Anthropometry Chapter 3 Body Segment Parameters

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Anthropometry(Chapter 3 Body Segment
Parameters)

• Wednesday March 29th
• Dr. Moran

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Lecture Outline

• Review Midterm Exam
• Upcoming Weeks
• Anthropometry Notes

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What is Anthropometry?

• Studies the physical measurements of the human
  body
• Used to study differences between groups
• Race
• Age
• Sex
• Body Type
• Professional Fields ergonomics, automotive,
  etc.
• Mostly care about the inertial properties of the
  body and its segments

Drillis Contini 1966
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Body Segment Parameters

• Length
• Mass
• Location of segemental center of gravity (also
  known as center of mass COM)
• Segmental Mass Moment of Inertia
• Before a kinetic analysis can occur these
  properties must either be measured OR estimated

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Some Important Assumptions

• 1.) Segments behave as RIGID bodies
• Not true as we know that segments are composed of
  bones soft tissues. All of which bend,
  stretch, etc.
• 2.) Some segments over-simplifed
• Ex Foot represented as one segment by many
  researchers

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Assumptions (cont)

• 3.) Segmental mass distribution similar among a
  population
• Allows researches to ESTIMATE an individuals
  segment parameters from the AVERAGE group values
• Important researcher chooses a good match
• For instance, if you wanted to estimate the
  segment parameters for a pediatric subject, then
  you would want to be sure that the average
  segment parameters come for a similar group

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Body Segment Parameters

• 1.) Length
• 2.) Mass
• 3.) Volume
• 4.) Center of Mass
• 4.) Center of Rotation
• 5.) Moment of Inertia

Question How can we determine these BSP values
for a participant in our study?
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DIRECT MEASURE Segment properties are determined
directly from the participant. Only possible
with a cadaver specimen because each
segment would need to be disconnected and
analyzed.
INDIRECT MEASURE Estimation of parameters is
necessary for living participants. There are
numerous techniques to estimate these values
W.T. Dempster Space Requirements of the Seated
Operator US Air Force (1955) Outlined procedures
for DIRECTLY measuring parameters from cadavers
(8) AND included tables for proportionally
determining parameters from cadaver values.
Coefficient Method (Table of Proportions)
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BSP Determination Methods
CADAVER STUDIES
MATHEMATICAL MODELING
SCANNING/IMAGING TECHNIQUES
A laser-aligned method for anthropometry of hands
(Highton et al., 2003)
KINEMATIC
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BSP Parameters

• Segment Length most basic body dimension
• Can be measured from joint to joint
• Dempster et al. (1955, 1959) summarized
  estimates of segment lengths and joint center
  locations relative to anatomical landmarks
• This allows one to ESTIMATE the location of a
  joint by palpating and measuring the easily
  identifiable bony landmarks
• For instance, the hip joint center can be
  approximated from the location of the greater
  trochanter

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Whole Body Density

• Human body comprised of many types of tissues of
  different densities
• Ex cortical bone (specific gravity gt 1.8)
• muscle tissue (just over 1.0)
• fat (lt 1.0)
• Average density is a function of body type
  somatotype

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Average Density (cont)

• Drillis Contini (1966)
• Pondural Index
• c h/w1/3
• w body weight (lbs)
• h height (inches)
• D 0.69 0.0297c kg/l
• Ex Find the whole-body density of Dr. Moran (5
  10 150lbs).

In general (1) the density of distal segments is
gt than proximal segments (2) Individual segments
? as the whole body density ?
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Segment Mass

• Individual Segment Mass is proportional to Whole
  Body Mass
• The total mass of the segment is
• M ? mi
• where mi is the mass of the ith segment
• mi diVi
• Ex A tape measure is used to take thigh
  circumferences every 1 cm. For one measurement
  the circumference is 23.9 cm. Assuming a
  circular cross-section, what is the mass of that
  segment if the average density is 1.059 kg/l.
• circumference 2 p r
• 0.239 2 p r
• r 0.0381
• Volume of Slice (p r2) (thickness)
• V (p 0.03812)(.01) 0.0000456 m3 0.0456
  l
• Mass of Slice (1.059)(0.0456) 0.048 kg
• Simply weigh subject and then multiply by the
  proportion that each segment contributes to the
  total.
• Handout (Table 3.1 from supplemental text)
• Ex What is the mass of the left leg of a person
  that weighs 167 Kg?

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Segmental Center of Mass

• How to determine the center of mass?
• Cadaver Studies find the center of balance point
• Dempster (1955) calculated the COM as the
  distance from the endpoints of the segment
• xcg xproximal Rproximal (xdistal xproximal)
• ycg yproximal Rproximal (ydistal yproximal)
• In Vivo Studies the cross-sectional area and
  length of segment are necessary to approximate
  the segmental COM
• x (1/M) ? mi xi
• Ex From the cross-sectional slice of the thigh
  compute its contribution to the center of mass of
  the thigh if the circumference was taken 12 cm
  from the hip joint.
• mi xi (0.048kg 0.12m)

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Segmental Center of Mass (cont)

• From Table 3.1 calculate the coordinates of the
  center of mass of the foot given the following
  coordinates lateral malleolus (84.9, 11.0), head
  of the 2nd metatarsal (101.1, 1.3).
• xcg 84.9 0.5 (101.1 84.9) 93
• ycg 11.0 0.5 (1.3 11.0) 6.15

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Limb and Total Body COM

• How can you compute the COM of a limb or
  combination of segments?
• First compute the COM of each individual segment
• Use the mass proportional value for that segment
• Use these formulas

? Ps xcg
xlimb
Thus, the heavier a segment the more it affects
the total COM
? Ps
? Ps ycg
ylimb
? Ps
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Reuleauxs MethodUsed for Center of Rotation
Calculation

• Reuleauxs Method (1876)
• Determines the center of rotation for ONE segment
• Can be a 2D, graphical technique

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Mass Moment of Inertia

• Rotational Inertia the resistance of a body to
  change in its rotational motion. The angular or
  rotational equivalent of mass.
• Classically defined as the second moment of
  mass it is the summed distance of mass
  particles from an axis
• Any time a movement involves accelerations we
  need to know the inertial resistance to these
  movements. (F ma M Ia)
• Consider the moment of inertial about the COM, Io
• Io m(?o2)
• where ? the radius of gyration

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Parallel-Axis Theorem

• Most segments do not rotate about their COM, but
  about their joint on either end
• Relationship between moment of inertia about the
  COM and moment of inertia about the joint is
  given by
• I Io mx2

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Moment of Inertia (cont)

• Ex A prosthetic leg has a mass of 3 kg and a COM
  of 20 cm from the knee joint. The radius of
  gyration is 14.1 cm. Calculate I about the knee
  joint.
• Io m(?o2)
• Io 3(0.141)2 0.06 kg m2
• I Io mx2
• I 0.06 3(0.2)2 0.18 kg m2

• Ex Calculate the moment of inertia of the leg
  about its distal end (ankle joint) for an 80 kg
  man with a leg length of 0.435m.
• Mass of Leg 0.0465 x 80 3.72 kg
• Io m(?o2)
• Io 3.72(0.435 x 0.643)2 0.291 kg m2

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A laser-aligned method for anthropometry of hands
(Highton et al., 2003)
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Recent ApplicationMaternal Anthropometry as
Predictors of Low Birth Weight

• Journal of Tropical Pediatrics 52(1)24-29
• Objective The usefulness of maternal
  anthropometric parameters i.e. maternal weight
  (MWt), maternal height (MHt), maternal mid-arm
  circumference (MMAC) and maternal body mass index
  (MBMI) as predictors of low birth weight (LBW)
  was studied in 395 singleton pregnancies. The
  maternal anthropometric parameters were measured
  in the first trimester of pregnancy and were
  plotted against the birth weight of the newborns.
  
• Results Significant positive correlations
  were observed among MWt and birth weight
  (r0.38), MHt and birth weight (r0.25), MMAC and
  birth weight (r0.30) and MBMI and birth weight
  (r0.30). The most sensitive being MWt (t7.796),
  followed by MMAC (t5.759), MHt (t4.706) and
  MBMI (t5.89). For prediction of LBW, the
  critical limits of MWt, MHt, MMAC and MBMI were
  45 kg, 152 cm, 22.5 cm, 20 kg/m2 respectively.

Web Data (Pediatric Anthropometry)
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Muscle Anthropometry

• Prior to calculating muscular forces we need to
  know some muscle measurements
• Physiologic Cross-Sectional Area (PCSA)
• Fiber Length
• Mass
• Pennation Angle
• Important values necessary for computational
  modeling

http//www.duke.edu/bsm/ovlpmris.GIF
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Muscle Cross-Sectional Area

• A measure of the number of sarcomeres in parallel
  with the angle of pull of the muscles.
• Def Sarcomere basic functional unit of a
  myofibril, contains a specialized arrangement of
  actin and myosin filaments necessary to produce
  muscle contraction
• With pennate muscles, the fibers act at an angle
  from the long axis of the fiber
• Because of the off-angle, these muscles do not
  move their tendons as far as parallel muscles do.
  
• Contain more muscle fibers--produce more tension
  than parallel muscles of the same size.

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PCA (cont)

• Non-pennate muscles
• PCA m/(dl) cm
• m mass of muscle fibers, grams
• d density of muscle 1.056 g/cm3
• l length of muscle fibers, cm
• Pennate Muscles
• PCA (m cos T )/(dl) cm
• m mass of muscle fibers, grams
• d density of muscle 1.056 g/cm3
• l length of muscle fibers, cm
• T pennation angle (increases as muscle shortens)

T
T