Transcript Document
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
Anatomical Frames of Reference
Planes of Motion
Transverse Plane
Frontal Plane
Sagittal Plane
Relative Position
Posterior
Lateral
Lateral
Medial
Medial
Anterior
Top View (Transverse Plane)
A
B
C
A
B
C
Relative Position
Point A is Proximal to point B
Point B is Proximal to point C
Point A is Proximal to point C
Point C is Distal to point B
Point B is Distal to point A
Point C is Distal to point A
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 Dimensions
AGE
Lengths
and
Heights
0 10 20 30 40 50 60 70 80
Age (years)
Static Dimensions
GENDER
[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 Dimensions
PERCENTILE within Specific Population Group
Normal or Gaussian
Data Distribution
No. of
Subjects
5th percentile =
5 % of subjects
have “dimension”
below this value
Dimension
(e.g. height,
weight, etc.)
50 %
95 %
Static Dimensions
HISTORICAL PERIOD
(Europe, US, Canada, Australia)
Increase
in
Average
Adult
Height
(inches)
4 inch increase in 8 decades
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990
Decade
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
Segment Lengths: Link/Hinge Model
• 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
L
Segment
Joint or Hinge
Segment Lengths: Link/Hinge Model
Segment Density
D = M / V = (W/g) / V
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
Segment Density
Double-tank
system for measuring
displaced volume
of human body
segments on living
or cadaver subjects.
Using standardized
density tables, the
mass can then be
calculated using
D = M / V.
[source: Miller & Nelson, 1976]
Segment Center-of-Gravity
Segment
C-of-G
[Kreighbaum & Barthels, 1996]
• 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
Force
30
30
20
distance 9
6
10
3
10
3
20
6
9
C-of-G Line
Force 30
30
20
20
10
Different weight
or mass distributions
can have the same
C-of-G
10
[adapted from
Kreighbaum & Barthels, 1996]
distance 9
6
3
3
6
9
Segment Centers-ofGravity shown as
percentage of segment
lengths [Dempster,
1955].
Segment Center-of-Gravity
Balance Method
• Weight (force of gravity) & vertical reaction force
at the fulcrum (axis) must lie in the same plane.
C-of-G line
[Kreighbaum & Barthels, 1996]
C-of-G line
C-of-G line
Segment Center-of-Gravity
Reaction Board Method 1 – Individual Segments
Sum all moments around
pivot point ‘O’ for both
cases:
-WX – SL – W2L2 = 0
-WX’ – S’L – W2L2 = 0
W2
L2
O
Subtract equations and
rearrange to obtain the
exact location (X) of Cof-G for the shank/foot
system:
X = {L(S - S’)/W + X’}
W2
L2
O
[LeVeau, 1977]
Segment Center-of-Gravity
Reaction Board Method 2 – Group of Segments
Weigh Scales
C-of-G
Support Point
[Hay and Reid, 1988]
Segment Center-of-Gravity
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: SMO = MA + MB + MC = MA+B+C
A
B
30 N
C
5N
10 N
distance
O
2
4
6
8
Multi-Segment Method Example – Leg at 90 deg
O
O
[Oskaya & Nordin, 1991]
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.
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
Step 2 - rotate leg to obtain the yCG and
repeat the same procedure as Step 1.
C-of-G
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 +
O
0.017W)
yCG = 41.4 cm
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
[Miller & Nelson, 1976]
Rotational Inertia, I
I mi ri
2
I = rotational inertia
m = mass
r = distance to axis
or point of interest
Rotational inertia can be
calculated around any
axis of interest. Distance
from axis (r2) has more
effect than mass (m)
Radius of Gyration, K
k = I/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)
[Hall, 1999]
Example - Radius of Gyration, k
Smaller k
Smaller I
Faster Spin
k = I/m
Larger k
Larger I
Slower Spin
Measuring Rotational Inertia, I
Pendulum Method
• use frozen cadaver segments
• frictionless, free swing, pivot system
• measure rotational resistance to swing
pivot
L
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)
f
C-of-G
[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):767784, 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.