l2 - 321anthropometrics_lec2

8/9/2019 L2 - 321Anthropometrics_Lec2

1/37

Anthropometrics

1


2/37


3/37

Top View (Transverse Plane)

Anterior

Posterior

Lateral Lateral

Medial Medial

Relative Position

3


4/37

A

B

C

A

B

C Point A is Proximalto point B

Point B is Proximalto point C

Point A is Proximalto point C

Point C is Distalto point B

Point B is Distalto point APoint C is Distalto point A

Relative Position

4


5/37

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

5


6/37

Static Dimensions

Definition:Measurements taken when thehuman body is in a fixed position, which typicallyinvolves 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

6


7/37

Static

Dimensions

[Source: Kroemer, 1989]

7


8/37

Static Dimensions

Static Dimensions are related to and vary with otherfactors, such as

Age

Gender

Ethnicity

Occupation

Percentile within Specific Population Group Historical Period (diet and living conditions)

8


9/37

Static Dimensions

AGE

Age (years)

0 10 20 30 40 50 60 70 80

Lengths

and

Heights

9


10/37

Static Dimensions

GENDER

[Sanders &

McCormick]

10


11/37

Static Dimensions

ETHNICITY

[Sanders &

McCormick]

11


12/37


13/37

Static Dimensions

PERCENTILE within Specific Population Group

Normal or Gaussian

Data Distribution

No. ofSubjects

5th percentile =

5 % of subjects

have dimension

below this value

50 %

95 %

Dimension

(e.g. height,

weight, etc.)

13


14/37


15/37

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 DynamicSituations 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 thevalue of a measurement parameter e.g. Arm Reach = arm length + shoulder movement +

partial trunk rotation and + some back bending + handmovement

15


16/37

Dynamic (Functional) Dimensions

[Source: North, 1980] 16


17/37

Measurement of

AnthropometricDimensions

17


18/37

Segments are modeled as rigid mechanical links ofknown physical shape, size, and weight.

Joints are modeled as single-pivot hinges.

Standard points of reference on human body aredefined in the scientific literature and are notarbitrarily used in ergonomics

Less than 5% error by this approximation

Segment Lengths: Link/Hinge Model

L

Joint or Hinge

Segment

18


19/37

Segment Lengths: Link/Hinge Model

19


20/37

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

20


21/37

Segment Density

Double-tanksystem for measuring

displaced volume

of human body

segments on living

or cadaver subjects.

Using standardized

density tables, the

mass can then be

calculated usingD = M / V.

[source: Miller & Nelson, 1976]

21


22/37

Important to know the location of theeffective center of gravity (or mass)

of segments

Gravity actually pulls on every

particle of mass, therefore givingeach part weight

For the body, each segment is treated

as the smallest division of the body

Can obtain C-of-G for individualsegments 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

22


23/37

9 6 3963

distance

Force30

20

10

30

20

10

[adapted from

Kreighbaum & Barthels, 1996]

C-of-G Line

30

2010

30

2010

9 6 3 963

Force

distance

Different weight

or mass distributionscan have the same

C-of-G

23


24/37

Segment Centers-of-

Gravity shown aspercentage of segment

lengths [Dempster,

1955].

24


25/37

Balance Method

Weight (force of gravity) & vertical reaction force atthe fulcrum (axis) must lie in the same plane.

[Kreighbaum & Barthels, 1996]


C-of-G line

C-of-G line

C-of-G line25


26/37

Reaction Board Method 1Individual Segments


[LeVeau, 1977]

Sum all moments around

pivot point O for both

cases:

-WXSLW2L2= 0

-WX SL 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

26


27/37

Reaction Board Method 2 Group of Segments

[Hay and Reid, 1988]


Weigh Scales

Support Point

C-of-G

27


28/37


29/37

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: SMO= MA+ MB+ MC= MA+B+C

O 4 6 82

30 N 10 N 5 N

A B C

distance


29


30/37

Multi-Segment Method ExampleLeg at 90 deg

A leg of is fixed at 90 degrees. The table

gives CGs and weights (as % of totalbody weight W) of segments 1, 2, and 3.Determine coordinates (xCG, yCG) ofCentre of Gravity of leg system.

Step 1- sum of moments of each segmentabout origin O as in Figure 5.39.

SMO=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

30


31/37

Step 2- rotate leg to obtain the yCGand

repeat the same procedure as Step 1.

SMO= yCG{W1 + W2 + W3}

SMO= 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

31


32/37

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 distributedfrom the axis of rotation

specific to a given axis

32


33/37

2

ii rmI

Rotational Inertia, I

I = rotational inertia

m= mass

r= distance to axis

or point of interest

[Miller & Nelson, 1976]

Rotational inertia can be

calculated around any

axis of interest. Distance

from axis (r2) has moreeffect than mass (m)

33


34/37

Radius (k) at which a pointmass (m) can be located to

have the same rotationalinertia (I) as the body (m) ofinterest

measures the average spreadof mass about an axis ofrotation; k= average r

notsame as C-of-G kis always a little larger than

the radius of rotation (whichis the distance from C-of-G toreference axis)

Radius of Gyration, K

k = I /m

[Hall, 1999]

34


35/37

Example - Radius of Gyration, k

k = I /m

Smaller k

Smaller I

Faster Spin

Larger k

Larger I

Slower Spin

35


36/37

Measuring Rotational Inertia, I

Pendulum Methoduse 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 topivot axis (m)

f = swing frequency (cycles/s)

pivot

C-of-G

f

L

[see Lephart, 1984]

36


37/37

Measuring Rotational Inertia, I

Oscillating Beam Methoduse 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]

l2 - 321anthropometrics_lec2

Documents