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Anthropometrics
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Top View (Transverse Plane)
Anterior
Posterior
Lateral Lateral
Medial Medial
Relative Position
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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
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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
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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
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Static
Dimensions
[Source: Kroemer, 1989]
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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)
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Static Dimensions
AGE
Age (years)
0 10 20 30 40 50 60 70 80
Lengths
and
Heights
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Static Dimensions
GENDER
[Sanders &
McCormick]
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Static Dimensions
ETHNICITY
[Sanders &
McCormick]
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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.)
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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
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Dynamic (Functional) Dimensions
[Source: North, 1980] 16
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Measurement of
AnthropometricDimensions
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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
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Segment Lengths: Link/Hinge Model
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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
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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]
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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
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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
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Segment Centers-of-
Gravity shown aspercentage of segment
lengths [Dempster,
1955].
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Balance Method
Weight (force of gravity) & vertical reaction force atthe 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 line25
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Reaction Board Method 1Individual Segments
Segment Center-of-Gravity
[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
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Reaction Board Method 2 Group of Segments
[Hay and Reid, 1988]
Segment Center-of-Gravity
Weigh Scales
Support Point
C-of-G
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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
Segment Center-of-Gravity
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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
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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
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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
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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)
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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]
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Example - Radius of Gyration, k
k = I /m
Smaller k
Smaller I
Faster Spin
Larger k
Larger I
Slower Spin
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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]
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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]
Recommended