Response

Abstract

We wish to express our appreciation for Dr. Wagner's insight on the topic of subcutaneous fat thickness estimation through distinct methods, namely, skinfold calipers and ultrasonography (1). We agree with the major points raised in the letter to the editor but also wish to clarify some items related to the methodology. A major point is that both investigations used an existing ultrasound analysis software that incorporates, by default, the doubling of single-layer subcutaneous thicknesses prior to use in the Jackson-Pollock body density equation, as well as a tissue thickness estimate that includes skin thickness.Both the investigation of Tinsley et al. ( 2) and Chandler et al. ( 3) utilized a commercially available ultrasound technique, which includes analysis software (MuscleSound®, Glendale, CO). This manufacturer-rather than the individual investigatorsimplemented the methods of body composition estimation from ultrasonography data. This analysis software was used to increase the practicality of the current studies, as methods can easily be applied to both clinical and field settings.Personal communication with MuscleSound® (date: July 28, 2021), as well as verification in our own data, confirms that the analysis software simply doubles the single-layer subcutaneous tissue thickness, with the rationale that a skinfold caliper represents a double layer of tissue (4). We recognize that it is unlikely this process is without error and that there is evidence the ratio between an ultrasonography single-layer estimate and a skinfold double-layer estimate is not precisely 1:2 (5). Furthermore, we recognize the valid points raised in the letter to the editor regarding the varying, and often unknown, compressibility of skinfolds at distinct body sites. This contributes to the current inability to fully understand the practical significance of assuming a constant 1:2 relationship between thicknesses, as was implemented in our investigations. We recommend that commercial entities employing these procedures within their analysis software, as well as independent investigators, perform additional work to clarify whether it is appropriate to adapt skinfold-based methods to ultrasonography when estimating total body composition and what ratio most accurately represents the relationship at distinct body sites. If adapting caliper-based equations is ultimately deemed unsuitable, new equations should be developed and validated specifically with ultrasonography data. 190