Cornell University Ergonomics Web
DEA3250/6510 CLASS NOTES
Anthropometrics and Design
1. Design Limitations
a. Myth of designing for the "average" person - since there are no people whose body dimensions are all at the 50th percentile. Body dimensions aren't linearly correlated so people with short arms don't necessarily have short legs, etc. While the use of the 5th and 95th percentiles on one body dimension may exclude 10% of the population, the use of these on 13 dimensions actually can exclude 52% of the population.
b. Myth that designing for 5-95th percentile - designing to include the ranges between the 5th and 95th percentiles of anthropometric data doesn't fit everyone. There are two misunderstandings:
(1) 5 - 95 percentile is only 90% - 5-95% _ 95% of people, it's only 90%! If you design for 90%, you'll fit 9 out of 10, 90 out of 100, 900 out of 1000, etc.
(2) Anthropometrics are based on population "norms" - must consider differences if dealing with a subpopulation such as a group of Southeast Asians or offices for a pro basketball team.
c. Use appropriate anthropometric data- anthropometric data are only specific to the populations which they describe. If the population is poorly specified the percentiles may be biased. Also, percentiles are only specific to the dimension which they describe.
(1) Maximum value - Examples include door clearances and door widths for wheelchairs and users (arms must work the chair), getting a gurney through a door, and railings.
(2) Minimum clearances - Examples include safety clearances for railings and elevator buttons.
d. Design for an adjustable range - but beware of the cost/benefits of including more percentiles. Each successive percent of the population to be accommodated increases the costs relative to the benefits, i.e. there are no diminishing returns.
2. Design Aids -
a. Data tables - have anthropometric data but may be difficult to find and use.
b. Humanscale - a series of templates are used by a computer to change relevant attributes as populations change. Values are printed. Unfortunately, it's still necessary to draw the figures from the data values.
c. Mannequins - a two-dimensional drawing or figure which articulates like ADAM (Anthropometric Data Applications Mannequin) with plastic parts snap together like clear moveable paper dolls or overlay transparencies.
d. Models - three-dimensional models like "George" can be useful as examples of anthropometric data. Models have often been used by clothing manufacturers.
e. Computer generated models - three-dimensional models of a user at a specified percentile in certain respects. Can see elevation, plan, or perspective. An example is "SAMMIE", System for Aiding Man-Machine Interaction and Evaluation. Image can be changed to simulate motion but we don't have good data for most biomechanics.
3. Issues of diversity - a wide variety of factors influence human body dimensions, including the following categories. "Clinical normality" in height is defined as about the range 54"-79". The average stature worldwide is 64.96" ´ 3.15" for men and 60.5" ´ 2.95" for women.
a. Ethnic differences - shortest people in the world are the Efe & Basua "pygmies" in Africa. There men are 56.61" ´ 2.79" for men and 54.01 ´ 3.07"for women. The largest are in southern Sudan, are the Dinka Nilotles with men at 72" ´ 2.4" and women at 66.49" ´ 2.28". The smallest living person is 29 1/2", a male Portuguese professional drummer. The smallest person ever recorded was a Dutch woman at 23.2" tall (1876-1895). The tallest living person is a Pakistani male at 94.09" tall. The tallest ever recorded was an American man at 107 1/2" tall (1918-1940). (He had to eat ~ 8000 calories per day).
(1) Sitting height - Stature differences become reduced when sitting down.
Sitting height - relative sitting height = sitting height ~ 53%
Different ethnic groups have different physical characteristics. Black Africans have proportionally longer legs than Europeans. Eastern people (Asians) have proportionally shorter lower limbs. This is most pronounced for Japanese and less so for Chinese, Koreans, Thai's, and Vietnamese. However, there is some evidence that this situation is changing and that Japanese youth have proportionally longer legs and wider faces.
(2) General rules - Two general rules have been developed which apply to ethnic differences.
(a) Bergman's rule - the body size of varieties increases with decreasing mean temperature of the habitat. Example: the ideal shape to be in the Arctic is a sphere.
(b) Allen's rule - the relative size of exposed portions of the body decreases with decreasing temperature, i.e. nose, ears, toes, extremities will be proportionately smaller.
b. Body shape - soft tissue varies in shape and these variances may create differences in clearance and mobility requirements.
1) mesomorph - body shape larger in the middle.
2) ectomorph - very slender.
3) endomorph - overweight or pregnant with a wider body overall.
c. Sex differences - have important ergonomic consequences and separate data is usually used for men and women.
(1) Dimensions - Men exceed women in all linear body dimensions except hip breadth. The lengths of upper and lower limbs are absolutely and proportionally greater in men than women except for buttock-knee length. Women exceed men for skinfold thickness.
(2) Soft tissue distribution - generally, fat is a greater proportion of body weight in women than men. Women have an increase in subcutaneous fat in breasts, hips, thighs, and upper arms. Abdominal fat tends to accumulate below the navel in women and above the navel in men.
d. Growth and development - rates are very fast for children but decline with age.
(1) Children - At birth, average weight is 7.26lb ´ .88lb and average height is 19.7in ´ .8in. Trunk is 70% of body length at birth but only 52% of adult stature. Girls reach 50% of adult height before 2 years of age. Boys do the same at around 2 years of age. From birth to 20 years of age the body length increases 3-4 times and weight increases 20 times.
(2) Adolescents - Associated with puberty, boys begin a growth spurt from around 11.5 years of age which lasts until around 14 years of age. Girls spurt starts earlier, at around 9 years of age. It reaches its maximum rate around 12 years old and is completed by around 16 years of age. At the same time height is changing, relative body proportions are as well.
e. Age group - It's important to consider whether children or elderly people are included in anthropometric data.
(1) Height - Average heights of adults in the UK and US steadily decline with age after 20 years of age. Around 40 years of age most people begin to shrink in stature. Women shrink more than men and shrinkage accelerates with age.
This shrinkage occurs in the intervertebral discs of the spine, possibly causing rounding of the back. Some reduction in height may result from shrinkage of lower limbs around the joints.
(2) Weight - The average weight of adults increases from ages 20-45. From age 50 onward men's weight declines. From age 60 onward women's weight declines. Until 55 years of age weight increases for heights and there is an increase in hip breadth. Fat is redistributed from subcutaneous areas to deeper positions especially around abdominal organs. Lean body weight decreases with age as muscles waste away. There is a decrease in muscular strength but the mechanical tensile breaking strength of bone, muscle, and connective tissue decreases with age.
f. Disabilities - Worldwide, an estimated 400 million people cope with physical disability. In the US in 1970 69 million citizens had some physical disability. 5.4 million were visual problems, 20.1 million auditory problems, 18.3 million arthritis, and 7 million with mobility problems (.5 million wheelchair users). There is very limited anthropometric data.
(1) Wheelchair Users - Chairbound people actually suffer three limitations:
(a) Condition which necessitates wheelchair use.
(b) Lower eye-level - eye-level is 15 to 16 inches below that of most standing people and the seated posture also influences reach, controls, and access.
(c) Possession of a cumbersome, awkward, space-consuming, distinctive and inelegant vehicle. While a standing person occupies 25in by 15in of floor space, requires 16in to 26in aisle width and can turn on the spot, a wheelchair user occupies up to 57in by 25in of floorspace, requires minimum aisle clearance of 31.5in and needs a turning circle of between 59in and 67in.
g. Pregnancy - Later stages of pregnancy decreases in the ability to lift, bend, reach, stand or walk for long periods, turn head, etc. so it is a form of temporary disability. Assuming a 0.02% pregnancy rate and 50,000,000 women of childbearing age, means an estimated 1,000,000 pregnant women at any time. Only recently have anthropometric surveys of pregnant women begun to be conducted (in Japan).
h. Time of day - Because the cartilaginous discs of the spinal column get compressed by body weight throughout the day we tend to be slightly shorter in the evening. Additionally, extremities (like feet) swell throughout the day, making them puffier in the evening.
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