INTRODUCTION

Functional capacity (FC) is the ability that an individual has to autonomously perform activities of daily living (ADLs) ¹ . It has the following components: absolute cardiorespiratory fitness (VO ₂ max) (L.min-1) and fitness relative to body mass (mL. kg-1.min-1). A sedentary lifestyle associated with low levels of cardiorespiratory fitness explains the increase in childhood and adolescent obesity ² . In addition, there is an association between cardiorespiratory inability and cardiovascular risk factors, and it can be used to compare the physical fitness of adolescents with different nutritional statuses ^2,3 .

For this reason, the appropriate use of the components of cardiorespiratory fitness, resistance and body composition, with the practice of physical activity in childhood and adolescence, brings several health benefits ^3,4 . On the other hand, low levels of regular cardiorespiratory activity favor the development of numerous chronic degenerative disorders, such as obesity, cardiovascular diseases and high blood pressure, at increasingly early ages ^4,5 .

The Ministry of Health recently published data revealing the increase in obesity in Brazil ⁶ . According to the survey, the prevalence of the disease increased from 11.8% in 2006 to 18.9% in 2016, with 53.2 thousand people being overweight. Estimates for Latin America are that 3.8 million children and 21.1 million adolescents are overweight or obese ⁷ . Given this scenario, the World Health Organization (WHO) included physical activity in the Global Public Health Agenda by launching the Global Strategy on Diet, Physical Activity and Health, with the aim of reducing physical inactivity by 10% by 2025 ⁷ .

The assessment of FC or cardiorespiratory fitness can be simulated through physical tests, as they allow the diagnosis of possible alterations, as well as the evaluation of the effect of interventions based on exercise programs ² . The six-minute walk test (6MWT) assesses FC during physical exercise, in addition to being widely applicable, low-cost and easy to administer ^8,9 . The test can also assess the responses of the systems involved during exercise, including the cardiorespiratory and musculoskeletal systems ⁹ . In this context, the objective of the present study was to analyze the influence of anthropometric parameters on the functional walking capacity of adolescents from a public school in Goiânia, Goiás.

MATERIALS AND METHODS

A cross-sectional study was conducted with 93 students; however, at the end of the study, only 85 adolescents participated in all stages of the research. Of the 85 participants, 55 were female and 30 were male, aged between 11 and 14 years old, and were regularly enrolled at Colégio de Aplicação do Instituto de Educação de Goiás (IEG), a public school in the city of Goiânia, State of Goiás. Data collection was carried out between August 2015 and March 2016. The G Power 3.1.9.2 software (effect size of 0.60, power of 0.80 and error of 5%) was used to calculate the sample, resulting in 85 participants. The participants were divided into two groups (eutrophic and overweight/obese) according to the physical evaluation after admission to the research.

This study was developed in accordance with the Guidelines and Standards for Research Involving Human Subjects (Resolution 466/2012, of the National Health Council), and approved by the Research Ethics Committee of the Pontifical Catholic University of Goiás – PUC/GOIÁS (CAAE 14954913.6.0000.0037). All participants received an invitation containing the study procedures and the Free and Informed Consent Form (FICF) (Appendix 1). Upon returning with the FICF completed and signed by their parents or guardians, data collection began. The inclusion criteria for the study were: age range of 11 to 14 years, of both sexes, whose parents and/or guardians authorized legal participation through the FICF, and being regularly enrolled in the school system. The exclusion criteria were: adolescents with orthopedic deficits, unstable angina and myocardial infarction during the months prior to the test and who were not properly medicated, resting heart rate (HR) greater than 120 beats per minute, systolic pressure greater than 180 mmHg and diastolic pressure greater than 100 mmHg, pulmonary embolism, need for walking assistance, significant visual, auditory or cognitive alterations that prevented participation in the test, adolescents classified as underweight and adolescents who refused to participate in the study or whose parents did not provide legal consent through the TCLE.

Body weight (kg) was measured using a digital scale (Filizola ^® , series 3134 no. 86713 with 100 g divisions and a maximum load of 150 kg), where the adolescents were barefoot, wearing light clothing, and in an orthostatic position, with their feet apart and looking fixedly at a point ahead. Height (cm) was measured using a stadiometer with a fixed base and a movable cursor, with the adolescent in the orthostatic position and with their feet together. To ensure the accuracy of the height measurement, a set square was used resting on the vertex of the head.

The body mass index (BMI) (kg/m²) was calculated according to reference data from the World Health Organization (WHO) ¹⁰ . For the nutritional classification of percentiles, the technical standard of the MedCalc system was used, where adolescents were classified as: Eutrophic when the BMI/age was between the 10th and 85th percentile; Overweight when the percentile was above or equal to 85; Obesity with a percentile above 97. Adolescents classified as underweight were excluded from the study due to the small number in the sample (n = 2). Those classified as overweight and obese were allocated to the group called Excess weight in this study.

Sexual maturation was measured by self-assessment using figures proposed by Tanner (1981). Figures with different levels of pubic hair development and breast development for girls and figures on the genitalia for boys. The adolescents marked the figures corresponding to their pubertal stages and from this they were classified as prepubertal (stage 1 in the breasts and pubic hair in girls; stage 1 in the genitalia and pubic hair in boys) and pubertal (stage ≥2), with prepubertal individuals not included in the study.

The abdominal circumference (AC) was determined during normal expiration with a non-stretchable tape with resolution in millimeters (mm) and length of 2 meters. This was obtained at the level of the umbilical scar, with the adolescent in the vertical position and the abdomen relaxed. The measurement of the neck circumference (NC) was performed with the adolescent standing and the head positioned in the horizontal plane. The neck was palpated to locate the cricoid cartilage, where the tape measure was positioned, exerting minimal pressure. The thickness of the triceps, calf and subscapular skinfolds was measured using a scientific adipometer (Cescorf ^® ) with a resolution of 0.1 mm, according to the (ISAK) procedures ¹¹ .

The socioeconomic status was assessed using a questionnaire developed by the Brazilian Association of Research Companies (ABEP). The calculation was made using a point system adopted as the Standard Criteria for Economic Classification in Brazil. The total score ranged from 0 to 46 and was classified as follows: class A=35-46; B=23-34; C=14-22, D=8-13 and E=≤7. The adolescents responded about transportation to school, activities practiced, TV time, quality and quantity of sleep, health perception and diet and physical activity practice ¹² . Sedentary behavior was assessed using the Socioeconomic Physical Activity Questionnaire, validated in the Brazilian population.

Functional capacity was assessed using the 6MWT. The individuals were previously assessed and a physical examination was performed during this assessment. The participants underwent the 6MWT following the general criteria standardized by the American Thoracic Society (ATS) ¹³ , i.e., a 10-minute rest period in the pre-test period with initial and final measurements of blood pressure and subjective sensation of exertion using the Borg Scale (Appendix 5), heart rate (HR), respiratory rate (RR) and peripheral oxygen saturation (SpO ₂ ). The reference values ​​used were in accordance with the reference equations for predicting the distance in the 6MWT proposed according to the classification for Brazilians ¹⁴ .

Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS) statistical program, version 23.0. Data normality was verified using the Kolmogorov-Smirnov test . The descriptive statistical analysis of the data was processed using mean and standard deviation for continuous variables and calculation of frequency and percentage for discrete or categorical variables. The statistical procedures used were Student ‘s t-test for independent groups (comparison of eutrophic and overweight/obese groups), for anthropometric and cardiorespiratory parameters of the 6MWT, Fisher’s exact test to compare frequencies between sex, sexual maturation and physical activity and, finally, Pearson ‘s correlation test to correlate the different anthropometric variables with the parameters of the functional capacity of the adolescents. In all tests, a significance level of 5% (p ≤ 0.05) was considered.

RESULTS

This study considered a sample composed of 85 adolescents, 64.7% of whom were female, with ages ranging from 11 to 14 years (mean of 12.4 years). Regarding age, the students were categorized as 11 years old (n = 18); 12 years (n= 30); 13 years (n= 22); 14 years (n= 15), with 72% classified as eutrophic and 28% as overweight.

Table 1 presents the characteristics of the adolescents regarding sex, sexual maturation and physical activity. There were no statistically significant differences between the groups stratified by BMI. Table 2 showed significant differences between the groups regarding body weight, WC, CC, BMI and skin folds, with the exception of the height variable. On average, the overweight group presented high values ​​of anthropometric parameters and body composition when compared to the eutrophic group.

No significant differences were identified between HR and DBP before the 6MWT, nor DBP, HR and SpO ₂ after the 6MWT. Significant differences (p ≤ 0.05) were observed between the variables of SBP, RR and SpO ₂ before the test and SBP and RR after the walking test. The mean of the overweight group was higher than that of the eutrophic group, indicating that overweight and obese adolescents suffered greater cardiorespiratory repercussions before and after the walking test

(Table 3). In general, eutrophic individuals presented better cardiorespiratory fitness. There was no significant difference between the groups in the mean distance walked (SD). Although the values ​​presented in the table were not significant (p ≤ 0.05), the adolescents were walking within the expected mean for this population during the 6MWT.

Table 4 presents the results of the analysis of correlations between anthropometric variables and cardiorespiratory fitness parameters before and after the walking test. In general, although significant, the correlations were considered weak (correlation coefficient r ≤ 0.05). It was found that there was a correlation between BMI and SBP, RR and SpO ₂ before the test and SBP after the walking test. WC showed a correlation with SBP before and SBP and DBP after the test. Evaluating the increased value of CP, it was also found that there was a correlation with SBP, DBP and SpO ₂ before and SBP after the test. In the evaluation of DCT, there was a significant positive correlation with the increase in SBP, RR and SpO ₂ before the test, and BP and HR after the test. DCS with SBP before the test and SBP, HR and RR after the test and, finally, DCP correlated with HR and RR after the walking test. These results explain the negative impact of high anthropometric parameters on cardiorespiratory fitness and, as a consequence, an unsatisfactory functional capacity during the test.

DISCUSSION

The purpose of this study was to verify the association of anthropometric parameters with cardiorespiratory fitness of adolescents through the 6MWT. The test proved to be reproducible in healthy adolescents, although the performance of both groups was similar in relation to DP. This corroborates another study already conducted in Brazil ¹⁴ , which evaluated the applicability of the test to estimate the distance to be walked in the Brazilian population ¹⁴ . This study also found no significant difference in DP, demonstrating that test performance and cardiorespiratory fitness did not interfere in the distance walked due to changes in energy expenditure ¹⁴ .

A study conducted at the Elderly Health Care Center (CASI) in Piripiri (PI) also found an association with high body mass index and low functional capacity performance of individuals in different age groups during the 6MWT¹. In this study, 70% of the participants were hypertensive and 62.5% were diabetic, and the participants were walking within the average predicted in the literature ^{1, 14} . The average SD of the elderly participants was similar to that of the present study, despite the differences relative to the population included. This justification can be understood by factors that can influence the performance of adolescents in the 6MWT, among them, puberty and growth spurt, due to the great influence of stride length and speed on the SD in the test ^15,16 . Aspects inherent to school age related to learning difficulties, interest and motivation during the test, through encouraging phrases at different periods of time, also need to be considered in the results.

The present study revealed a worrying fact that 28% of the adolescents were classified as overweight/obese. The obesity observed in the present study showed a prevalence similar to that observed in the city of Florianópolis (SC), where children aged seven to 14 years from public schools were analyzed. In this study, it was observed that approximately 23% of the young people were overweight or obese and had a predisposition to risk factors for metabolic and cardiovascular diseases and their relationship with poor performance in the 6MWT ¹⁶ . Another study analyzed 29 healthy Brazilian children aged between six and 14 years and verified the reproducibility of the 6MWT in this group, where similarity was observed in the behavior of the physiological parameters and in the mean SD during the test ⁹ .

The adolescents analyzed showed higher body weight according to BMI, higher NC, higher skinfold thickness, and sedentary behavior. These findings corroborate the results of a study conducted in Paraná, which assessed schoolchildren aged between seven and ten years and identified health risks due to overweight ⁴ . Another study observed a higher percentage of obese individuals aged between nine and ten in public schools ¹⁵ . A similar study conducted with children aged seven to ten in Florianópolis used the sum of four skinfold thicknesses and found that BMI had better diagnostic performance in screening for excess body fat ¹⁶ . These authors indicated a significant association between low cardiorespiratory fitness and high adiposity, regardless of the sex of the adolescents analyzed.

NC can be added to the nutritional assessment, being an anthropometric measurement that allows the identification of overweight and obesity in children and adolescents ¹⁷ . Considering the present results, there was an association between NC and SBP before and after the 6MWT, which indicates that NC is also established as an indicator of adiposity in Brazilian adolescents and that changes may negatively impact blood pressure, and may be used as an indicator of metabolic syndromes. This finding is in agreement with a study carried out in Northeastern Brazil, where 1,474 adolescents were evaluated and NC showed a significant correlation with systolic blood pressure ¹⁷ . Few pediatric studies have explored NC and the mechanisms involved to justify the association with cardiometabolic risk factors.

In this study, the subscapular skinfold was used as central adiposity and the triceps skinfold (TSF) as peripheral adiposity. TSF showed a correlation with the cardiorespiratory parameters of SBP and HR post-test. This finding may be influenced by the low level of physical activity or be attributed to the stage of sexual maturation, since fat deposition begins with greater emphasis at the beginning of puberty ¹⁸ . These results agree with the study carried out in Pelotas (RS), in which the percentage of DCT was high by 20.2% in both sexes and was associated with high BMI, also associated with puberty and low level of physical activity ¹⁹ .

Regarding the differences in cardiovascular responses, adolescents presented greater cardiorespiratory demand during the 6MWT, which revealed higher values ​​of HR, blood pressure and SpO ₂ . This increase observed in the pediatric population may be compensatory for a smaller cardiac volume and lower systolic volume³. Although the O _{2 pulse}is only an indirect estimate of systolic volume, it is suggested that this finding may be related to lower systolic volume and lower venous return³. In addition, the present study revealed high RR values, which demonstrates that the ventilatory pattern in the pediatric population depends on the maturational pattern. Within the same context, a study indicated that cardiorespiratory and metabolic responses during the progressive exercise test are different in children compared to adults. These differences may suggest that children have lower cardiovascular and respiratory efficiency³.

Using questionnaires to assess the level of physical activity, we observed that only 29% of the students performed extracurricular physical activity. The practice of physical activity is an important component for greater daily energy expenditure ⁶ . This corroborates other studies already conducted with adolescents in Brazil ¹⁵ and other countries such as Portugal ⁸ , where there was also an association between cardiorespiratory resistance and a higher percentage of acquiring comorbidities related to physical inactivity and, consequently, low functional capacity ²⁰ .

Obesity has a multifactorial etiology with hereditary, environmental, behavioral, cultural and socioeconomic determinants that interact and enhance each other ²⁰ . Other changes at the psychosocial level also reduce quality of life and increase the number of inadequate responses ⁴ . Identity and self-image disorders associated with low self-esteem are also significant in obese children and adolescents, who are victims of both external prejudices and their own prejudice. Situations involving physical activities or relationships with other individuals may represent a reason for social avoidance for them, which may contribute to triggering behaviors associated with social phobia or even symptoms that fit the diagnosis of depression ²⁰ .

Based on the results found, it was found that the present study contributes to the literature regarding the detection of childhood and adolescent obesity and preventive assessments of health risks for Brazilian schoolchildren. It is also important to emphasize that the results are applicable to the sample studied, and that generalizations are limited due to the sample size. Furthermore, other functional capacity parameters were not assessed in the current study, such as running ability, standing up from the floor or expirometric assessments to test exercise tolerance. These parameters can be investigated in future studies on the same topic.

Finally, the study confirmed the need for health promotion actions in schools, showing the importance of including physical activity and its influence on the cardiorespiratory component during childhood and adolescence during the school period.

CONCLUSION

Based on the study, it is concluded that anthropometric parameters influenced functional capacity. There was no impact of excess weight on the functional walking capacity of adolescents, since both groups walked similar values ​​in the PD. It is believed that high anthropometric parameters of BMI, abdominal circumference, neck circumference and triceps skinfold are associated with a negative impact on the cardiorespiratory capacity of adolescents before and after the walking test.