2.3. Data Collection
Data were collected in February 2016 by five physical education teachers and three cardiologists, who were previously trained and supervised by the project´s coordinator. Data were collected at the school (anthropometric, hemodynamic measurements, lipid and glucose profile, cardiorespiratory fitness, physical activity, and SB) and the clinic of cardiology (left ventricular mass), during the weekend, in moments previously scheduled with the parents and the school board.
Body mass (kg), body height (cm), and waist circumference (WC; cm) measurements were assessed following WHO standardization [
17]. Body mass was measured using a Welmy® digital scale with 100g accuracy. To measure body height, a stadiometer attached to the scale was used. The vertex and the plantar region of the children were used as reference points, and body mass index (BMI) was calculated. Children who presented BMI above the 85th percentile for age and sex were considered overweight [
17]. In all measurements, children were standing bare feet and wearing light clothes.
WC was assessed at the midline between the lower edge of the rib cage and the upper limit of the iliac crest and was measured with Sanny® metal tape measuring 1mm [
17].
The sum of skinfolds (triceps and subscapular skinfolds) was performed according to the standardization protocol proposed by Harrison et al. [
18], using a Lange® skinfold caliper.
All anthropometric measurements were performed in triplicate, by the same evaluator. For analysis, the mean value was adopted.
Systemic blood pressure was measured by a single evaluator, using a digital automatic device (Omron®); this equipment has good levels of sensitivity and specificity for blood pressure measurements in children and adolescents [
19]. Three measurements were performed, with a five-minute interval, according to the Brazilian Society of Cardiology [
20], and the median value was used for analysis. This procedure has already been adopted in previous studies [
21]. Mean blood pressure (MBP) was considered for the analysis, the same was calculated by [(2 x diastolic blood pressure) + systolic blood pressure)/3].
For biochemical profile measurements, 10 ml of venous blood were collected from the antecubital vein after 12 hours of fasting. The blood sample was deposited in a vacuum tube with separating gel and without anticoagulant and was stored in thermal boxes for later analysis in a specialized laboratory. Triglycerides (TG), total cholesterol (TC), low-density cholesterol (LDL-C), high-density cholesterol (HDL-C), and glucose levels were determined in mg/dl [
22].
Cardiorespiratory fitness (CRF) was verified through the 6-minute running and walking test proposed by Gaya et al [
23]. The test was conducted on the school court and was performed individually. The test was guided by a Physical Education teacher, who monitored the time and verified the distance reached by the child during the given time. During the test, motivational words were directed to the children.
Left ventricular end-diastolic and end-systolic measurements were obtained with the patient in a partial left lateral position according to recommendations by the American Society of Echocardiography [
24]. Frames with optimal visualization of interfaces and showing simultaneous visualization of the septum, left ventricular internal diameter, and posterior wall were used. A Level 3 echocardiographer performed the interpretations. Left ventricular mass was calculated by using the Devereux formula: left ventricular mass (g) = 0.80 × + 0.6 g. The left ventricular mass was indexed according to body surface area.
The voltage based on the Sokolow-Lyon criteria has been used to diagnose left ventricular hypertrophy and has been associated with the presence of cardiovascular disease [
25]. Individual leads were analyzed by measuring the tallest R or R′ and the deepest S or QS complex in all the precordial and using the PR segment as baseline. In cases of voltage differences within the same lead, only the largest complex was selected. The proposed criteria were obtained by adding SD to the in V4 (SD + SV4). The Sokolow-Lyon voltage was obtained by adding the amplitude of S in V1 and the amplitude of R in V5 or V6 ≥3.5 mV (SV1 + RV5 or RV6); the limb lead voltage criteria amplitude of R in aVL >1.1 mV (RaVL) and amplitude of R in L1 >1.4 mV (RL1).
PA and SB were objectively measured using accelerometry (GT3X+, ActiGraph®, USA). Children were instructed to use the accelerometer affixed to the waist during eight consecutive days and remove for fighting and water activities, and at night.
Data were collected at a sampling rate of 80 Hz and epochs of 15 seconds. To reduce the data, the ActiLife 6.12 software was used, and data validity was set adopting the following criteria: three weekdays, and one weekend day; at least 10 hours/day of registered data (06: 00h to 00: 00h); 10 or more consecutive minutes of zero counts were established as non-wear time [
26]. The time spent in SB and MVPA were obtained by the weighted average of minutes/day, using established cut-off points proposed by Evenson et al. [
27].
To characterize the sample, a Student T-test was used to compare the means of all variables between boys and girls.
A network analysis was conducted to assess the associations between MVPA, SB, and cardiovascular risk factors. The “Fruchterman-Reingold” algorithm was applied, and data were shown in a relative space in which variables with strong permanent statistics are together, and with weak applied variations repelled one another [
28]. The least absolute contraction and selection operator was used to obtain regularization and to obtain a less sparse model [
29]. The partial correlation parameter was adjusted to 0.25 to create a network with greater parsimony and specificity [
30]. Additionally, a 1.000-bootstrap resampling was performed.
Three centrality indicators were used to determine the role of each variable in the emerged network: (1) betweenness (centrality between the parts), estimated from the number of times that a node is part of the shortest path among all the others pairs of nodes connected to the network; (2) closeness, which is determined from the inverse of the distances from one node to all others; and (3) strength (degree/centrality), which is the sum of all the weights of the paths that connect a node to the others [
31]. The Jasp software version 0.12 was used.