Regression Models of Some Anthropometric Dimensions Based on Stature: A Case Study among Students 18 to 26 Years

Abstract  Background and Purpose Anthropometric data is an essential part of the ergonomics design of the equipment, environment and work. Using anthropometric information, designers will be able to design appropriately the needs of the dimensional characteristics of the target group. According to studies, the structural characteristics of the human body are influenced by factors such as race, age, gender and type of nutrition, and vary in different nations. Several studies have shown that anthropometric data varies in different societies. Comparing the body ratios of male and female workers in some Asian countries, including Iran, shows that most aspects of the mean and all body ratios have significant differences. It is important to note that despite the high accuracy and low cost of direct measurements of anthropometric dimensions and the existence of extensive databases about them in different societies, there are still numerous problems in direct measurements of anthropometric dimensions of individuals, some of which include: the need to train individuals before measuring the dimensions that are time consuming and with their specific problems, interference in the activities of individuals and, consequently, the possibility of lack of proper collaboration in measuring the dimensions, requires the measurement of dimensions by the homosexual person, especially in Islamic countries, due to the cultural and ethical issues of those societies, and the discontent of most people, especially when it comes to repeat the measurements. Therefore, the role of the use of indirect methods, including the use of biometric regression relations, is more important for estimating the anthropometric dimensions of the target community. The advantages and limitations available for each of the commonly used anthropometric measurements on one hand, and the particular conditions of real working environments, especially in developing countries such as Iran, where physical problems and physical damage are due to poor design, on the other hand, it has led to the need for a fast, convenient, acceptable, and non-interfering procedure for workers to determine the anthropometric dimensions necessary. In this regard, attention to the biometric relationships of physical dimensions can be useful. Because in the case of finding a meaningful relationship between one or more anthropometric dimensions with other physical dimensions, it is possible to provide the anthropometric characteristics with a high degree of certainty by little time and cost and without the need for specialty. Several studies have used biometric relationships between different dimensions in the areas of forensic medicine, identification, dentistry, etc. But focusing on ergonomics and anthropometrics in designing tools and equipment in work environments has been less addressed in this area. On the other hand, researches has also been limited to small communities and cannot be generalized to the general Iranian community due to the wide diversity of ethnic and racial diversity. So, researchers have considered further studies in this area necessary. Therefore, this study aims to investigate and determine the ratio of some of the anthropometric dimensions of the indicator, which is used in various designs used by ergonomics and industrial designers, in sitting and standing static situations and in two groups of students in the age group of 18 to 26 years old.   Methods In order to achieve the goals of the study, demographic data were first collected through questionnaires. The dimensions of the study included 20 positions in standing position and 18 dimensions in sitting position. Anthropometric measurements were done using caliper, tape measure, balance and checkerboard sheet (Anthropometer). To increase the assurance of measurements, multiple dimensions were selected randomly and measured by two people. The results of this study were analyzed using correlation coefficient test and if there were no significant differences between measurements by different individuals, the study continued until the end. Otherwise, training was needed for the correct examination method to be uniformed and measurements are repeated. 206 people, including 162 women and 44 men, were enrolled in this study. Sample subjects were selected randomly and clustered among male and female students. According to the main goal of the study, people with severe abnormal BMI, people with a history of musculoskeletal disorders or congenital disorders, people with severe diets, pregnant women and athletes were excluded. In order to increase the accuracy of measurements, all measurements were made in standing and sitting conditions, in a non-shoe mode and with a minimum of clothing (underwear). Also, in order to avoid interference with the measurement of some physical dimensions due to lunch, the time of measurements was selected between 8:00 and 12:00. The accuracy of the measurements was considered to be 0.1 cm in all dimensions. The results of the study were analyzed using SPSS 22 software. In this study, the distribution of anthropometric data was performed using dispersion indices and percentiles 5, 50 and 95, as well as mean and standard deviation. Also, to investigate the biometric relationships of different dimensions in relation to the height dimension of individuals in the population, multiple regression models were used. In these models, the biometric relationship of various dimensions of the body based on height dimension, which was easily measured, was examined in static sitting and standing positions.   Results The results of demographic information analysis of the subjects were studied in two groups of gender and in the age range of 18 to 26 years old. Also, the 5th, 50th and 95th percentiles and standard deviations of measured dimensions in standing and sitting subjects and gender were presented, respectively. In general, 12 regression equations were obtained for standing dimensions relative to height in women and 14 regression equations for standing dimensions relative to height in men. The corresponding values ​​for sitting dimensions were 14 and 12 for men and women, respectively. In accordance with the main objective of the study which was finding relationships between the anthropometric dimensions of individuals in static states to estimate and predict other anthropometric dimensions of a person, the findings of this study showed that the mean and standard deviation of most anthropometric data in women and men have a significant difference with each other (P <0.05), and in general, its values ​​in women were smaller than males. Also, comparison of 5, 50 and 95 percentiles in standing and sitting anthropometric dimensions showed that there was a significant difference between static anthropometric dimensions in standing and sitting position in both gender groups. So that the standing dimensions in men were more than women in all three percentiles. However, in the dimensions of sitting, the amount of this difference is reduced and in some cases, such as head length, depth of chest, and abdominal depth, there is no significant difference in the 5, 50 and 95 percentiles of men and women were seen. The findings of the existing regression relations between the different static standing anthropometric dimensions and the selected index in this study, which was the height of the subjects, also showed that there is not a significant correlation between height and anthropometric dimensions of the width of the hand, the internal and external distance between the two eyes and the width of the wrist in women. In the 95% confidence interval among women, standing grip reach, length of upper limb and elbow height with correlation coefficients of 0.791, 0.742 and 0.737 have shown the highest fit with height dimension and other dimensions have shown moderate and weak correlations with dimensional dimensions. In men, the shoulder height, eye height and length of upper limb showed the highest relationship with height with correlation coefficient of 0.949, 0.867 and 0.840, respectively. Comparison of the coefficients of correlation obtained in the two gender groups also shows that in most of the dimensions measured in standing position in men, there are more correlation coefficients than women. Also, in terms of the number of dimensions, more dimensions in men than women with a height dimension have been meaningful. The relationships between different dimensions of body and height of people in this study and the appropriate and acceptable correlation coefficients obtained between the many dimensions such as eye height, shoulder height, elbow height, knuckle height, upper limb length, shoulder-grip length, standing grip and buttock knee length, with the height of the individuals, can be indicative of the fact that acceptable estimates of the dimensions can be obtained by measuring only the height of people. From the total of 38 anthropometric dimensions studied in this study (20 standing and 18 sitting positions), 26 regression relations were statistically significant (P <0.05) at 95% confidence interval for both men and women groups, separately. Although the relationships were statistically significant, they did not include the same dimensions in the two gender groups. For example, in women, sitting height and sitting shoulder height were significant and had a regression relation, but in men, no significant relationship was found between these dimensions. Conclusion Due to the limitations of anthropometric measurements during design, the use of biometric relationships can be proposed as a practical, rapid, and acceptable alternative of indirect methods. Based on the results of this study as well as other similar studies, it can be seen that stature can be considered as a suitable indicator and predictor dimension in designs that require specific body dimensions such as shoulder height, eye height, standing grip, upper limb length and elbow height. However, given that the study was conducted in a small student population, and it was not possible to select the same number of people from two groups of gender, it is suggested that, in order to increase the accuracy of the work and the reliability of the results, the complementary and targeted studies should be developed and implemented in the following the present study. So, it is expected that the anthropometric predictive tools such as a predictive software can be obtained so that, by measuring the minimum dimensions of each person as inputs, other dimensions required for design would be estimated, reasonably. Also, although examination of a large number of sitting and standing positions in this study compared to other studies has been considered as one of the strengths of the present study, it is recommended that in later studies, in addition to the relationship between dimensions measured and stature, relationships between stature and other anthropometric dimensions, which can easily be measured, is to be considered.