Anthropometrics I

Rad Zdero, Ph.D.University of Guelph

Outline

• Anatomical Frames of Reference• What is “Anthropometrics”?• Static Dimensions• Dynamic (Functional) Dimensions• Measurement of Dimensions

Planes of Motion

Transverse Plane Frontal Plane Sagittal Plane

Anatomical Frames of Reference

Top View (Transverse Plane)

Anterior

PosteriorLateral Lateral

Medial Medial

Relative Position

A

B

C

A

BC Point A is Proximal to point B

Point B is Proximal to point CPoint A is Proximal to point C

Point C is Distal to point BPoint B is Distal to point APoint C is Distal to point A

Relative Position

What is “Anthropometrics”?

• The application of scientific physical measurement techniques on human subjects in order to design standards, specifications, or procedures.

• “Anthropos” (greek) = person, human being• “Metron” (greek) = measure, limit, extent• “Anthropometrics” = measurement of people

Static Dimensions• Definition: “Measurements taken when the

human body is in a fixed position, which typically involves standing or sitting”.

• Types• Size: length, height, width, thickness

• Distance between body segment joints

• Weight, Volume, Density = mass/volume

• Circumference

• Contour: radius of curvature

• Centre of gravity

• Clothed vs. unclothed dimensions

• Standing vs. seated dimensions

Static Dimensions

[Source: Kroemer, 1989]

Static Dimensions

• Static Dimensions are related to and vary with other factors, such as …

• Age• Gender• Ethnicity• Occupation• Percentile within Specific Population Group• Historical Period (diet and living conditions)

Static DimensionsAGE

Age (years)0 10 20 30 40 50 60 70 80

Lengthsand

Heights

Static DimensionsGENDER

[Sanders &McCormick]

Static Dimensions

ETHNICITY

[Sanders &McCormick]

Static Dimensions

OCCUPATION

e.g. Truck drivers are taller & heavier than general population

e.g. Underground coal miners have larger circumferences (torso, arms, legs)

Reasons• Employer imposed height and weight restrictions• Employee self-selection for practical reasons• Amount and type of physical activity involved

Static DimensionsPERCENTILE within Specific Population Group

Normal or GaussianData Distribution

No. ofSubjects

5th percentile = 5 % of subjectshave “dimension”below this value

50 %95 %

Dimension(e.g. height,weight, etc.)

Static DimensionsHISTORICAL PERIOD(Europe, US, Canada, Australia)

Decade1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990

Increasein

AverageAdultHeight(inches)

4 inch increase in 8 decades

Dynamic (Functional) Dimensions• Definition: “Measurements taken when the human body is

engaged in some physical activity”.• Types: Static Dimensions (adjusted for movement),

Rotational Inertia, Radius of Gyration• Principle 1 - Estimating

• Conversion of Static Measures for Dynamic Situations• e.g. dynamic height = 97% of static height• e.g. dynamic arm reach = 120% of static arm length

• Principle 2 - Integrating• The entire body operates together to determine the

value of a measurement parameter• e.g. Arm Reach = arm length + shoulder movement

+ partial trunk rotation and + some back bending + hand movement

Dynamic (Functional) Dimensions

[Source: North, 1980]

Measurement of Anthropometric

Dimensions

• Segments are modeled as rigid mechanical links of known physical shape, size, and weight.

• Joints are modeled as single-pivot hinges.• Standard points of reference on human body are

defined in the scientific literature and are not arbitrarily used in ergonomics

• Less than 5% error by this approximation

Segment Lengths: Link/Hinge Model

L

Joint or Hinge

Segment

Segment Lengths: Link/Hinge Model

Segment Density

where

D = density [g/cm3 or kg/cm3]

M = mass [g or kg]

V = volume [cm3 or m3]

W = weight [N or pounds]

g = gravitational acceleration = 9.8 m/s2

D = M / V = (W/g) / V

Segment Density

Double-tanksystem for measuringdisplaced volumeof human bodysegments on livingor cadaver subjects.Using standardizeddensity tables, the mass can then be calculated usingD = M / V.

[source: Miller & Nelson, 1976]

• Important to know the location of the effective center of gravity (or mass) of segments

• Gravity actually pulls on every particle of mass, therefore giving each part weight

• For the body, each segment is treated as the smallest division of the body

• Can obtain C-of-G for individual segments or group of segments

• C-of-G usually slightly closer to the “thicker” end of the segment

Segment Center-of-Gravity

[Kreighbaum & Barthels, 1996]

Segment

C-of-G

9 6 3 963distance

Force 3020

10

3020

10

[adapted from Kreighbaum & Barthels, 1996]

C-of-G Line30

2010

3020

10

9 6 3 963

Force

distance

Different weightor mass distributionscan have the sameC-of-G

Segment Centers-of-Gravity shown as percentage of segment lengths [Dempster, 1955].

Balance Method• Weight (force of gravity) & vertical reaction force

at the fulcrum (axis) must lie in the same plane.

[Kreighbaum & Barthels, 1996]

Segment Center-of-Gravity

C-of-G line

C-of-G line

C-of-G line

Reaction Board Method 1 – Individual Segments

Segment Center-of-Gravity

[LeVeau, 1977]

Sum all moments around pivot point ‘O’ for both cases:-WX – SL – W2L2 = 0-WX’ – S’L – W2L2 = 0 Subtract equations and rearrange to obtain the exact location (X) of C-of-G for the shank/foot system:

X = {L(S - S’)/W + X’}

O

O

W2

W2

L2

L2

Reaction Board Method 2 – Group of Segments

[Hay and Reid, 1988]

Segment Center-of-Gravity

Weigh Scales

Support Point

C-of-G

Suspension Method• Determine pivot

point which balances the object in 2D plane

• Use frozen human cadaver segments

[Hay & Reid, 1988]

Segment Center-of-Gravity

Multi-Segment Method• Imagine a body composed of three segments, each with the

C-of-G and mass as indicated• sum of Moments of each segment mass about the origin =

Moment of the total body mass about the origin• mathematically: MO = MA + MB + MC = MA+B+C

O 4 6 82

30 N 10 N 5 N

A B C

distance

Segment Center-of-Gravity

Multi-Segment Method Example – Leg at 90 deg

A leg of is fixed at 90 degrees. The table gives CGs and weights (as % of total body weight W) of segments 1, 2, and 3. Determine coordinates (xCG, yCG) of Centre of Gravity of leg system.

Step 1 - sum of moments of each segment about origin ‘O’ as in Figure 5.39.

MO=xCG{W1+W2+W3}=x1W1+x2W2+ x3W3

xCG = {x1W1 +x2W2 + x3W3}/(W1+W2+W3)

= {17.3(0.106W) + 42.5(0.046W) +

45(0.017W)}/(0.106W + 0.046W + 0.017W)

xCG = 26.9 cm[Oskaya & Nordin, 1991]

O

O

Step 2 - rotate leg to obtain the yCG and repeat the same procedure as Step 1.

MO = yCG{W1 + W2 + W3}

MO = y1W1 + y2W2 + y3W3

yCG = {y1W1 + y2W2 + y3W3}

/(W1 + W2 + W3)

= {51.3(0.106W) + 32.8(0.046W) +

3.3(0.017W)}/(0.106W + 0.046W +

0.017W)

yCG = 41.4 cm

O

C-of-G

Segment Rotational Inertia

Rotational Inertia, I (Mass Moment of Inertia)• real bodies are not point masses; rather the mass is

distributed about an axis or reference point

• resistance to angular motion and acceleration

• depends on mass of body & how far mass is distributed from the axis of rotation

• specific to a given axis

2 ii rmI

Rotational Inertia, I

I = rotational inertiam = massr = distance to axis or point of interest

[Miller & Nelson, 1976]

Rotational inertia can becalculated around anyaxis of interest. Distancefrom axis (r2) has moreeffect than mass (m)

• Radius (k) at which a point mass (m) can be located to have the same rotational inertia (I) as the body (m) of interest

• measures the “average” spread of mass about an axis of rotation; k = “average r”

• not same as C-of-G• k is always a little larger than

the radius of rotation (which is the distance from C-of-G to reference axis)

Radius of Gyration, K

k = I/m

[Hall, 1999]

Example - Radius of Gyration, k

k = I/m

Smaller kSmaller IFaster Spin

Larger kLarger ISlower Spin

Measuring Rotational Inertia, I

Pendulum Method• use frozen cadaver segments• frictionless, free swing, pivot system• measure rotational resistance to swing

I = WL / 2f2

I = rotational inertia (kg.m2)W = segment weight (N)L = distance from C-of-G to pivot axis (m)f = swing frequency (cycles/s)

pivot

C-of-G

fL

[see Lephart, 1984]

Measuring Rotational Inertia, I

Oscillating Beam Method• use live subjects• forced oscillation system• measure resistance to forced rotation

I = R/(2f)2 = Rp2/2

I = rotational inertia (kg.m2)R = spring constant (N.m/rad)p = period (sec)f = freq. of oscillation (cycles/sec)

[Peyton, 1986]

Sources Used• Chaffin et al., Occupational Biomechanics, 1999.• Dempster, Space Requirements of the Seated Operator, 1955.• Hay and Reid, 1988.• Kroemer, “Engineering Anthropometry”, Ergonomics, 32(7):767-

784, 1989• Lephart, “Measuring the Inertial Properties of Cadaver Segments”,

J.Biomechanics, 17(7):537-543, 1984.• LeVeau, Biomechanics of Human Motion, 1977.• Peyton, “Determination of the Moment of Inertia of Limb Segments

by a Simple Method”, J.Biomechanics, 19(5):405-410, 1986.

• Sanders and McCormick, Human Factors in Engineering and Design, 1993.

• Moore and Andrews, Ergonomics for Mechanical Design, MECH 495 Course Notes, Queens Univ., Kingston, Canada, 1997.

• Hall, Basic Biomechanics, 1999.

• Miller and Nelson, Biomechanics of Sport, 1976.

• Kreighbaum & Barthels, Biomechanics: A Qualitative Approach for Studying Human Movement, 1996.

• North, “Ergonomics Methodology”, Ergonomics, 23(8):781-795, 1980.

• Oskaya & Nordin, Fundamentals of Biomechanics, 1991.

• Webb Associates, Anthropometric Source Book, 1978.