AY2122 Module 3 Ergonomics - INEN 30133 PDF

# MODULE 3 - ANTHROPOMETRY ## Course Objectives - Learn about Anthropometry and the measurement of the human body - Describe body sizes of and other associated characteristics for designing devices - Learn how anthropometric data helps in the design of workstations and facilities ## Overview The...

# MODULE 3 - ANTHROPOMETRY ## Course Objectives - Learn about Anthropometry and the measurement of the human body - Describe body sizes of and other associated characteristics for designing devices - Learn how anthropometric data helps in the design of workstations and facilities ## Overview The word "anthropometry" is derived from the Greek words "Anthropos" (man) and "Metron" (measure) and means measurement of the human body. Anthropometric data are used in Human Factors Engineering (HFE) to specify the physical dimensions of workspaces, equipment, vehicles, and clothing to ensure that these products physically fit the target population and make sure that physical dimensions of workspaces would fit the employees. ## Course Materials ### ANTHROPOMETRY The study of body sizes and other associated characteristics is generally referred to as anthropometry. While the term typically refers to static space dimensions, such as length, width, and shape, other important anthropometric measurements include the weights and inertial properties of body parts. Anthropometric measurements are essential when designing devices and/or systems to fit the users or employees. For example, almost everyone would expect doors in buildings to be well above 6 feet (1.83 m) tall, because we are well aware that many people exceed 6 feet in height. But how large should the diameter of a screwdriver handle be, if you want the human hand, including fingers and the thumb, to surround the circumference? Or suppose that you are designing eye-glasses and you want the hinges outboard of the glass frames to be slightly smaller than the width of the human head just above the ears. What size do you need? Clearly, people who design products for the human body need to know something about the wide variety of body sizes which are possible, and that is what this module is about. Much of the collected anthropometric data has been taken from selected subpopulations, rather than the population as a whole, partly because many studies were originally directed at some specific design question asked by clothing or footwear manufacturers. A great deal of the data was obtained for the military to help determine the sizes of uniforms and properly design equipment. A historical note is that anthropometrists originally used tape measures and other devices to make direct measurements of people. Since that process was very time consuming, it was largely dropped in favor of working extensively with photographic records. The use of photographs for measurement also improved the repeatability of measurements because all measurements were made on a flat surface. More recently, the use of laser scanning devices, interfaced with computer data collection software, has greatly reduced the time needed to collect information on body shapes. This potentially revolutionary development is already leading to new applications of anthropometric data. ## Types of Anthropometric Data Used in Ergonomics 1. **Structural data:** Measurements of bodily dimensions of subjects in static postures. Anatomically rigorous, in that measurements are made from clearly identifiable sites, usually bony landmarks under the skin. Typically used to optimize furniture, clothing, and vehicle cab dimensions. 2. **Functional data:** Collected from subjects who are allowed to move one or more limbs in one or more planes with respect to a fixed point. The shape of the 3D surface swept by moving the arm with the elbows extended or the amount of forward reach when the subject can bend at the hip. Takes into account the fact that in natural movements, several joints are involved and generates workspace "envelopes" whose size increases with the number of joints allowed to move. 3. **Newtonian data:** This included both body segment mass data and data about the forces that can be exerted in different tasks. ## Sources of Human Variability Humans vary due to genetic differences (in inherited characteristics); plasticity (the capability of being molded by the environment when young); acclimatization; and over the very short term, behavioral adaptation. Only the last two of these forms of adaptation are reversible. Roberts (1995) cites evidence of plasticity in a population where the heads of people who were habitually placed in a supine position in the first years of life grew to be broader than those that were more often placed on their sides. Boas (1910) found that children born to immigrant parents after arrival in the United States were larger and had different shaped heads to those born before the parents migrated. This challenged prevailing views about the fixity of racial or ethnic "types." Children born in Canada of Punjabi parents are taller and weigh more than those born in India (Bogin, 1995). One major complicating issue is that anthropometric measurements show consistent variation between members of different ethnic groups, between genders, and over time. NASA and other organizations have attempted to document ethnic and other differences in stature data. Much of the information they have assembled shows that human stature has been increasing worldwide since the mid-1800s. The average heights of military personnel worldwide have shown dramatic increases from about 1,715 mm during the early part of this century to 1,775 mm (or slightly more) in 1980. That increase represents a rate of growth in the human stature of about 1 mm a year. Although the accuracy of some of the older records may be debatable, nearly all countries with records going back very far have shown a continual upward trend in stature. Many people attribute this worldwide change to better diets. Those data also tend to show ethnic differences. For example, Norwegian and Danish statures have tended to be the greatest of many reported in the world. Among Europeans, the stature of the French tends to be the smallest historically. The stature of the Japanese tends to be very much smaller than those of European nationalities during the early part of the 20th century, but this is changing quickly. An interesting note is that since the 1980s, the number of females in the U.S. military has increased significantly. Consequently, the rate of increase in the mean height of U.S. military personnel has been slowed. ## Factors Influencing the Change in Body Size of Populations Better living conditions are associated with larger body size. Smallness does not appear to be intrinsic to many groups of people, but it is related to development in a biologically stressful environment, a plastic response to deprivation. Many industrialized countries have witnessed an increase in population size over the last 150 years. This in, part, due to better diet, better sanitation, childhood immunization, refrigerated transportation making available a year-round supply of fresh food, and supplementation of dairy products and cereals with vitamin D. In the United States, Britain, and parts of Northern Europe, this trend seems to have slowed among children of indigenous families (Cole, 2000; McCook, 2001). According to the U.S. Center for Disease Control and Prevention the mean stature of U.S. males and females (175.25 and 162.56 cm, respectively) has not changed since the 1960s; therefore, data from that era are still usable for ergonomic purposes. In the United Kingdom, however, mean male stature increased by 1.7 cm between 1981 and 1995 and mean female stature increased by 12 mm (Peebles and Norris, 1998). With industrialization came scattering of previously isolated rural communities, resulting in outbreeding or heterosis, which is thought to result in a genetically healthier population. Boldsen (1995) investigated the secular trend in stature of Danish males over the last 140 years. He found an increase of 13 cm in mean male stature over this time, 45% of which was due to a change in the population structure, that is, due to heterosis, and the rest a plastic response to improved living conditions. Since the body sizes are related to height, it is interesting to note that height changes with age. Children grow and older people shrink. But child growth differs between the genders. Note that at younger ages, females grow a bit faster than males, but males grow more overall. ## Predicting the Segment Mass of the Human Body Human physical activities normally involve movement. The larger the mass of the body part that is moved, the greater the forces needed to move it. For this and other reasons it is often useful to be able to predict the mass of different segments of the body. Some of the work at NASA provides an empirical basis for predicting those mass magnitudes. They made traditional body mass measurements and then ran statistical regression analyses in which they predicted the weight of the specific body segments as a function of the person's overall body weight (W). Examples include a general tendency for older people to weigh more, for taller people to be heavier, for heavier people to have larger waists, etc. More importantly, these numbers provide a starting point for thinking quantitatively about design problems. For example, a designer wondering how long to make a seat belt could make an initial estimate using the correlation in Table 2.4 and some knowledge of how heavy prospective customers might be. This would probably be easier than finding a representative sample of heavy people and measuring the circumference of their waists. | Age | Females | %Max | Males | %Max | |---|---|---|---|---| |1 | 74 | 46 | 75 | 43 | |5 | 110 | 68 | 111 | 64 | |10 | 138 | 86 | 138 | 79 | |15 | 160 | 99 | 168 | 97 | |20 | 161 | 100 | 174 | 100 | |35 | 161 | 100 | 174 | 100 | |40 | 160 | 99 | 174 | 100 | |50 | 159 | 99 | 173 | 99 | |60 | 158 | 98 | 172 | 99 | |70 | 157 | 98 | 171 | 98 | |80 | 156 | 97 | 170 | 98 | |90 | 155 | 96 | 169 | 97 | ## Basic Applications ### Design to Fit a Target Population 1. Identify the user population 2. Define the task and workspace and identify where human physical variability might place constraints on the design 3. Identify the body measurements that constrain the design 4. Specify the range of users to be accommodated 5. Calculate the range (see "statistical essentials") 6. Use the limits in (5) to specify the dimensions of the workspace The word "population" refers to groups of people sharing the following common factors: jobs; ancestors; occupations; geographical locations; age groups; race (ancestors); and ethnicity (culture, dress, customs, language, and so on). The criteria for deciding what constitutes a "target population" are functional and relate directly to the problem at hand-if we want to design a cab for bus drivers in Chile, we require data on the anthropometry of Chilean bus drivers. Consider product dimensions in human terms in view of the constraints placed on their design by body size variability, for example, seats should be wide enough for large users and low enough for small users. Body size and proportion vary greatly between different populations. A U.S. manufacturer hoping to export to Central and South America or Southeast Asia would need to consider in what ways product dimensions optimized for a large US population and probably male user group would suit Mexican or Vietnamese users. Ashby (1979) illustrated the extent of anthropometric variability as follows: If a piece of equipment was designed to fit 90% of the male US. population, it would fit roughly 90% of Germans, 80% of Frenchmen, 65% of Italians, 45% of Japanese, 25% of Thais and 10% of Vietnamese. Information about body size is not, in itself, directly applicable to a design problem. First, the designer has to analyze in what ways (if any) anthropometric mismatches might occur and then decide which anthropometric data might be appropriate to the problem. In other words, the designer has to develop some clear ideas about what constitutes an appropriate match between user and product dimensions. Next, a suitable percentile has to be chosen. In many design applications, mismatches only occur at one extreme (only very tall or very short people are affected, for example) and the solution is to select either a maximum or a minimum dimension. If the design accommodates people at the appropriate extreme of the anthropometric range, less extreme people will be accommodated. Matching product and user dimensions is important for reasons of safety, health, and usability. Botha and Bridger (1998) carried out an anthropometric survey of nurses in a hospital in Cape Town. They also captured data on problems of musculoskeletal pain and equipment usability. The anthropometric variables were divided into quartiles and the frequency of occurrence of problems was counted for each quartile. Many problems were found to be more common in the extreme quartiles. Table 3.5 summarizes the findings and demonstrates that many of the reported problems were caused or exacerbated by a work environment that did not fit its occupants. It is noteworthy that the sample of nurses in the study bore no resemblance to the local population of females in the Western Cape-many of them were not even from South Africa! It is often fallacious to assume that a group of workers in a particular occupational group are representative of the population of the parent country. If they are not representative, then anthropometric data from national databases (if available) cannot be used. An alternative approach (see below) is to use statistical scaling techniques to estimate the required anthropometric data. A basic set of strength data for pushing, pulling, and twisting is given in Table 3.6. Table 3.7 provides data on maximum grip and pinch strength for U.S. adults from 20 to over 75 years of age. These data may be of use considering the design trend of miniaturization made possible by microelectronics and resulting in smaller products. Figure 3.6 illustrates the three kinds of pinch action: tip pinch, where the thumb contacts the tip of the index finger, as in picking up a small object; key pinch, where the thumb pad touches the lateral aspect of the middle phalanx of the index finger, as when turning a key; and palmer pinch, where the thumb pad touches the pads of the index and middle fingers. Grip strength drops by about 20% from the age of 20 to 60 years and by about 50% by age 75 and above. For pinch strengths, the age-related reductions are not as large-75-year-olds having about 75% of the strength of 20-year-olds. | Reported problem/complaint | Associated anthropometric variable | |---|---| | Reaching for work objects | Low stature and grip reach | | Buying clothes | Large hip breadth | | Buying shoes | Foot breadth and length | | Lower backache | Large stature and abdominal depth | | Shoulder/arm pain | Low stature and grip reach | | Handles on equipment too small | Large hand and palm length hand breadth | | Handles that hurt the hands | Short hand length | | Work surfaces too low | High stature and standing elbow height | | Work surfaces too high | Low stature and standing elbow height | | Inadequate legroom in seated workspaces | High popliteal height and buttock-knee length | ## Anthropometry and Clothing Corrections Most anthropometric data are captured on nude or seminude subjects, whereas most workers wear clothing of some kind. The following corrections are often used: - Shoes: add 25 mm to stature - Hats and helmets: add 90 mm to stature - Protective clothing: add 40 mm to stature ## How to Deal with Anthropometric Constraints on Product Dimensions ### Find the Minimum Allowable Dimensions A high percentile value of an appropriate anthropometric dimension is chosen. When designing a doorway, for example, sufficient head room for very tall people has to be provided and the 95th or 99th percentile (male) stature could be used to specify a minimum height. The doorway should be no lower than this minimum value and additional allowance would have to be made for the increase in stature caused by items of clothing such as the heels of shoes, protective headgear, etc. ### Find the Maximum Allowable Dimensions A low percentile is chosen as in determining the maximum height of a door latch so that the smallest adult in a population will be able to reach it. The latch must be no higher than the maximum vertical grip reach of a small person. The height of non-adjustable seats used in public transport systems and auditoria is also determined using this principle-the seat must be low enough so that a short person can rest the feet on the floor when using it. Thus, the seat height must be no higher than the first or fifth popliteal height in the population. Figure 3.8 gives examples of some maximum allowable dimensions. Anthropometric data must always be used in a cautious manner, with a sound appreciation of the design requirements and the practical considerations. In particular, the designer should try to predict the consequences of a mismatch-how serious they would be and who would be affected. The height of the handle of a door leading to a fire escape in an apartment block dramatizes the seriousness of such mismatches-it is essential that a very wide range of users-including children-be able to reach and operate the handle in an emergency. The design of passenger seats for urban transportation systems is also important-although somewhat more mundane. Because the seats are used regularly by a very wide range of users even small imperfections will affect the comfort of a very large number of people every day. When using anthropometric data, the selection of a suitable cut-off point depends on the consequences of an anthropometric mismatch and the cost of designing for a wide range of people. One of the most important tasks is to predict and evaluate what any mismatches are going to be like. It is not normally sufficient only to specify the required dimensions without considering other aspects such as usability and misuse. | Pushing (N)* | Mean | Standard Deviation | |---|---|---| | Handle Height (m) | | | | 1.7 | 300 | 50 | | | 181 | 75 | | 1.3 | 337 | 83 | | | 221 | 103 | | 0.7 | 393 | 134 | | | 185 | 57 | | Pulling (N)* | Mean | Standard Deviation | | Handle height (m) | | | | 1.7 | 263 | 60 | | | 196 | 56 | | 1.3 | 347 | 55 | | | 223 | 80 | | 0.7 | 541 | 81 | | | 292 | 97 | | Wrist twisting Strength (Nm)* | Mean | Standard Deviation | | Males only, Knob diameter (mm) | | | | 9.5 | 52.75 | 12.8 | | 12.7 | 65.21 | 12.54 | | 19.1 | 111.65 | 26.2 | | | Males | | | Females | | |---|---|---|---|---|---| | | Mean | Standard Deviation | | Mean | Standard Deviation | | Grip strength | | | | | | | Right hand | 46.2 | 12.6 | | 27.9 | 7.6 | | Left hand | 41.4 | 12.3 | | 24.0 | 7.0 | | Tip pinch | | | | | | | Right hand | 7.6 | 1.8 | | 5.0 | 1.2 | | Left hand | 7.3 | 1.8 | | 4.8 | 1.1 | | Key pinch | | | | | | | Right hand | 10.9 | 2.0 | | 7.2 | 1.3 | | Left hand | 10.5 | 2.0 | | 6.8 | 1.4 | | Palmar pinch | | | | | | | Right hand | 10.4 | 2.2 | | 7.2 | 1.7 | | Left hand | 10.2 | 2.4 | | 7.0 | 1.6 | ## Activities/Assessments I. Know your body measurements and design the following according to such measurements. Explain and provide sketches or drawings. Show the measurements. a. Tops (Tee, blouse, polo, etc.) b. Shoes c. Bottoms (pants, shorts, skirt, etc.) d. Knapsack for guys, shoulder bag for girls e. Hat or baseball cap or helmet Format: Font- Arial, Size- 12, Spacing- Double ## References To know more about Anthropometry, browse through the following references: 1. Mark R. Lehto and James R. Buck; INTRODUCTION TO HUMAN FACTORS AND ERGONOMICS FOR ENGINEERS; © 2008 by Taylor & Francis Group, LLC Lawrence Erlbaum Associates is an imprint of Taylor & Francis Group, an Informa business 2. R.S. Bridger; Introduction to Human Factors and Ergonomics, Fourth Edition © 2018 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business