Anthropometry

1. Anthropometry A.H. Mehrparvar Occupational Medicine Department Yazd University of Medical Sciences

2. Definitions • Anthropology: The science of human beings • Physical anthropology: The study of physical characteristics of human beings • Antropometry: A branch of physical anthropology dealing with body dimensions and measurements.

3. Introduction • the science that deals with the measurement of size, mass, shape, and inertial properties of the human body • the measure of physical human traits to: • determine allowable space and equipment size and shape used for the work • The results are statistical data describing human size, mass and form.

4. Considered Factors: • agility and mobility • Age • Sex • body size • Strength • disabilities

5. Engineering anthropometry: • Application of these data to tools, equipment, workplaces, chairs and other consumer products. • The goal: • to provide a workplace that is efficient, safe and comfortable for the worker

6. Divisions of anthropometry • Static anthropometry –body measurement without motion • Dynamic anthropometry -body measurement with motion • Newtonian anthropometry -body segment measures for use in biomechanical analyses

7. Static Anthropometric Measurements • Static = Fixed or not moving • Between joint centers • Body lengths and contours • Measuring tools: Laser (computer), measuring tape, calipers

8. Dynamic Anthropometric Measurements • Dynamic = Functional or with movement • No exact conversions for static to dynamic • Kromer (1983) offers some rough estimates for converting static to dynamic • e.g. Reduce height (stature, eye, shoulder, hip, etc.) by 3%. • Somatography • e.g. A CAD program named SAMMIE • e.g. A virtual reality program named dv/Maniken • Scale model mock-up

9. Designing for 90 to 95 percent of anthropometric dimensions. • Designing for the “average person” is a serious error and should be avoided • Designing for the tallest individuals (95th percentile): leg room under a table • designing for the shortest individuals (5th percentile): reach capability. • Designing “average person”: Supermarket counters and shopping carts

10. Design Principles • Designing for extreme individuals • Design for the maximum population value when a maximum value must accommodate almost everyone. E.g. Doorways, escape apparatus, ladders, etc. • This value is commonly the 95th percentile male for the target population. • Design for the minimum population value when a minimum value must accommodate almost everyone. E.g. Control panel buttons and the forces to operate them. • This value is commonly the 5th percentile female for the target population.

11. Design Principles, continued • Designing for an Adjustable Range • Designing for the 5th female/95th male of the target population will accommodate 95% of the population. • 95% because of the overlap in female/male body dimensions (if the male/female ratio is 50/50). • Examples are auto seats, stocking hats • Designing for the Average • Use where adjustability is impractical, e.g. auto steering wheel, supermarket check-out counter, etc. • Where the design is non-critical, e.g. door knob, etc.

12. Designing for Motion • Select the major body joints involved • Adjust your measured body dimensions to real world conditions • e.g. relaxed standing/sitting postures, shoes, clothing, hand tool reach, forward bend, etc. • Select appropriate motion ranges in the body joints, e.g. knee angle between 60-105 degrees, or as a motion envelope. • Avoid twisting, forward bending, prolonged static postures, and holding the arms raised

13. 7 Steps to Apply Anthropometric Data • Identify important dimensions, e.g. hip breadth for a chair seat • Identify user population, e.g. children, women, Iran population • Determine principles to use(e.g. extremes, average, adjustable) • Select the range to accommodate, e.g any%, 90%, 95% • Find the relevant data, e.g. from anthropometric data tables. • Make modifications, e.g. adult heavy clothing adds ~4-6 linear inches. • Test critical dimensions with a mock-up, user testing, or a virtual model

14. Variability - three areas • Anthropometric data show considerable variability stemming from the following sources: • Poor data • Interindividual variability • Intraindividual variability

15. Poor data • Variability in measurements arise from: • Population samples • Using measuring instruments • Storing the measured data • Applying statistical treatments

16. Intraindividual variability • Changes in time • Size and body segment size, change with a person’s age -some dimensions increase while others decrease

17. Interindividual variability • Individual people differ in: • arm length • stature and weight • therefore population samples are usually collected from cross sectional studies

18. Long-term trends • Change in body size by time and in different generations

19. Areas of anthropometry • Anthropometry can include just general measurements of dimension of body segments • Lengths • Circumferences (girths) • Breadths (width) • depths • Body composition • In biomechanics, mostly concerned with BSIPs (Body Segment Inertial Parameters) • Segment mass • Center of mass • Moment of inertia

20. Inertial Parameters • Typical biomechanical analyses require the following: • Segment mass • Location of center of mass • Moment of inertia • These properties of a rigid body are often referred to as Inertial Parameters

21. Body Segments • Divide the body into defined rigid bodies, for which we know or can determine the inertial properties • Many different ways to divide the body • Most common (14 segments): • Head • Trunk • Upper arm • Forearm • Hand • Thigh • Shank • Foot

22. Body Segment Model

23. Y (XH,YH) (XK,YK) “Digitizing” (XA,YA) (Xheel, Yheel) (XT,YT) X

24. Rigid Body Analysis • Rigid Body • A body made of particles (points), the distances between which are fixed • What is the basic assumption? • The human body segments are rigid links • Therefore human body can be modeled as a series of rigid bodies (link segments)

25. Air Resistance Body Weight (N) = mg Friction VGRF Rigid Body Model The human body is modeled as a linked system of rigid bodies

26. Free Body Diagram • Diagram of the essential elements of the system • Segments and Axes of interest • Forces acting on the system • Effort and resistance forces • Weights of limbs or segments • Line and point of application for each force • Force Arms (moment arms) • Perpendicular distance from line of force application to axis of rotation • Moment Direction (+/-)

27. Equilibrium and Static Analysis • System is not moving or acceleration is constant • Static Equilibrium • No motion, thus no acceleration • So opposing forces are equal • Rigid Body Diagram • Free Body Diagram • Drawing a mechanical picture of the system or object • Example: Muscle-Lever Diagram

28. Muscle-Lever Diagram • Muscle Diagram • Bones • Muscles • Motion • Lever Diagram • Direction • Force (direction) • Axis • Resistance (direction)

30. Static Analysis • Uses the equations of equilibrium across various postural positions • Allows the determination of: • Maximum or minimum muscle forces or moments for a given posture or joint position and load • Shear or injurious forces across joints in a given positional load or task (e.g. lifting) • How body postures affect joint loads • Resultant joint moments and forces

31. Conditions for Equilibrium Sum of all horizontal forces must be zero Fx = 0 Fy = 0 Sum of all vertical forces must be zero Fz = 0 Sum of all moments about the axis (joint) in each plane must be zero M = 0

32. Free-body Diagram – The System

33. The Free-body Diagram Illustration of the essential elements of a system Upper Arm Segment Forearm Segment

34. i = np i = 1 More Key Terms • Moment of Inertia • The resistance of a body to rotation about a given axis I =Σmi· ri2 • I – moment of inertia about a given axis • np – number of particles making up rigid body • mi – mass of particle • ri – distance between particle and axis

35. Whole Body Center of Mass • Mass – measure of the amount of matter comprising an object (kg) • Center of Mass – location for which mass of a body is evenly distributed • It is the point about which the sum of torques is equal to zero • The point about which objects rotate when in flight • Allows simplification of entire mass particles into a mass acting through a single point

36. Center of Mass

38. n i = 1 3 n i = 1 i = 1 Calculation of Segment Mass m =Σ mi • m is the total mass • mi is the mass of a segment or part • Ex. If we have 3 parts or sections, then m = Σ mi = m1 + m2 + m3 • Mass of segment • mi = ρi·Vi (density times volume) • So… m = ρΣ Vi(assumes uniform density)

39. Multi-segment Systems • x0 = (m1x1 + m2x2 + m3x3) / M • y0 = (m1y1 + m2y2 + m3y3) / M • (x0,y0) is the COM position for the whole

40. Mass Moment of Inertia • M = I·α • M is moment (Nm) • α is the angular acceleration • I is constant of proportionality (inertia) • Resistance to change in angular velocity • Recall: I = m.r2 (r is the moment arm) • I = m1·x12 + m2·x22 + m3·x32 I = Σ mi·xi2 • A mass closer to the axis – Less effect • A mass further from the axis – Greater effect

41. Segment and WBCOM Relation ♀ ~ 55% BH ♂ ~ 56-57% BH

42. Benefits of Understanding COM • Parabolic flight of a projectile • Jump, aerials, hang time • Running performance • Vertical oscillation of COM • Manipulation of COM for greater impulse • Long jump, leap • Mechanical Stability • Base of Support (BOS) • Low COM - STABILITY • High COM - MOBILITY

43. Stability • Factors that influence stability • Base of Support • Center of Mass Location • Mass

44. Whole Body Center of Mass • Computation of whole body COM • Where: • CMWB x or y : Location of whole body COM in x or y plane • MWB : Mass of whole body • Mi : Mass of ith segment • CM xi or yi : Location of COM of ith segment in x or y direction

45. Whole Body Center of Mass • For analysis…the person is often divided into many parts (each considered a rigid body) • We may want to know the center of mass of the entire system • Need: • Masses of each of the segments • Locations of the centers of mass of each segment • Whole body center of mass position is equivalent to a weighted mean of all the parts

46. Whole Body Moment of Inertia • May have moments of inertia of segments • From tables or whatever • Want moment of inertia of the whole body about it’s COM • Useful when analyzing aerials (flight) • What we need: • Masses of the segments • Locations of segment COM • Location of whole body (system) COM • Moments of inertia of each segment about the whole body COM • The moments of inertia can be summed once they are all about the same axis

47. Problem • So…how do we determine inertial parameters of limb segments in a live subject? • Answer: Amputate

48. Determination of COM Position • So, since we can’t just lop off peoples limbs… • Typically use tables and regression equations from previous studies: • Dempster, 1955 • Clauser et al., 1969 • Chandler et al., 1975 • Vaughan et al., 1992

49. Measures • Mostly simple measures do the trick • Some are more complicated if the measures serve as a guide for man-machine interface requiring a person to perform a task • Kinetics and kinematics are typically needed • Get an idea of ROM, height requirements etc. • Masses, moments of inertia and their locations

50. Locating the COM of a Body Segment • In case you can’t get permission to amputate… • Early Methods: • Suspension • Segmentation (uses tables of regression equations) • Reaction (balance) Board Advantages and disadvantages for each?