Skinfold thickness varies directly with spring coefficient and inversely with jaw pressure.

PURPOSE: The main aims of this study were to: 1) determine whether heavy use of Harpenden calipers caused deterioration of the spring coefficient (force per unit length), 2) to quantify the change in skinfold thickness per unit change in jaw closing (downscale) pressure, and 3) to develop a calibration range for these calipers. METHODS: Part a) The change in spring force per unit length after at least 100,000 cycles of opening and closing five different springs was measured on a load cell. Part b) The dynamic downscale jaw pressure exerted by six pairs of Harpenden springs was measured on one caliper. Two were new pairs of springs (N1 and N2), two were 25-yr-old springs (O1 and O2), and two pairs (S1 and S2) had been used for less 1 yr. The six spring pairs were used to measure skinfold thicknesses at nine sites, in triplicate, on 20 subjects with the order of springs randomized and counterbalanced. Part c) The downscale jaw pressure of 78 Harpenden calipers was measured at eight jaw gaps. RESULTS: Part a) The springs did not change their characteristics after >100,000 cycles. Part b) At each skinfold site, the lowest thickness was recorded for S2 which exerted the highest jaw pressure (9.04 g x mm(-2)) and conversely the highest thickness was for N1 which exerted the lowest jaw pressure (8.02 g x mm(-2)). Increasing the downscale jaw closing pressure from 8.0 to 9.0 g x mm(-2) reduced a skinfold thickness by approximately 10%. Part c) The mean downscale jaw pressure was 7.82 +/- 0.25 g x mm(-2). CONCLUSIONS: In summary, it is suggested that if accurate skinfold measures between different Harpenden calipers are required, the downscale jaw pressure should be in the range of 7.40-7.82 and 7.85-8.21 g x mm(-2), at jaw gaps of 5 and 40 mm, respectively. These jaw pressures can be achieved by servicing the caliper pivot and indicator gauge to minimize frictional losses, adjusting the caliper jaw alignment, and by selecting springs that have a spring coefficient in the range 1.10-1.15 N x mm(-1).

Apparatus for precision calibration of skinfold calipers.

Despite the fact that skinfold calipers are widely used to measure subcutaneous adipose tissue, the current methods of calibration are quite crude. Methods such as hanging masses from the caliper jaws until they remain open, lack validity and reliability because the caliper jaws are stationary instead of dynamic, and the opening jaws give an upscale reading of the jaw gap not a downscale reading that occurs when the calipers are being used to measure skinfolds. This report describes how to build an apparatus capable of measuring static and dynamic, upscale and downscale jaw pressures of a variety of caliper types and also provides guidelines specifically for calibration and servicing of Harpenden calipers. The key areas to maintain are the caliper springs (which should have spring coefficients ranging 1.104-1.153 N.mm-1 ), the pivot joint (which should operate smoothly), the indicator mechanism (which should require only 0.78-0.88 N for full movement), and the jaw alignment which should be square to ensure that the full effective jaw surface area of 90 mm2 is applied to the skinfold. While there are insufficient data at this time to prescribe rigid calibration criteria, assessment of approximately 100 new and used Harpenden calipers indicates that, after servicing, the important dynamic downscale jaw pressure will range 7.7-8.4 g.mm-2 at 5 mm of jaw gap and 7.3-8.0 g.mm-2 at 40 mm of jaw gap. Dynamic upscale jaw pressure should be within 1.0-1.5 g.mm-2 of the corresponding dynamic downscale jaw pressure. Am. J. Hum. Biol. 10:689-697, 1998. © 1998 Wiley-Liss, Inc.

A microcomputer system for physiological data collection and analysis.

The ability to monitor and record activity within the masticatory system is of importance to both general practitioner and research worker. Recent developments in physiological data collection and analysis at the Department of Anatomy, University of Queensland, have achieved that objective in a simple and cost-effective manner. Recording, printing, plotting, and a wide range of analysis procedures can be undertaken utilizing relatively inexpensive available computers.

Calibrating skinfold calipers.

While athletes are routinely assessed for changes in subcutaneous adipose tissue with skinfold calipers, absolute dynamic calibration of caliper jaw compression is currently not possible. The first part of this study describes how dynamic compression of foam rubber blocks can be used to monitor the relative calibration of a single pair of calipers as springs fatigue, or to alert an investigator to variations in measurement values between different calipers. The second part of the study, carried out on 10 female athletes, demonstrated that the significant differences established by the foam block method of calibration also translated into a significant difference for the sum of seven subcutaneous skinfolds. Foam blocks can be used as a simple, inexpensive method to establish a calibration range and can also be used to recheck calipers periodically, depending upon their use.