Background: The aim of this study was to analyze the validity of four different skinfold calipers, as well as to establish the differences between them in a healthy young adult population. Methods: The present study followed a cross-sectional design, including 138 participants, with 69 males (21.46 ± 2.52 years) and 69 females (22.19 ± 2.85 years). The measurement protocol included basic measurements of body mass and stretch stature and eight skinfolds with a Harpenden, Holtain, Slim Guide, and Lipowise. The ∑6 and ∑8 skinfolds and fat mass were calculated. The order in which the skinfold calipers were used was randomized. Results: No significant differences were found in either the Σ6 and Σ8 skinfolds or masses and fat percentages calculated with the skinfolds obtained with the different calipers (p > 0.05), and the inclusion of the covariates of sex, BMI, and hydration status of the participants showed no effect on the differences. The Bland–Altman test showed significant differences between the calipers (p < 0.001). Conclusion: It has been observed that the analyzed calipers have shown validity for the assessment of adiposity-related variables in a male and female sample of non-overweight, young healthy adults, but they are not interchangeable with each other when the assessment is meant to be compared over time or with other samples.

Summary: Obesity has been linked to several physiological and psycho-social diseases, decreases in cognitive function, poor levels of scholastic achievement, low socioeconomic status and delayed onset of maturity. This study investigates the association between obesity and both academic performance and reasoning ability in 394 male and 398 females students between the ages of 6 and 12 from Lisbon, Portugal. It also assesses how this relationship may be influenced by chronological age, maturity and socioeconomic status. The results suggest that: 1) reasoning ability is independent of socioeconomic status and level of maturity; 2) no differences in reasoning ability exist between groups of different BMI; 3) academic performance is moderated by chronological age in boys, and by maturity in both genders; 4) obesity is not associated with academic performance. It is concluded that reasoning ability and academic performance are not associated with obesity, and that inter-individual differences in academic performance in boys may be explained by differences in their level of maturity.

The skinfold caliper reading of the skinfold thickness depends on its dynamic compressibility. This has led to the fact that, while it is indicated that skinfold readings should be taken when the reading is stable, there is no consensus on at what second the reading should be taken after the application of the skinfold caliper. The new Lipowise PRO digital skinfold caliper was used to analyze the evolution of skinfold readings under skinfold caliper pressure. The aim of the present investigation were: a) to analyze the evolution of the reading time of individual skinfolds when subjected to skinfold caliper pressure and when the skinfold reading reaches stability; b) to describe the physical behavior of skinfold tissues’ time response to skinfold caliper pressure, and to explore differences between sites and subjects’ skinfolds compressibility; and c) to analyze the sex differences in both the reading and the evolution of the skinfold over time. A descriptive cross-sectional design was followed with a convenience sample of 165 healthy young adults (79 males and 86 females), with eight skinfolds measured using the Lipowise PRO skinfold caliper. The Lipowise PRO skinfold caliper uses a programmable reading time allowing for the measurement of the skinfold’s thickness at a rate of 100 times per second, and monitoring skinfold behavior over the 3-second measurement period, thereby enabling the assessment of the tissue response to the constant force exerted by the skinfold caliper jaws. All skinfolds showed statistical differences in terms of compressibility characteristics (p < 0.001). Significant differences were found between measurement time points for individual skinfolds and sum of skinfolds (p < 0.001–0.025). Stabilization being found depending on the skinfold measured from 1.5 seconds for biceps, subscapular, iliac crest, supraspinale, abdominal, and thigh skinfolds; 2.0 seconds for ∑6 and ∑8 skinfolds; and 2.5 seconds for triceps and calf skinfolds. It was observed an effect of sex on this issue (p < 0.001–0.030). More specifically, in the case of males, the supraspinale and abdominal skinfolds stabilized after 1.5 seconds; the calf skinfold and ∑6 and ∑8 skinfolds stabilized after 2 seconds; while the rest of the skinfolds did not stabilize until 3 seconds. In the case of females, no stabilization of the triceps skinfold was found, while the rest of the individual skinfolds and the ∑6 and ∑8 skinfolds stabilized from 1.5 seconds. A regression analysis indicated that skinfold thickness could be predicted based on measurement time in 50–77% of the cases (p = 0.001). A skinfold caliper application, using the digital caliper Lipowise PRO, of three seconds may be sufficient for achieving stability in the measurement and for obtaining the minimum value for most individual and sum of skinfolds. However, there are certain skinfolds that may require more time when performed on certain individuals, which vary according to sex.

Background: This cross-sectional study aims to clarify the relationship between coaches’ decisions and players’ relative age, biological maturation, and experience when identifying Under-14 (U14) players for the District and National Teams. Methods: A total of 360 male soccer players participating in the U14 national inter-association tournament, Lopes da Silva, were assessed. Birth dates were recorded, and players were categorized by birth quarter. Anthropometric measurements, fitness level (handgrip strength), and success indicators (performance evaluated by the coach, minutes played, and selection for the National Team) were documented, Maturation status was determined using bone age. Results: The majority of the sample was born in the 1st and 2nd quartiles regardless of maturation status. Morphological and functional differences between players born in different quartiles were no longer significant after controlling the effect of bone age. Late-maturing athletes played significantly fewer minutes. Among the players selected for the National Team, 89.9% were early or on-time maturers, and 92.9% were born in the first or second quartile of the year. While previous studies have shown reduced variability between bone and decimal age in the third and fourth quartiles, our findings indicate greater variability across all birth quartiles. Conclusions: Maturation status and relative age effect are crucial factors influencing coaches’ selection decisions. These findings highlight the need for a more equitable approach to talent identification, which should include track maturation bias avoiding the pursuit of short-term success and promoting long-term development programs for young soccer players. Undoubtedly, maturation status and relative age effect (RAE) play a significant role in a coach’s decision-making process.