Study design
The present study is characterized as cross-sectional, consisting of four groups. Of these, three were composed of non-conventional professions (models, athletes and ballet dancers) and a control group (university students). All groups were submitted to the same tests (Figure 1).
Subjects
The sample consisted of 41 female teenagers and young adults aged 14 to 24 years who belonged to modeling agencies, sports teams, dance schools and universities from the city of Porto Alegre, Rio Grande do Sul, Brazil. The subjects were allocated according to their daily occupation: models group (MG=11), ballet dancers group (BG=11), athletes group (AG=8) and university students group (UG=11). Modeling agencies, sports clubs and dance schools also signed an assent form. The study was approved by the Research Ethics Committee of the Universidade Federal do Rio Grande do Sul - UFRGS (CAAE: 67847317.5.0000.5347), and was conducted according to the standards proposed by the Helsinki Declaration. The participants and their legal guardians (if participants are under 18 years old) were informed about the experimental protocol and the potential risks, providing written informed consent prior to participation (Figure 1).
Body composition
Height (HEI) and body mass (BM) measurements were carried out. With these values, body mass index (BMI) was calculated (BMI = BM[kg]/HEI2[m]). In addition, bone densitometry (BDM), fat mass, fat-free mass (FFM) and fat percentage (%F) (Lunar Densitometer model DPX.L, "Dual Energy X-ray Absorptiometry") were evaluated in all participants. Data were processed by the system provided for each segment and the BDM results were expressed in g/cm2.
Cardiopulmonary exercise test (CPET)
Peak oxygen consumption (VO2peak) was evaluated by open circuit ergospirometry during a maximum treadmill run test. The highest value reached in the last minute of exercise was used. According to the manufacturer’s instructions, the ergospirometry device (Quark CPET, Cosmed, Italy) was manually calibrated using the known concentrations of gases (21% O2 as reference concentrations, 12% O2 and 5.09% CO2 for calibration). The individuals had the possibility and time to adapt to the treadmill (Quinton Instruments, Seattle, USA) and the ergospirometry device. The participants performed a single progressive maximal exercise test, which consisted of walking for 4 minutes at 4 km.h-1 followed by increases of 1 km.h-1 at each minute until exhaustion. The individuals were verbally encouraged during the test to reach their maximal performance. To verify an exhausting effort, each participant had to meet at least one of the following criteria after the end of the test: 1) VO2 plateau that was defined as an increase in VO2 of less than 2.4 mL.kg-1.min-1 with a corresponding increase in exercise intensity (24,25) 2) obtainment of respiratory exchange ratio (RER) ≥1.0 (26,27) 3) perception of effort greater than 17 (very intense – Borg’s scale of perceived exertion) (28). Heart rate was monitored using a heart rate monitor (FT1–POLAR). In addition, the individuals demonstrated evident signs of extreme physical effort at the end of the test, such as facial flushing, sweating, hyperpnea and unstable gait (26,27). According to these criteria, VO2peak of all participants were considered valid. The ventilatory threshold (VT) and the ventilatory compensation point (VCP) were determined through ventilation (VE), respiratory equivalents (VE/VO2 and VE/VCO2), partial pressure of carbon dioxide on exhalation (PCO2) and partial pressure of oxygen on exhalation (PO2) as a function of oxygen uptake. The criteria to determine VT and VCP were: VT was determined when there was a rapid increase in VE/VO2 and PO2, without a concomitant increase in VE/VCO2 and PCO2; VCP was determined as the point that a rapid increase in VE/VCO2 and a decrease in PCO2 were observed. VT and VCP were associated as the first and second non-linear increase in VE and VCO2 (29,30), respectively. All plots used in the determination of these points used breath by breath gross values. Two independent reviewers blindly determined VT and VCP following the criteria described above.
One-repetition maximum and Muscular Endurance Tests
Maximal strength was obtained by one-repetition maximum (1RM) test for bilateral knee extensors (KE) and bilateral elbow flexors (EF). Bilateral elbow flexion exercise was performed with barbells and dumbbells, whereas bilateral knee flexion exercise was performed in a strength training equipment (Konnen Gym). The subjects were familiarized with all procedures in a single session. On the test day, the participants carried out a warm-up for five minutes in a cycle ergometer, after having performed specific movements for the exercises of the tests. The maximum load of each individual was determined with no more than five attempts with five minutes of recovery between attempts. Performance time for each contraction (concentric and eccentric) was 1.5 seconds controlled by an electronic metronome (Quartz, CA, USA) (31). After the performance of 1RM test, the load corresponding to 60% of 1RM of each individual was fixed. The subjects performed the maximum number of possible repetitions until fatigue. The number of repetitions performed was used as a measure of muscular endurance (ME) (32).
Flexibility
To determine the flexibility of the hip, back and posterior muscles of the lower limbs, the sit and reach test was performed using the Wells bench. The subject remained barefoot, in a sitting position facing the equipment with the soles of the feet flat on the bench, stretched forward along the bench's metric demarcation, with outstretched arms and overlapping hands, seeking the greatest distance in three attempts, maintaining the value reached for 1 second. The highest value achieved was considered as a measure of flexibility (33).
Blood analyses
For the performance of the biochemical analyses of the study, the subjects should be fasting for eight hours. Initially, a 30-minute rest was performed, for further collection of 8ml of a vein in the antecubital region. The samples were stored (vacuitaner tubes with EDTA) and centrifuged (3.500 rpm for 10 minutes), the plasma was aliquoted and frozen (-80º) for further analyses of fasting glucose (FG), fasting insulin (FI), total cholesterol (TC), triglycerides (TG), C-reactive protein (CRP) and high density lipoprotein (HDL). Glucose levels were analyzed by enzymatic colorimetric method (Cobas C111, Roche, Diagnostics, Basel, Switzerland). Low density lipoprotein (LDL) was calculated by Fridewald formula (34) (LDL:TC-HDL-TG/5). Plasma concentrations of FI were evaluated with commercial kits for humans (DRG International, Springfield, USA) by enzyme-linked immunosorbent assay (ELISA) according to the manufacturer’s instructions. For the lipid variables, the Brazilian Guidelines of dyslipidemias and atherosclerosis prevention (35) were used with determined values for TC (<170mg/dL), HDL (>45 mg/dL), LDL (<110mg/dL) and TG (<90mg/dL). Values lower than 100mg/dL and between 1.9 and 23.0µUI/mL were used for FG and FI, respectively (36). For the inflammatory profile, the value of <1mg/L was used (32).
Dietary record
To evaluate dietary consumption and diet quality, a three-day dietary record was applied, describing daily dietary intake with the respective quantities. The record procedure was carried out as follows: each individual recorded all foods and beverages ingested in three days (two typical days and one atypical day of the weekend), also describing the eating schedule, quantities and when possible, the brand of the food. After filling in, all information was checked by a trained researcher, so that there would be no doubt about what was described. The dietary records were further calculated with the DietWin Professional Nutrition Software (Brubins CAS, Brazil).
Depressive Symptoms
Depressive symptoms assessment was carried out through the transcultural and self-applied CES-D depression scale, consisting of 20 statements on a Likert scale with four possible answers corresponding to number 1 (rarely or never – less than 1 day), 2 (few times – 1 to 2 days), 3 (a considerable time – 3 to 4 days) and 4 (all the time – 5 to 7 days). Four items of the instrument are presented with positive sense (blocking the trend to repetitive responses), such items are reversely scored (higher scores indicate greater amount of depressive symptoms). The cutoff score for Brazilian adolescents and young adults is 15, in which individuals with this score or higher are considered at risk for depression (37).
Statistical Analysis
Normality of data distribution was evaluated by Shapiro Wilk test and homogeneity of variables was assessed by Levene test. Mean and standard deviation values were used for descriptive purposes. ANOVA one-way was used to analyze the differences between groups. LSD post hoc was used to establish the location of the differences between groups. Partial eta squared (η2) was calculated as a measure of effect size (ES). Values of 0.01, 0.06 and above 0.15 were considered small, medium and big, respectively (38). Kruskal-Wallis test was applied for the variables that did not present normal distribution. When the Kruskal-Wallis test was significant, pairwise comparisons were performed by Mann-Whitney U test for independent samples. Statistical analyses were performed with SPSS software (version 20.0, SPSS, Inc., IBM Company; NY, USA). The significance level adopted was α<0.05.