Bioimpedance parameters in adolescent athletes in relation to bone maturity and biochemical zinc indices.

Phase angle (PA) is derived from resistance and reactance determined by bioimpedance analysis (BIA) and it appears to relate to cellular stability and integrity. Interpretation of PA values could be complemented by bioelectrical impedance vector analysis (BIVA), which relates to body hydration and structure. Body composition, age, sex, and nutrients are known to stabilize cell membranes, such as zinc, have been related to PA although information is scarce in adolescent athletes. The aim of the present study was to assess the association of body composition, skeletal maturity and zinc biochemical indices with phase angle and bioelectrical impedance parameters, in forty male adolescent soccer athletes (13.4±0.6years). BIA was performed with a single-frequency tetrapolar analyzer. PA and BIVA were determined using resistance and reactance BIA data. Plasma and erythrocyte zinc concentrations were measured using inductively coupled plasma-optical emission spectrometry. Body composition was determined by dual-energy X-ray absorptiometry, and bone age by hand X-ray measurements. PA was higher in adolescents classified by bone age as "Early" (6.8±0.9°) compared to "Late" (5.7±0.5°) (p<0.05). PA correlated with bone age (r=0.562), BMI (r=0.382), fat-free mass (r=0.468), and erythrocyte zinc (r=0.379) (p<0.05). BIVA confidence ellipses were sensitive to skeletal maturity status. Phase angle was higher in adolescents with erythrocyte zinc concentration above the median (>0.66µmol.g hemoglobin-1) compared to those below the median. Multiple linear regression analysis showed that bone age (B=0.254, p=0.001) and erythrocyte zinc concentration (B=1.168, p=0.047) were significantly related to PA in this group, and accounted for 34% of its variability. Our results indicate that bone age and zinc erythrocyte contribute to PA values in the young male soccer athletes and that BIVA is influenced by skeletal maturity status in this group.

Biological maturation assessment methods in adolescent soccer players considering zinc status / Métodos de evaluación de la maduración biológica en jugadores adolescentes de fútbol considerando el estado de zinc

SUMMARY: The purpose of this study was to compare different methods of maturity evaluation and their relation with performance-related physical and anthropometric variables in young soccer players, with different plasma zinc status. A total of 53 healthy male young soccer players (age: 13±1 years; body mass: 48±10 kg; stature: 160±10 cm) participated in this study. Variables from physical fitness (stature, ST; fat-free mass, FFM; handgrip strength in the dominant hand, DHS), testosterone and zinc plasma concentration were measured. Biological maturity was evaluated by sexual maturity (development of: pubic hair, PH; genitals, GD; axillary hair; AH), bone maturity (TW3 method; BA), and testosterone plasma concentration methods. We observed that: (i) the frequency of hypozincemics and normozincemics children stratified by BA-CA, PH and GD were similar in each category; (ii) the BA allowed the identification of differences between the three categories, in at least two performance-related variables (FFM and DHS, p<0.0001); (iii) the AH method was able to discriminate only for DHS (p<0.0001); and (iv) the testosterone method was not able to identify differences between the four maturation categories with regard to ST, FFM, and DHS. Results suggested that Zinc deficiency did not influence the results obtained for the maturation categories defined by the different assessment methods. The assessment of biological maturation by BA seems to be the most effective for the stratification of performance-related and anthropometric variables in young soccer players. Nevertheless, the AH method should also be considered as a fair option to be used in field studies and practice.

RESUMEN: El objetivo de este estudio fue comparar diferentes métodos de evaluación de madurez y su relación con variables físicas y antropométricas relacionadas con el desempeño en jóvenes jugadores de fútbol, con diferentes niveles plasmáticos de zinc. Participaron en este estudio 53 jugadores de fútbol jóvenes sanos (edad: 13 ± 1 años, masa corporal: 48 ± 10 kg, estatura: 160 ± 10 cm). Se midieron las variables de la aptitud física (estatura, ST, masa libre de grasa, FFM, fuerza de agarre en la mano dominante, DHS), testosterona y concentración plasmática de zinc. Se evaluaron la madurez sexual (desarrollo de vello púbico, PH, genitales, DG, cabello axilar, AH), madurez ósea (método TW3, BA) y concentración plasmática de testosterona. Se observó que: (i) la frecuencia de los niños hipoxincémicos y normozincémicos estratificados por BA-CA, PH y GD fueron similares en cada categoría; (ii) el BA permitió la identificación de diferencias entre las tres categorías, en al menos dos variables relacionadas con el desempeño (FFM y DHS, p <0,0001); (iii) el método AH fue capaz de discriminar sólo para DHS (p <0,0001); y (iv) el método de testosterona no fue capaz de identificar diferencias entre las cuatro categorías de maduración con respecto a ST, FFM y DHS. Los resultados sugirieron que la deficiencia de zinc no influyó en los resultados obtenidos para las categorías de maduración definidas por los diferentes métodos de evaluación. La evaluación de la maduración biológica por BA parece ser la más efectiva para la estratificación de variables de rendimiento y antropométricas en jóvenes jugadores de fútbol. Sin embargo, el método AH también debe ser considerado como una opción justa para ser utilizado en estudios de campo y práctica.

Methodological agreement between body-composition methods in young soccer players stratified by zinc plasma levels / Acuerdo metodológico entre los métodos de composición corporal en jugadores jóvenes de fútbol estratificados por los niveles plasmáticos de zinc

It is feasible to think that the body composition assessment may be influenced by maturational and zinc status, especially in young athletes, which perform regularly high volume of physical training. In accordance, it seems important to clarify the impact of these factors in body composition assessment in athletes, since errors may lead to mistakes in training prescription and diet elaboration, and therefore affect the athletic performance. The objective was to compare (1) different methods of body composition evaluation in young soccer players stratified by zinc plasma levels; and (2) the two reference methods using skinfolds thickness in children (Slaughter's and Lohman's equations), considering the maturation level. In this cross-sectional study, fifty tree young soccer players (13.3±0.7 y) were submitted to blood collection, electric bioimpedance (BIA), dual energy X-ray absorptiometry (DXA), anthropometric measures (body mass, stature and skinfolds thickness (ST)) and hand-wrist X-ray. Body composition evaluation was performed by: DXA, ST (Lohman and Slaughter equations) and BIA (Houtkooper equation) methods. Zinc status provided two groups: Normozincemic and Hypozincemic athletes, determined by cut-off point of 11.0 µmol/L. Significant difference on descriptive data for all participants after zinc status stratification was observed only for plasma zinc concentration; (2) Significant correlations were observed between the assessment methods (fat percentage: r= 0.34 to 0.98 and p<0.001 to 0.013; fat free mass: r= 0.95 to 0.9998 and p<0.001), and lowers correlations were observed when electric impedance was involved; and (3) Bland-Altman plots across methods showed a closer agreement when DXA and ST were compared. In conclusion (1) The ST method was better than BIA to assess the body composition (in young soccer players) when DXA scans are not available; (2) The comparison of models based on ST showed that the best association with the values from DXA were obtained for the Slaughter equation, followed by the Lohman equation using bone age instead of chronological age; and (3) Plasma zinc levels seem not to influence the body composition assessment, which certainly warrants further studies.

Es factible pensar que la evaluación de la composición corporal puede estar influenciada por el estado de maduración y los niveles plasmáticos de zinc, especialmente en atletas jóvenes, que regularmente realizan un alto volumen de entrenamiento físico. Por tanto, es importante aclarar el impacto de estos factores en la evaluación de la composición corporal de los atletas, ya que errores en su análisis pueden conducir al desarrollo de una equivocada prescripción de entrenamiento, además de una dieta determinada, y por lo tanto afectar el rendimiento deportivo. El objetivo de esta investigación consistió en: (1) comparar los diferentes métodos de evaluación de la composición corporal en futbolistas jóvenes estratificados por los niveles plasmáticos de zinc; (2) comparar los dos métodos de referencia utilizando el espesor de los pliegues cutáneos en niños (ecuaciones de Slaughter y Lohman), teniendo en cuenta el nivel de maduración. En este estudio transversal, cincuenta futbolistas jóvenes (13,3±0,7 años) fueron sometidos a un perfil bioquímico de sangre, bioimpedancia eléctrica (BIA), absorciometría de rayos X de energía dual (DXA), medidas antropométricas (masa corporal, estatura y pliegues cutáneos de espesor (ST)) y radiografía de mano-muñeca. La evaluación de la composición corporal se realizó por: DXA, ST (ecuaciones Lohman y Slaughter) y BIA (ecuación Houtkooper). El nivel de zinc identificó dos grupos: deportistas normozincémicos e hipozincémicos, determinados por un punto de corte de 11,0 mmol/L. Se observó una diferencia significativa en los datos descriptivos de todos los participantes después de la estratificación del estado de zinc sólo para la concentración de zinc en plasma; se observaron correlaciones significativas entre los métodos de evaluación (porcentaje de grasa: r= 0,34 a 0,98 y p <0,001 a 0,013; masa libre de grasa: r= desde 0,95 hasta 0,9998 y p <0,001), y disminuyeron las correlaciones al estar involucrada la impedancia eléctrica. Los resultados a través de los métodos Bland y Altman mostraron un acuerdo más cercano al comparar DXA y ST. El método ST fue mejor que el BIA para evaluar la composición corporal (en los jugadores jóvenes de fútbol), cuando no estaban disponibles los escaneos DXA. La comparación de los modelos basados en ST mostró que la mejor asociación de valores DXA se obtuvieron para la ecuación Slaughter, seguidos por la ecuación Lohman utilizando la edad ósea en lugar de la edad cronológica. Los niveles de zinc en plasma parecen no influir en la evaluación de la composición corporal, lo que amerita más estudios.

Vitamin D receptor gene FokI polymorphisms influence bone mass in adolescent football (soccer) players.

The genetic influence on bone mineralization during adolescence is unclear possibly due to modifying factors such as skeletal maturation and lifestyle. We evaluated the influence of polymorphisms of the vitamin D receptor (VDR) gene on longitudinal changes in bone mass, bone- and calcium-related hormones in 46 adolescent soccer players (11.8-14.2 years). Total body bone mineral content (TBMC) and density (TBMD) were measured at baseline and after 6 months. Insulin-like growth factor-I (IGF-1), testosterone, intact parathyroid hormone, and activity of plasma bone alkaline phosphatase were measured at baseline and after 3 months. The influence of FokI or TaqI VDR genotypes on changes in the outcome variables were analyzed by univariate ANOVA with adjustment for chronological age, skeletal age and body weight at baseline. At baseline, boys with Ff genotype had higher TBMC, TBMD, TBMD Z-score compared to those with FF genotype (P < 0.05). After 3 months, Ff boys also had higher increment in plasma IGF-1 (P < 0.05). FokI polymorphism did not influence changes in bone mass measurements after 6 months, although differences detected at baseline remained significant after 6 months. There were no differences in the outcome variables according to TaqI genotypes. This study demonstrates that FokI polymorphisms affect bone mass in Brazilian adolescent soccer players and suggests that the FokI effect on bone mineralization occurs during bone maturation, possibly at the initial pubertal stages.

Plasma leptin, plasma zinc, and plasma copper are associated in elite female and male judo athletes.

The purpose of this study was to compare plasma leptin, plasma zinc, and plasma copper levels and their relationship in trained female and male judo athletes (n = 10 women; n = 8 men). Blood samples were obtained 24 h after training to measure plasma zinc, copper, and leptin levels. Subjects presented similar values to age (22 +/- 2 years old), body mass index (24 +/- 1 kg/m(2)), plasma zinc (17.2 +/- 2 micromol/L), copper (12.5 +/- 2 micromol/L), and leptin (5.6 +/- 1.3 microg/L). However, height, total body mass, lean mass, fat mass, and sum of ten-skinfold thickness were higher in male than female. Plasma leptin was associated with sum of ten skinfolds in male (r = 0.91; p < 0.001) and female athletes (r = 0.84; p < 0.003). Plasma zinc was associated with leptin in males (r = 0.82; p < 0.05) while copper was associated with plasma leptin in females (r = 0.66; p < 0.05). Our results suggest that young judo athletes lost sex-related differences in leptin levels. Plasma zinc, plasma copper, and energy homeostasis may be involved in regulation of plasma leptin.

Níveis maturacional e socioeconômico de jovens sambistas do Rio de Janeiro / Socioeconomic and maturational levels of young samba dancers from Rio de Janeiro

Este estudo propõe avaliar o processo de maturação biológica de jovens sambistas, em suas relações com a estratificação socioeconômica, com o crescimento e com a composição corporal, enfatizando o desenvolvimento durante a adolescência, que abrange a passagem da infância à idade adulta, assim como as suas diversas etapas intermediárias medidas através de um conjunto de parâmetros sexuais habitualmente assinalados. Com esse objetivo, foram avaliados a maturação sexual e seus mais importantes sinais físicos e sociais. Foram avaliadas 118 moças entre os 9 e 16 anos participantes da escola de samba Beija-Flor de Nilópolis. Para a determinação de algumas características de desenvolvimento maturacional, foram utilizadas as seguintes medidas: pilosidade axilar, idade da menarca pelos métodos retrospectivo e status quo, pilosidade púbica e desenvolvimento da mama através de auto-avaliação, segundo os critérios de Tanner7. Partindo dos resultados aqui apresentados, parece que: a idade média da menarca é semelhante à encontrada em outras amostras, embora mais baixa; o nível social e o rendimento familiar parecem não interferir no número de sambistas que já passaram pela menarca e na idade média de ocorrência do fenômeno; nos grupos de rendimento socioeconômico mais baixo, são as moças que já vivenciaram a menarca as que apresentam maiores níveis de gordura. Ao contrário, quando o rendimento é superior, são as meninas que ainda não vivenciaram a menarca aquelas que apresentam níveis de gordura mais elevados.