Browsing by Author "Breytenbach, Johannes Gerhardus"

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    The influence of skin thickness on the determination of the percentage of body fat (skinfolds and ultrasound)
    (Stellenbosch : Stellenbosch University, 1996-03) Breytenbach, Johannes Gerhardus; Blaauw, J. H.; Stellenbosch University. Faculty of Education . Dept. of Sport Science.
    ENGLISH SUMMARY: There are several ways to assess the body composition of young men in a laboratory setting. However, due to the invasiveness, expense, time, specialised equipment, extensive instrumentation and level of skilled personnel required to perform these methods, they are generally not used in a clinical setting. New methods are being developed for clinical use, which may offer the potential for non-invasive, not too costly in terms of time and equipment, reliable and easy body composition estimate. These methods involve the development of formulae which relate skinfold or circumference measurements, or a combination of both, to indirect estimates of body fat (Drinkwater, 1984: 17). Since many of these methods involve the determination of the adipose tissue in vivo, most techniques rely on external body measurements through the skin. The importance of the influence or contribution of the actual skin thickness on the determination of the caliper skinfold thickness has rarely been investigated. Ultrasound or sonar scans proved to be a fairly non-invasive and inexpensive, not too time consuming, yet accurate method to determine the skin and subcutaneous fat layer individually in human beings. Various tests were performed on the subjects, such as hydrostatic weighing, lung functions, bio-electrical impedance analysis and a vast range of anthropometrical measurements including weight, stature, diameter, girth and skinfold (caliper), skin and fat (sonar) on fourteen body locations were recorded. The body density values (skinfolds), according to Durnin & Rahaman (1967) and Jackson & Pollock (1978), were individually applied to the formulae of Brozek (1953) and Siri (1961) to calculate the percentage body fat. Correlations with hydrodensitometry were high, ranging from r=O,81499 (for Durnin & Rahaman and Brozek) to r=O,82338 (Jackson & Pollock and Siri) (see Figures 10 to 13). The same procedure was followed with the sonar measurements and different combinations such as fat, 1x skin + fat and 2x skin + fat, were used. Correlations with hycfrodensitometry were remarkably high, seeing that these formulae were developed for the use of skinfold calipers, and ranged from r=O,77198 (Durnin &' Rahaman and Brozek) to r=O,84545 (Jackson & Pollock and Siri) (see Figures 14a to 17c). When applying the sonar (fat) measurements to the formula of Jackson & Pollock, it resulted in a relatively higher correlation (r=0,8455), as when compared to other combinations of sonar measurements, namely sonar (1 x skin + fat) and sonar (2x skin + fat), which resulted r=0,83697 and r=0,81987 respectively. When substituting the supra iliac (anterior) and medial thigh body locations with the supra iliac (posterior) and anterior thigh values respectively, a good correlation (r=0,83575) was found. Although all of these variations yielded good results, it can be seen that the formula of Jackson & Pollock was developed for the use of skinfolds (r=0,89224). When substituting the supra iliac (anterior) and anterior thigh body locations with the supra iliac (posterior) and medial thigh values respectively, a good correlation (r=0,86924) was found. This indicated that more attention should be given to these areas of fat deposits formerly not investigated, especially the medial thigh for females, and the posterior supra iliac for males. Each of the 14 body locations was individually correlated with body density via three different methods, namely skinfold measurements (Harpenden caliper), fat measurements (sonar) and 2x Skin and fat: (sonar). Skinfolds correlated the highest with body density, ranging from r=0,827 (abdomen) to r=0,615 (bicep). The second highest correlations were found to be that of fat thickness, varying from r=0,791 (tricep) to r=0,237 (chin). The sonar measurements (2x skin + fat) correlated third highest ranging from r=0,754 (chest) to r=0,239 (chin). Subsequently no ultrasound formulae were available to compare this population group and a new regression equation, using seven sonar fat values, was developed to indirectly estimate the body density. These findings were compared to and correlated with hydrodensitometry (r=0,86784) (see Fig, 29). A further regression equation was developed, using the sum of seven skinfolds as measured by caliper, in order to predict body density. This equation was also compared to hydrodensitometry and yielded a correlation of r=0,86936 (Fig 30). Either method of measurement and accompanying formula yielded good results when compared to hydrodensitometry providing that the subject qualifies for the 18 to 30 year old endo-mesomorphic category. This study provides the health professional with alternatives where a choice between sonar and skinfold measurements can be made, depending on the preference of the patient and clinician or the time and apparatus available.