

Geometric Solid Models Hanavan (1964) was one of the first to

develop such a model Truncated cones (e.g. limbs) Spheres (e.g. hands) Cylinders (e.g. trunk)

Hanavan’s Geometric Model

15 segments Cones Spheres Cylinders

Geometric Solid Modeling

Geometric Solid Modeling

Imaging Techniques Medical imaging Basis (theory):

Beam (e.g. radiation) passes through substance (tissue), beam diminishes in relation to the density of the tissue

Thus, get shape of the segments and tissues Techniques:

Gamma mass scanning (slight dose of radiation)

Computer Tomography (CT) Magnetic Resonance Imaging (MRI)

Imaging Techniques Martin et al. (1989) used MRI to determine

the inertial parameters of 8 baboon cadaver arm segments, then compared these values with physical measures.

ParameterMean Difference

SD

Volume (m3 or l)6.35.0Density (kg/volume)0.03.1Mass (kg)6.72.8COM (m)-2.48.2I (transverse, kgm2)4.43.0

Imaging Techniques Problems:

Equipment not generally available Expensive Possible exposure to radiation (e.g. gamma

mass) Data reduction is time consuming

Advantages: Subject specific parameters Equipment is becoming more generally

available

Segment Length % body

height

Winter, 1990

Segment Mass and COP

Winter, 1990

Segment Mass and COP

Winter, 1990

Segment Mass and COP

Winter, 1990

Important body dimensions