Independent Association of Muscular Strength and Carotid Intima-Media Thickness in Children.

The aim of this cross-sectional study was to examine the influence of muscular strength on carotid intima-media thickness (cIMT) in children, controlling for the effect of cardiorespiratory fitness (CRF) and central adiposity and to examine if differences among muscular strength tertiles translate to physiological differences. We assessed cIMT of the common carotid artery in 366 children between 11-12 years of age (191 girls). Measures included cIMT assessed with high-resolution ultrasonography, a maximal handgrip strength test, body fat mass and lean mass from DXA and CRF determined using a maximal cycle ergometer test. Association between muscular strength and cIMT adjusted for CRF and central adiposity, as measured by trunk fat, was tested with multiple linear regression analysis. Differences in risk factors among muscular strength groups were tested with ANOVA. The Muscular Strength Index (MSI) was inversely associated with cIMT independently of CRF and central adiposity (p<0.05). The low MSI group had the highest values of cIMT, waist circumference and systolic blood pressure and the lowest CRF (p<0.05). There was an inverse and independent association between muscular strength and cIMT. Low muscular strength was associated with higher levels of cardiovascular disease risk factors in children.

Effect of a school-based intervention on physical activity and quality of life through serial mediation of social support and exercise motivation: the PESSOA program.

The aim of this study was to explore the effects of social support and behavioral regulation of exercise on physical activity (PA) and quality of life (QoL), in a Portuguese school-based intervention. We hypothesized that serial mediation effects would be present leading to greater levels of PA and QoL. The sample comprised 1042 students (549 boys), aged 10-16 years, BMI = 19.31 ± 3.51, allocated to two groups of schools: control (n = 207) and intervention (n = 835). This study will report the 24 months results of the program, which aimed to develop healthy lifestyles. Questionnaires were used to measure PA, QoL, motivation to exercise and social support. There was no direct impact of the intervention on QoL or PA. Serial mediation analyses were conducted. Social support (P < 0.019) and intrinsic motivation (P = 0.085) increased more on intervention group. Indirect effects were observed in all serial mediation models. The positive indirect effects on PA and QoL were explained by the increase on peer/parent support in serial with the increase in intrinsic motivation (P < 0.01). Parental support led to an increase on external motivation (P < 0.05), which buffered the effects of the intervention. This school-based intervention promoted the development of social support and motivational mechanisms that explained higher levels of PA and QoL.

Increases in intracellular water explain strength and power improvements over a season.

Changes in body components occur over a season, but their impact on performance is still unclear. We aimed to analyze the relationship between changes in leg strength and jump performance with body composition over a season in highly trained athletes. Measures from the beginning to the main competitive periods of a season were obtained in 40 male and 23 female basketball, handball and volleyball players (20±5 years) for fat (FM) and fat-free mass (FFM) estimated by DXA. Total body water (TBW) and extracellular water (ECW) were assessed by deuterium and bromide dilution, respectively, and intracellular water (ICW) was calculated as TBW minus ECW. Maximal strength was determined by the leg press, while jumping height was assessed with squat (SJ) and countermovement (CMJ) jumps. Significant improvements in strength (12.5±20.8%) and jumping height (SJ:8.3±13.9%; CMJ:6.3±8.5%) were found. FFM, TBW and ECW significantly increased (3.0±2.7%; 1.7±5.5%; 3.0±8.6%, respectively), while %FM decreased (-4.5±9.1%) and no changes were observed in ICW (1.2±9.7%). Among body composition changes only ICW was associated with performance even adjusted for gender, age, season length and sport (strength: ß=71.209, p=0.012; SJ: ß=0.311, p=0.049; CMJ: ß=0.366, p=0.018). Body composition, strength and jumping height improved over a season and ICW was the main predictor of performance in national level players.

Association of basketball season with body composition in elite junior players.

AIM: Body composition changes among elite athletes may influence competitive performance. This study aimed to characterize the body composition changes at the molecular, cellular, tissue, and whole-body level of analysis in elite junior basketball players during the course of a season. METHODS: Twelve males and 11 females (16 to 17 years) were evaluated. Dual-energy X-ray absorptiometry (DXA) was used to assess bone mineral (Mo) and lean-soft tissue (LST). Total-body water (TBW) and extracellular water (ECW) were assessed using isotope dilution techniques, and extracellular (ECF) and intracellular fluids (ICF) were calculated. Fat mass (FM) and fat-free mass (FFM) were assessed with a four-compartment model. Body cell mass was calculated (LST - (ECF + ECS)). Skeletal muscle (SM) was estimated using appendicular LST (ALST) as: (1.19 x ALST) - 1.65. At the whole-body level, weight, sum of 7 skinfolds, and muscle circumferences (Mc) were measured. The handgrip and the countermovement jump tests were used for performance assessment. RESULTS: Males increased FFM (4.4±2.3%), TBW (3.5±4.6%), SM (4.5±2.3%), and arm (3.4±2.7%) and thigh (3.8±3%) Mc. Females increased SM (5.9±4.6%) and arm (3.6±3.8%) and thigh (4±5.2%) Mc and decreased ICF (-9.7±13.6%). FFM components differed from the established values based on cadaver analysis. Both genders increased their performance and associations were found between changes in molecular and whole-body components with performance. CONCLUSION: In conclusion the season was associated with an improved body composition profile in males and few changes in females.

Changes in thoracic gas volume with air-displacement plethysmography after a weight loss program in overweight and obese women.

OBJECTIVE: This study was designed to compare measured and predicted thoracic gas volume (V (TG)) after weight loss and to analyze the effect of body composition confounders such as waist circumference (WC) on measured V (TG) changes. DESIGN: Prospective intervention study. SETTING: Outpatient University Laboratory, Lisbon, Portugal. SUBJECTS: Eighty-five overweight and obese women (body mass index = 30.0+/-3.5 kg/m(2); age = 39.0+/-5.7 years) participating in a 16-month university-based weight control program designed to increase physical activity and improve diet. METHODS: Body weight (Wb), body volume (Vb), body density (Db), fat mass (FM), percent fat mass (%FM) and fat-free mass (FFM) were assessed by air-displacement plethysmography (ADP) at baseline and at post-intervention (16 months). The ADP assessment included a protocol to measure V (TG) and a software-based predicted V (TG). Dual-energy X-ray absorptiometry (DXA) (Hologic QDR 1500) was also used to estimate FM, %FM and FFM. Maximal oxygen uptake (VO(2) max) was assessed with a modified Balke cardiopulmonary exercise testing protocol with a breath-by-breath gas analysis. RESULTS: Significant differences between the baseline and post-weight loss intervention were observed for body weight and composition (Vb, Db, %FM, FM and FFM), and measures of V (TG) (measured: Delta=0.2 l, P<0.001; predicted: Delta=0.01 l, P<0.010) variables. Measured V (TG) change was negatively associated with the change in the WC (P=0.008), controlling for VO(2) max and age (P=0.007, P=0.511 and P=0.331). Linear regression analysis results indicated that %FM and FM using the measured and predicted V (TG) explained 72 and 76%, and 86 and 90% respectively, of the variance in %FM and FM changes using dual-energy x-ray absorptiometry. CONCLUSIONS: After weight loss, measured V (TG) increased significantly, which was partially attributed to changes is an indicator of body fat distribution such as WC. Consequently, measured and predicted V (TG) should not be used interchangeably when tracking changes in body composition. The mechanisms relating the reduction of an upper body fat distribution with an increase measured V (TG) are worthy of future investigation.

Body fat measurement in adolescent athletes: multicompartment molecular model comparison.

OBJECTIVE: To assess the accuracy of air displacement plethysmography (ADP) and dual energy X-ray absorptiometry (DXA) per cent body fat (%BF) estimations in comparison with a reference five-compartment (5C) model used as the reference method. DESIGN: Cross-sectional study. SETTING: Outpatient University Laboratory, Lisbon, Portugal. METHODS: A total of 32 girls (age: 15.1+/-0.3 years) and 46 boys (age: 15.3+/-1.2 years) athletes were measured. Body volume was assessed by ADP; bone mineral content was assessed by DXA; and total-body water was assessed by deuterium dilution. Statistical analyses included examination of the coefficient of correlation (r), standard error of estimation (s.e.e.), slope, intercept, and pure error (p.e.) and the agreement between models. RESULTS: For boys and girls, differences between the 5C model and ADP %BF were 0.2 and 1.7% (r = 0.86 and 0.98, s.e.e.= 2.50 and 1.55%, p.e.=2.77 and 2.23%), respectively. Differences between the 5C model and DXA %BF were -1.0 and -3.7% (r = 0.85 and 0.91, s.e.e.= 2.60 and 2.91%, p.e.= 2.90 and 4.66%), for boys and girls, respectively. For girls, regression between ADP and DXA against the reference method did not differ from the line of identity (P > 0.05) while for boys differences were found (P < 0.05). Dual energy X-ray absorptiometry overestimated %BF, particularly in girls. For both genders, large limits of agreement were found between the reference method and both techniques, with the exception of ADP in female athletes. CONCLUSION: We conclude that the two techniques were not precise for individual %BF prediction, though ADP revealed better agreement for girls. However, considering all performance criteria for the mean group, our analysis highlights ADP as a valid and nonbiased tool for the evaluation of body composition in adolescent athletes.

Single and combined effects of body composition phenotypes on carotid intima-media thickness.

BACKGROUND: Central fatness might be a more sensitive predictor of atherosclerotic changes in children than are total body fat measures. However, it is unclear whether a total body fat measure coupled with an estimate of a more central pattern of fat accumulation predicts increased carotid intima-media-thickness (cIMT) better than either measure alone. OBJECTIVE: The objective of the study is to identify the ability of a combination of simple anthropometric screening tools or a combination of objective measures of body composition to predict cIMT. METHODS: cIMT was assessed on the common carotid artery in 349 children aged 11-12 years old (183 girls). Body mass index (BMI), waist circumference (WC) and waist-to-height ratio (WHtR) were dichotomized according to established criteria and indices of total body (TBFI) and abdominal (ABFMI) fat were assessed by dual-energy X-ray absorptiometry and categorized (increased risk ≥85%). Single and combined associations among anthropometric and laboratorial measures with the risk of having increased cIMT (≥85%) and discriminatory performance were tested with logistic regression analysis and Receiver Operator Curve analysis. RESULTS: Children with higher total fatness (BMI and TBFI) or higher central pattern of fat accumulation (WC, WHtR and BFMI) were in higher risk for increased cIMT [odds ratio (OR): 2.08-3.24). The risk for increased cIMT was not higher among children who coupled high total and high central fatness (OR: 2.27-3.10). CONCLUSIONS: Combination of total and central measures of fat does not improve the prediction of increased cIMT in children. Simple surrogate measures of fatness can be used to predict increased cIMT urging special attention to those children who exhibit increased abdominal fat.