Chap 3 Anthropometry

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Chap 3 Anthropometry
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3.0 Scope of Anthropometry in Movement
Biomechanics

• Anthropometry ?
• The major branch of anthropology
• Physical measurements of the human body to
  determine differences in individuals and groups
• Human movement analysis requires kinetic measures
  (mass, moment of inertia, and their locations)
• Joint centers of rotation, the origin and
  insertion of muscles, the angles of pull of
  tendons, and the length and cross-sectional area
  of muscles are also required.

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3.0 Scope of Anthropometry in Movement
Biomechanics

• Segment Dimensions
• The most basic body dimension is the length of
  segments between each joint
• estimates of segment lengths and joint center
  locations relative to anatomical landmarks
  Dempster(1955,1959)
• Drillis and Contini(1966) an average set of
  segment lengths expressed as a percentage of body
  height (p52, Fig 3.1)

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3.1 Density, Mass, and Inertial Properties

• Measured from cadavers or segment volumes and
  density table
• Whole-Body Density
• Drillis and Contini(1966) using a function
  of ponderal index ch/w1/3
• 
  d 0.690.0297C kg/l (pound-inch)
• d 0.690.9C
  kg/l (metric unit)
• A short fat person has a lower PI than a tall
  skinny person
• ? lower body density

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3.1 Density, Mass, and Inertial Properties
Ex 3.1) Using Eq (3.1) and (3,2), calculate the
whole-body density of an adult whose height is
510 and who weighs 170lb.
from Eq (3.1),
In metric unit,
from Eq (3,2),
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3.1 Density, Mass, and Inertial Properties

• Segment Densities
• Segment density is not uniform.
• Density of distal segment is greater than
  proximal segments.
• because of the higher proportion of bone (p
  54. Fig 3.2)

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3.1 Density, Mass, and Inertial Properties
Segment Mass and Center of Mass

• CoG CoM in the direction of gravity only
• Total body mass increases, as segment mass
  increases.
• Segment mass can be expressed as a percentage of
  the total mass.
• (p56, Table 3.1)
• Cadaver by determining the center of balance of
  each segment
• In vivo the profile of cross-sectional area and
  length

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3.1 Density, Mass, and Inertial Properties
- total mass M
where mi is the mass of the i th section
di density of i th section, Vivolume of i th
section
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3.1 Density, Mass, and Inertial Properties
If d is uniform,
Consider the CoM to be located a distance x from
the left edge of the segment
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3.1 Density, Mass, and Inertial Properties
Ex 3.2) From anthropometric data in Table 3.1,
calculate the coordinates of the COM of the foot
and the thigh given the following conditions.
Ankle(84.9, 11.0), metartasal(101.1, 1.3),
greater trochanter(72.1, 92.8), lateral femoral
condyle(86.4, 54.9).
For the foot from the Table 3.1, foot COM is at
the center of the distance between the lateral
malleolus(ankle) and the MT markers
For the thigh from the Table 3.1, thigh COM is
0.433 from the proximal end of the segment.
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3.1 Density, Mass, and Inertial Properties

• Center of Mass of a Multi-segment System

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3.1 Density, Mass, and Inertial Properties

• Mass Moment of Inertia and Radius of Gyration

In the rotational sense
M the moment of force causing the angular
acceleration a I Depend on the point about
which the rotation is taking place Imin at
the CoM
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3.1 Density, Mass, and Inertial Properties

• Mass Moment of Inertia and Radius of Gyration

the moment of inertia about the left end
Consider the moment of inertia Io about the CoM
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3.1 Density, Mass, and Inertial Properties
Parallel-Axis Theorem
Two equal masses same moment of inertia in the
plane of rotation about the
center
of mass as original distributed segment
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3.1 Density, Mass, and Inertial Properties
Ex 3.3) (a) A prosthetic leg Mass3kg, COM20cm
from the knee joint Radius of
gyration14.1cm Calculate I about the knee
joint.
(b) If the distance between the knee and the hip
joints is 42cm, calculate Ih for this prosthesis
about the hip joint as the amputee swings through
with a locked knee.
Note that 20 times of
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3.1 Density, Mass, and Inertial Properties

• Use of Anthropometric Table and Kinematic Data
  

Calculation of Segment Masses and Centers of Mass
Ex 3.4) Calculate the mass of the foot, shank,
thigh and HAT and its location from the proximal
or distal end. body mass of the subject 80kg
direct measure segment lengths
foot0.195m, leg0.435m, thigh 0.410m ,
HAT 0.295m
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3.1 Density, Mass, and Inertial Properties
Calculation of Total-Body Center of Mass
for an n-segment body system the center of mass
in the X direction
for the fraction of total body mass
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3.1 Density, Mass, and Inertial Properties
Calculation of Total-Body Center of Mass
Ex 3.5) Calculate the total-body COM ay a given
frame 15. The time for one stride was 68 frames.
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3.1 Density, Mass, and Inertial Properties
Calculation of Moment of Inertia
Ex 3.6) Calculate the moment of Inertia of the
leg about its CoM, distal end, and proximal end.
From Table 3.1, mass of the leg0.0465X803.72kg
Leg length0.435m Radius of gyration/segment
length0.302 for COM 0.528 for the proximal
end 0.643 for the distal end
for the COM,
for the proximal end,
for the distal end,
Using parallel-axis theorem,
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3.1 Density, Mass, and Inertial Properties
Calculation of Moment of Inertia
Ex 3.7) Calculate the moment of Inertia of HAT
about its proximal end and about its COM.
From Table 3.1, mass of HAT0.678X8054.24kg H
AT length0.295m Radius of gyration/segment
length1.456 for the proximal end 0.903 for
the COM COM/segment length1.142 from the
proximal end
for the proximal end,
for the COM,
or
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3.2 Direct Experimental Measures
Location of the Anatomical Body CoM
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3.2 Direct Experimental Measures
Calculation of the CoM of a Distal Segment
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3.2 Direct Experimental Measures
Moment of Inertia of a Distal Segment
Quick-Release method can be used to calculate I
directly assuming the proximal segment
is fixed
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3.2 Direct Experimental Measures
Joint Axes of Rotation
an instantaneous tangential velocity
in Cartesian coordinates
Therefore,
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3.3 Muscle Anthropometry
Cross-Section Area of Muscles

• The functional cross-sectional areas (PCA) of
  muscle is measure of the number of sarcomeres in
  parallel with the angle of pull of the muscles.
• In parallel-fibered muscle the PCA,

mass of muscle fibers, g density of muscle,
g/cm2 length of muscle fibers, cm

• In pennate muscles, the physiological
  cross-sectional area becomes

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3.3 Muscle Anthropometry
Change in Muscle Length during Movement
-Grieve and colleagues(1978) a study on 8
cadavers reported percentage
length change of the gastrocnemius
muscle as a function of the knee and ankle
angle Force per Unit Cross-sectional
Ares(Stress) - a wide range of stress
values for skeletal muscles - during
isometric conditions range from 20to 100N/m2
- higher values were reported in pennate
muscles because cross-section area
increase
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3.3 Muscle Anthropometry
Mechanical Advantage of Muscle - muscle
unique moment arm length - moment arm
length a line normal to the muscle
passing through the joint center
change with the joint angle -Smidt (1973)
Multi-joint Muscles - most muscles pass
over more than one joint. - these muscle
length may be short to allow a complete range of
movement of both joint involved -
Elftman(1966)