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

Top View (Transverse Plane) Relative Position Posterior Lateral Lateral Medial Medial Anterior Top View (Transverse Plane)

Relative Position Point A is Proximal to point 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 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 50 % 95 % Dimension (e.g. height, weight, etc.)

(Europe, US, Canada, Australia) Static Dimensions HISTORICAL PERIOD (Europe, US, Canada, Australia) Decade 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 Increase in Average Adult Height (inches) 4 inch increase in 8 decades

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 Joint or Hinge Segment

Segment Lengths: Link/Hinge Model

D = M / V = (W/g) / V 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

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 [Kreighbaum & Barthels, 1996] Segment C-of-G 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 Different weight or mass distributions distance 9 6 3 distance Force 30 20 10 Different weight or mass distributions can have the same C-of-G C-of-G Line 30 20 10 9 6 3 Force distance [adapted from Kreighbaum & Barthels, 1996]

Segment Centers-of-Gravity 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]

Segment Center-of-Gravity Reaction Board Method 1 – Individual Segments O W2 L2 Sum all moments around pivot point ‘O’ for both cases: -WX – SL – W2L2 = 0 -WX’ – S’L – 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’} [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 O 4 6 8 2 30 N 10 N 5 N A B C distance

Multi-Segment Method Example – Leg at 90 deg 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 O O [Oskaya & Nordin, 1991]

Step 2 - rotate leg to obtain the yCG and 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

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

Rotational Inertia, I I = rotational inertia m = mass [Miller & Nelson, 1976] Rotational Inertia, I 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)

k = I/m Radius of Gyration, K 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]

k = I/m Example - Radius of Gyration, k Smaller k Smaller I Faster Spin k = I/m Larger k Larger I Slower Spin

I = WL / 2f2 L f Measuring Rotational Inertia, I Pendulum Method use frozen cadaver segments frictionless, free swing, pivot system measure rotational resistance to swing pivot C-of-G f 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) [see Lephart, 1984]

Measuring Rotational Inertia, I [Peyton, 1986] Oscillating Beam Method use live subjects forced oscillation system measure resistance to forced rotation I = R/(2f)2 = Rp2/2 I = rotational inertia (kg.m2) R = spring constant (N.m/rad) p = period (sec) f = freq. of oscillation (cycles/sec)

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):767-784, 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.