Anthropometry (Chapter 3 – Body Segment Parameters) Wednesday March 29 th Dr. Moran.

Anthropometry(Chapter 3 – Body Segment Parameters)

Wednesday March 29th

Dr. Moran

Lecture Outline

• Review Midterm Exam

• Upcoming Weeks

• Anthropometry Notes

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

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

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

Assumptions (con’t)

3.) Segmental mass distribution similar among a population

Allows researches to ESTIMATE an individual’s 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

Body Segment Parameters

1.) Length2.) 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?

DIRECT MEASURE

Segment properties are determined directly from the participant. Only possible with

a cadaver specimen because each segmentwould need to be disconnected and

analyzed.

INDIRECT MEASURE

Estimation of parameters is necessary for living participants. There are numerous

techniques to estimate these values

Coefficient Method (Table of Proportions)

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.

BSP Determination Methods

CADAVER STUDIES

MATHEMATICALMODELING

SCANNING/IMAGINGTECHNIQUES

KINEMATIC

A laser-aligned method for anthropometry of hands (Highton et al., 2003)

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

Whole Body Density

• Human body comprised of many types of tissues of different densities

• Ex: cortical bone (specific gravity > 1.8)

muscle tissue (just over 1.0)

fat (< 1.0)

• Average density is a function of body type: somatotype

Average Density (con’t)

• 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 > than proximal segments

(2) Individual segments ↑ as the whole body density ↑

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 segmentmi = 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 π r 0.239 = 2 π rr = 0.0381Volume of Slice = (π r2) (thickness)V = (π * 0.03812)(.01) = 0.0000456 m3 =

0.0456 lMass 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?

m = (0.0465) * (167)m = 7.7655 Kg

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)

Segmental Center of Mass (con’t)

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

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:

xlimb =∑ Ps xcg

∑ Ps

ylimb =∑ Ps ycg

∑ Ps

Thus, the heavier a segment the more it affects the total COM

Reuleaux’s MethodUsed for Center of Rotation Calculation

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

A1

B1

A2

B2

Center of Rotation

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 = Iα)

• Consider the moment of inertial about the COM, Io

Io = m(ρo2)

where ρ = the radius of gyration

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

Moment of Inertia (con’t)• 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(ρo2)

• 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(ρo

2)

• Io = 3.72(0.435 x 0.643)2 = 0.291 kg ∙ m2

A laser-aligned method for anthropometry of hands

(Highton et al., 2003)

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 (r=0.38), MHt and birth weight (r=0.25), MMAC and birth weight (r=0.30) and MBMI and birth weight (r=0.30). The most sensitive being MWt (t=7.796), followed by MMAC (t=5.759), MHt (t=4.706) and MBMI (t=5.89). 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)

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

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.

PCA (con’t)

• 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 Θ )/(dl) cm

» m = mass of muscle fibers, grams» d = density of muscle = 1.056 g/cm3

» l = length of muscle fibers, cm» Θ = pennation angle (increases as muscle

shortens)

ΘΘ