The international protocol for anthropometric measurement is from a technical point of view periodically revised  in justification for the continuous updating of the literature. Comparative studies have investigated the reading time of skinfold thickness measurement , the physical-mechanical characteristics of plicometers , interchangeable anthropometric measurement approaches [5, 12; 22] and the location of the skinfold site .
A study carried out with a subsample of 62 male subjects observed that variation in the depth position of the plicometer contact jaws produced significant differences in triceps skinfold thickness (p < 0.05). The deep position resulted in thicker measurements and the superficial position resulted in less thick measurements, when compared to the middle position . Burkinshaw, Jones and Krupuwicz  found that marking the site of the four skinfolds in advance allowed examiners of varying degrees of technical skill to obtain consistent measurements. Subsequently, the importance of accuracy in locating the site of the eight skinfolds in a sample of 10 male subjects was investigated. Variations with significant differences in skinfold measurement values were observed for 70% of the peripheral grid points within a short distance of the defined criterion site .
The lack of analysis of the influence of measurement technique in the assessment of body composition or nutritional status is a methodological limitation of some comparative studies (4, 5, 12, 23]. Outcome classification is an important guiding variable for prescriptive interventions. The present study quantified the effect of different pinch sizes on the thickness of eight internationally standardized skinfolds in a sample of 29 subjects, totaling more than 1.800 points of morphological data, and on the consequent interference in the estimation and classification of body adiposity components.
The 6 cm-landmark showed similarity and statistical agreement with the subjective-landmark for all skinfolds, except the thigh, and with the sums of five and eight skinfolds. The 4 cm-landmark showed statistical similarity with subjective-landmark for triceps, supraspinatus and calf skinfolds, however, there was agreement only for appendicular skinfolds. The 8 cm-landmark showed similarity and statistical agreement with subjective-landmark supraspinal and abdominal skinfolds. Thus, it is suggested that skinfold thickness pinching at limb sites needs to be a smaller size (< 6 cm), except the thigh (> 6 cm), and trunk sites needs to be a larger size (> 6 cm).
The suggested opposite size between the lower appendicular sites is trivial. Martin et al. , in experiments with cadavers, it was evidenced that, regardless of gender, the thickness of the skin of the thigh is greater than that of the calf. Also, the static compressibility of the thigh is lower. Additionally, the larger musculoskeletal volume characteristic of the segment favors the increase of skin resistance to pinching, principally in subjects undergoing strength training.
The variability of the size of the pinch between the anatomical regions is justified by the intrinsic specificity of the density and compressibility of the skin-plus-subcutaneous adipose tissue of each site and subject, consequently affecting the technical-palpatory sensitivity of the anthropometrist and the degree of reproducibility of repeated measurements. The two aforementioned biological factors are inversely proportional [3, 21]. The negative linear relationship between skinfold density and compressibility partially explains the measurement variation observed between landmarks (Table 1), given that the site with high tissue density is less compressible and the site with low tissue density is more compressible. Therefore, pinching with subjective distance between the fingers is the one that best suits the quanti-qualitative variability of skinfold thickness and, in view of this, standardization of a fixed size of pinching seems to be improbable. And further, add to this the fact that, as described in Esparza-Ros et al. , the marking of the iliac crest skinfold site is performed from the technical-palpatory subjectivity with the subcutaneous tissue, making these parameters applicable to all other sites. It is suggested that the fixed-landmarks examined in the present study are not interchangeable for the measurement of skinfold thickness.
Systematic interference of skinfold thickness pinch size was observed in the estimation (Table 1) and classification (Table 3) of body adiposity components. The percentile classification of subcutaneous adiposity differed significantly (p < 0.0001) and the normative classification of reactive body fat was the least affected by the size of skinfold thickness pinching. However, independent of the way of classifying body adiposity, there was no agreement between the subjective-landmark and the fixed-landmarks (Table 3). It is noteworthy that when the measurement of skinfold thickness is not performed correctly, potential error is inflated, making the absolute values and estimates of the molecular-chemical and anatomical-tissue component of subcutaneous adiposity questionable and not applicable . Thus, it becomes necessary to standardize the measurement technique and undergo training with experienced tutors.
Access to the principal skinfold thickness measurement protocols is limited, especially in Latin American countries, as such protocols are described in book chapters [7, 9] that have not been reprinted and/or revised in the 21st century, or require participation in commercial refresher courses . The most relevant and instrumental information in the reference literature (6, 7, 9, 25], were compiled to facilitate reproduction by health and/or sport professionals who employ surface anthropometry in intervention scenarios.
These technical procedures have been revised, improved and operationally categorized into two steps: marking and measurement. All of which are sequentially performed on the right side of the body. The left hand should be used to pinch the site and the right hand to handle the plicometer regardless of the anthropometrist's lateral dominance. The use of anthropometric tape and a dermographic pen are essential for the marking stage. We suggest the use of a plicometer with a double spring system developed in accordance with the physical-mechanical characteristics of the prototype proposed by Edwards et al.  and described in Tanner and Whitehouse .
Marking Step: I) Identify and accurately mark the skin fold site (Fig. 1A-S); II) Mark the line of the vertical, oblique or horizontal anatomical axis of the skinfold (Fig. 1A-L1) and a perpendicular line forming an intersection (Fig. 1A-L2); III) In the direction of the anatomical axis, mark a short guideline for the position of the plicometer's contact jaws at 1 cm from the site (Fig. 1A-L4). [Note: this line ensures that the plicometer jaws are positioned in the same location in repeated measurements.]; IV) Perform pinching on the contact area of the site with the left index finger and thumb tips flexed, perpendicular to the anatomical axis, in order to become familiar with the skin-plus-subcutaneous adipose tissue. [Note: increasing pinching size is suggested (< to >) until two parallel layers of tissue are properly joined without excessive stretching of the skin in the outer region of the pinch]; V) Subjectively define the size of the skinfold thickness at the site, keeping it held, then undo it keeping the fingers in contact with the site, and finish by marking the chosen pinching size with two short vertical lines (Fig. 1A-L4). A demo with images is provided in the Supplementary Material.
Measuring Step: I) Position the fingertips on the guidelines (Fig. 1A-L4), then pinch and firmly detach the skinfold, with the back of the hand facing the anthropometrist, just above the intersection and perpendicular to the anatomical axis; II) Apply the plicometer contact jaws on the short guideline (Fig. 1A-L3) and at median depth proportionally to the middle of the fingernail. [Note: this depth is also understood as the alignment between the distal interphalangeal curve of the thumb and the curve of the fixed rod of the plicometer.]; III) Carefully observe the measurement resolution scale and then gradually release the plicometer trigger, keeping the skinfold firmly held; IV) Take the measurement reading 2 seconds after complete pressure is exerted by the plicometer spring system; V) Carefully remove the contact jaws, activating the plicometer trigger and then releasing the skinfold.
A minimum of two sequential measurements should be taken at each skinfold site. The mean value is used. In the event of a technical measurement error of > 5%, a triplicate is performed and the intermediate value used for the site that presents this variation. After finishing the measurement step, the landmarks should be cleaned with a moistened tissue.
This study involved intentional sampling and not representative of the morphological heterogeneity inherent in the population investigated. Therefore, the results are limited, in their ability to generalize, to groups with characteristics at the extremes of skinfold thicknesses composition and compressibility. Additionally, the lack of statistical analysis stratified by gender has been highlighted, which consequently limits the understanding of the results regarding sexual dimorphism.
The experimental evidence from this study is important in updating the internationally standardized skinfold thickness measurement technique. It is suggested that the anthropometrist identify and mark in advance, not only the site, but also the size of the pinch with subjective distance between the fingers.