NOMOGRAM FOR THE QUICK GRAPHIC ESTIMATION OF FATNESS

Transcription

1 NOMOGRAM FOR THE QUICK GRAPHIC ESTIMATION OF FATNESS LIVIU DRAGOMIRESCU Abstract The paper presents a nomogram built for the quick determination of a subject s class of fatness. There are used here only the height and the weight of the subject. The classes of fatness are the ones defined by the World Health Organisation (WHO) using Body Mass Index (BMI). This nomogram can be also used for the quick estimation of the weight limits for normality or any other class of fatness. The information, friendly graphically-presented in only one page is equivalent to the one from the numeric table of almost 3 pages in the annex A of the work (1). The nomogram has been made with a computer program specially conceived by the author. A colour version can be found on the INTERNET at the addresses: Introduction Working at the volume (2), it became important to present the data necessary for fatness diagnosis in a both concise and suggestive manner. The WHO methodology in this matter recommends the use of BMI (Body Mass Index) and six levels for its values (1). These levels establish seven classes of fatness. The same methodology provides a table containing for each height, measured in an integer number of centimetres from 140 to 190 six levels of weight. In the case of normality, two more levels are indicated. Therefore, the table contains, besides the column for height, eight columns with value levels for weight. In all, that means 408 (=51 8) numbers and it takes almost three pages, grouped in the table A Consulting the table is relatively simple: Step 1. Fix the line were the subject s height is located. Step 2. On the fixed line, search the two weight values between the subject s weight is included. If the subject s weight is outside these values, the subject belongs to the respective extreme class. The general class of fatness for this weight can be read in the table heading. Then, consulting the end of the table, we can obtain the detail subclass. 1

2 Step2. In order to find the normality limits, read, on the same line, the values which, on columns, correspond to normality. For other classes, the procedure is analogous. The first two steps establish the class of fatness for a subject and the steps 1 and 2 determine the normality limits or, if needed, the limits for any other class of fatness for the subject. Although the utilisation of this table is not difficult, we believe that a graphic presentation of the same information is equally easy to use, but more attractive for most people. Material and method The material consists in the standard weight values according to the height, for the eight levels mentioned above. These values result from the levels established statistically for BMI and from the formula of this index. The BMI levels and the WHO classes for them are (1): Table 1. Levels for BMI and classes from (1). Body Mass Index underweight normality overweight , Table 2. Levels for BMI and subclasses from (1). BMI < 16 indicates very severe underweight 16 BMI < 17 indicates severe underweight 17 BMI < 18,5 indicates medium underweight 18,5 BMI < 25 corresponds to normality 25 BMI < 30 indicates medium overweight 30 BMI < 40 indicates severe overweight BMI > 40 indicates very severe overweight. We consider that the levels 20 and 22 determine the following subclasses of normality: 18,5 BMI < 20 normality tending towards underweight 20 BMI < 22 proper normality 22 BMI < 25 normality tending towards overweight. The formula for BMI is wt / ht 2. Wt is the measured weight in kilograms and ht is the measured height in metres. The method consists in the graphic synthesis in a nomogram of the table described in the introduction. For this, we plotted the height on the horizontal axis, the weight on the vertical axis, and within the graph we drew eight curves. Each curve represents pairs of values (height, weight) with the same BMI. For instance, the curve with the lowest location in Fig. 1 represents BMI = 16, the next, BMI = 17 and so on. The 9 zones delimited in plane by the 8 curves indicates the 9 classes of fatness. 2

3 Figure 1. Nomogram for the quick graphic estimation of fatness. Author: L. Dragomirescu. 3

4 Results The nomogram can be also used in the two problems for which the table A3. 10 from (1) was built: the determination of a subject s class of fatness and the indication of normality limits or of any other class, for that subject. In both matters, we begin with: Step 1. The identification of the vertical line showing the subject s height (in the example from Fig. 1, 168 cm). Then, in order to establish the class of fatness for a subject: Step 2. We determine the horizontal line corresponding to the value of the subject s weight (in example from Fig. 1, 75 Kg). We read the name of the zone where the two lines crossed - see the small square in the Fig. 1. To specify the normality limits, it follows: Step 2. The determination of the crossing points between the vertical line drawn at step 1 and the curves which bound the normality. Horizontal lines are drawn through these points, and the two values are read on the weight axis (indicated by arrows in Fig. 1: 52 Kg, respectively 71 Kg). We observe that in the table A from (1) there are given the values 52,2 Kg and 70,6 Kg. That means the graphic representation contains the information with an approximation of ± 0,5 Kg. Conclusions Generally, the weight of an adult subject is measured with a error higher than ± 0,5 Kg. Even if the subject is measured in standard conditions in the morning, on an empty stomach, nude or wearing bathing-costume - the presence or absence of bathing suit or the amount of water retained by the tissues according to the metabolism and the recent diet of the subject, as well as the error of the scales or of the operator lead to a error of the measurement higher than ± 0,5 Kg. Therefore, the approximation given by the nomogram is completely satisfying. The nomogram is much more suggestive, friendlier than the numeric table, the same as a classical clock with indicating hands is much easier to read than a modern one with digital display. This nomogram replaces in one page, three pages of digits. At the same time, it is also recommended instead of the nomogram proposed at the end of the work (1), which indicates graphically the BMI value. Then, the user has to consult the scale from the final of the annex A3. 10 in the same work that is the Table 2 above which is very complicated. Moreover, on that nomogram the normality limits (or the limits of any other class) can be read with much more difficulty, less intuitively and less precisely. In the end, we would like to inform you that a colour version of the nomogram hereproposed is available on the INTERNET at the sites: 4

5 References 1. OMS Utilisation et interprétation de l anthropométrie. Rapport d un comité OMS d experts. Série de Rapports techniques, Genève, Radu Elena, Glavce Cristina, Dragomirescu L. Ghid practic de antropologie. Vol. I. Iniţiere în antropometrie. In print. University of Bucharest, Faculty of Biology. 5