Static and dynamic differences among five types of skinfold calipers.

Thirty-eight skinfold calipers were compared in terms of dial accuracy, downscale force, and pressure at jaw openings of 10, 20, 30, 40, and 50 mm. Dynamic measures were made on four thicknesses of foam rubber. Foam rubber was used to simulate the compressibility of skinfolds and to eliminate subject and tester variability. Five caliper types were tested: 10 Harpenden (HRP), 9 Lange (LNG), 12 Slim Guide (85SG), 4 Skyndex (SKN), and 3 Lafayette (LF). Within-type variation was small and consistent across openings for dial accuracy, force, pressure, and foam rubber compressed thickness. Between-type pressures differed (p less than 0.01), with the HRP and LNG calipers having the highest but similar pressures and the SKN, LF, and 85SG calipers having the lowest but similar pressures. LF and LNG calipers (which differed from each other) had higher compressed foam rubber means than HRP, SKN, and 85SG calipers (p less than 0.01), which were similar to each other at three of four thicknesses. When average pressure was used as the covariate, differences between types were still large, with 97.5-99.3% of the variation explained by type. Compressibility of foam rubber was shown to be caliper specific. It is concluded that there are static and dynamic differences between the five major types of skinfold calipers. When measurer error is eliminated, the HRP, 85SG, and SKN calipers are similar to each other, but they give lower values than the LNG or LF calipers by approximately 50-100%, depending on compressed thickness. These differences should be noted when comparing skinfolds measured with dissimilar calipers.