Impact of sports participation on components of metabolic syndrome in adolescents: ABCD Growth Study

Objective The objective of this study was to analyze the impact of sports participation (12 months of practice) on components of the metabolic syndrome of both sexes. Methods Observational longitudinal study, party of the study entitled “Analysis of Behaviors of Children During Growth” (ABCD Growth Study), Presidente Prudente, SP. The sample consisted of 171 adolescents [112 boys and 59 girls], the groups were divided between non-sport and sport, according to the inclusion criteria: age 11 to 17 years; absence of known diseases previously diagnosed; no regular use of medications related to blood pressure or lipid metabolism; involvement in sports in the las 12 months (sports group) for at least one year without any regular involvement in sports training routines or physical exercises (non-sports group), signed written consent form parents and adolescents. The high-density cholesterol lipoproteins (HDL-c), triglycerides (TG), and glucose were analyzed by the dry chemical colorimetric method and processed biochemically. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were assessed using an automatic device. Body fat (BF) was estimated using a densitometry scanner. Ethnicity, sex, maturity, and body weight were treated as covariates. Results The adolescents involved in the sport were younger [p-value = 0.001] and with lower PVC [p-value = 0.001] than the non-sport group. The differences () after 12 months were of greater magnitude for the sports group when compared to non-sports group [p-value = 0.013], glucose (moderate magnitude in favor of the sports group; p-value = 0.001), HDL-c (small magnitude in favor of the sports group; p-value = 0.0015) and MetS (moderate magnitude in favor of the sports group; p-value = 0.001). Sport with high cardiorespiratory demand has more pronounced benets than other groups. Sport seems to have a positive relationship in the variables sports participation, weekly volume, and load intensity. Conclusion Sports practice in adolescents had a protective effect on the metabolic components of the metabolic syndrome. HDL-c= high density lipoprotein-cholesterol; MBP= mean blood pressure; MetS= metabolic syndrome. p-value<0.05.


Introduction
Metabolic Syndrome (MetS) is generally de ned by the cluster of cardiovascular risk factors, with three or more markers such as obesity, high blood pressure (HBP), dyslipidemia [increase in triglycerides (TG) and decrease in high-density lipoprotein (HDL)] [1][2][3][4]. It is estimated that a total of 34.2% of North Americans have MetS, with 20.2% in young adult men and 16.7% in women [5]. The prevalence of MetS in children and adolescents is about 2% depending on the adopted criteria, also, the prevalence of MetS in the pediatric population has been increasing in parallel with the obesity epidemic [6].
According to the World Health Organization (WHO), obesity is de ned as the accumulation of abnormal or excessive fat that poses a health risk [7]. Obesity is present in about 34.8% of men and 36.5% of North American women aged 20 to 39 years [8]. In adolescents, obesity affects about 20.6% (obesity -BMI at or above the sexspeci c 95 th percentile) and 9.1% (extreme obesity -BMI at or above 120% of the sex-speci c 95 th percentile) [9]. The prevalence of blood pressure in children and adolescents (8 to 17 years) affects about 1.6%, dyslipidemia affects about 20.2%, while the prevalence of type II diabetes (T2DM) affects about 0.46% [10,11].
MetS are directly related to increased sedentary behavior and low levels of physical activity [12]. Physical activity is considered a modi able factor in lifestyle capable of promoting the prevention and treatment of cardiovascular and metabolic diseases [13]. According to WHO and The US Preventive Services Task Force (USPSTF), they found evidences which supported that moderate-to-vigorous physical activity (MVPA) accumulated at least 60 minutes is effective to promote improvements -in a short-term (up to 12 months) -on weight status [14,15]. A 2015 review found positive adaptations to childhood obesity, mainly acting to restore cellular and cardiovascular homeostasis, to improve body composition, and to activate metabolism by any type of physical exercise, [16] following the guidelines outlined by the 2011 National Heart, Lung, and Blood Institute (NHLBI) Expert Panel on Integrated Guidelines for Cardiovascular Health and Risk Reduction in Children and Adolescents and more recent studies involving metabolic syndrome in the pediatric population [14,17,18].
Physical activity and MetS have opposite effects, physical activity can promote adaptations in the cardiovascular and metabolic components in adolescents [19,20]. Sports practice is the main manifestation of being from the subdomain of physical activity, becoming the main responsible for the adolescents to reach the levels of MVPA [21,22]. This sports practice is often carried out at school [23] or by municipal projects. Each sport has different cardiorespiratory demands: High (>6 METs) and Low (<6 METs), being responsible for determining energy expenditure during the activity [24]. Therefore, our hypothesis of sports practice would be able to promote adaptations in lipid metabolism and the cardiovascular system of adolescents, regardless of cardiorespiratory demand. Thereby, this study aimed to analyze the impact of 1-year sports participation on components of metabolic syndrome in adolescents of both sexes.

Sampling
This study is part of longitudinal research entitled Analysis of Behaviors of Children During Growth (ABCD -Growth Study). This is an on-going study designed to identify the impact of sports participation on different health aspects among adolescents, including metabolic syndrome components. The study is being carried out in the city of Presidente Prudente (200,000 inhabitants and human development index of 0.806, the western state of Sao Paulo, Brazil). Researchers and staff members of the Laboratory of InVestigation in Exercise (LIVE) (Sao Paulo State University -UNESP) were responsible for the 2017 baseline and follow-up data collection. The ethics committee of the UNESP campus of Presidente Prudente approved the study (process number 1.677.938/2016). All parents, coaches, and adolescents signed a written consent form.
The sampling process has been described elsewhere [25][26][27]. Brie y, after authorization of local authorities, school units and sports clubs were contacted to explain the research aims and methods of the ABCD -Growth Study. In the eleven facilities (spread out in the metropolitan area of the city) that were accepted to host the research, adolescents and their parents/legal guardians were contacted, and written consent forms were delivered. The only adolescent who ful lls all inclusion criteria were measured/interviewed: (i) aged between 11 and 18 years; (ii) absence of any known diseases previously diagnosed; (iii) no regular medicine use related to blood pressure or lipid metabolism; (iv) if athletes, at least one year of training experience; if control group (schoolchildren), at least one year without any regular engagement in organized sports or physical exercise routines; (v) written parental consent and adolescents' assent, both signed.
At baseline, 285 adolescents agreed to participate and take part in the baseline data collection. Twenty-six adolescents had any missing data at baseline and were excluded from this manuscript (n= 259). Moreover, after to participate in data collection, or gave up participating (n= 184). Additionally, 13 adolescents were excluded due to any missing in the components of MetS on follow-up data collection. This sample size of 171 participants allowed the statistical power (80%) to detect signi cant (Z= 1.96) coe cients of correlation (standardized score [r]) ≥0.213 in our statistical analysis.  [29]. Measurements were performed after 10 minutes at rest and three measurements were obtained with an interval of one minute between them and the mean of the three measurements was considered [30].  Coaches keep contact with researchers during the entire follow-up period and only adolescents who frequently participated in the training sections were reassessed in the follow-up moment. At baseline, it was reported the previous time of engagement in the current sport (in months), the number of days/week training, time spent in the exercise sections (in minutes). Therefore, it also calculated the overall time per week of training (minutes/week).
Additionally, two non-consecutive training sections in the same week were entirely monitored by the researchers. Heart rate (HR) was monitored during the training sections using a Polar V800 HR monitor (a plastic strap was placed on the trunk to measure HR via telemetry [Polar Electro®, Finland]) and the average values of the two sections were adopted [32]. The average percentage of maximum HR reached during the two sections has been multiplied by the number of training per week of each athlete in order to create a proxy of training load. [elevated] [35]. The relationship between parameters of sports participation and changes on MetS components was assessed using partial correlation, adjusting by sex, ethnicity, PHV (baseline), and body fatness (baseline).

Results
The adolescents in the sports group were younger (p-value = 0.001) and with lower PVC (p-value = 0.001) than the adolescents in the non-sports group. In the parameters of body fat, no signi cant difference was found between the groups. In the MetS components at baseline, the group of young sportspeople had higher values for glucose (p-value = 0.001) compared to the non-sports group, while the group of young sportspeople had lower values for depression (p-value = 0.010) compared to the non-sports group (Table 1).  Table 2 compares the changes that occurred after 12 months of follow-up between the two formed groups. In the unadjusted analysis, there were differences for the variables TG (p-value = 0.003), HDL (p-value = 0.025), blood glucose (p-value = 0.001) and Z MetS score (p-value = 0.001).
In adjusted analyzes, changes over the follow-up differed between the sports and non-sports groups for TG  Changes in HDL-c concentrations were positively related to the previous time of sports participation, weekly volume, and training load (low magnitude, ranging from 0.158 to 0.163). Fasting blood glucose (low magnitude, ranging from -0.383 to -0.157) and the Z MetS score (low magnitude, ranging from -0.298 to -0.186) were inversely related to all variables analyzed (Table 3).  When sports cardiorespiratory demand (low and high) was considered, the mean values of the Z MetS score were negative, and the non-sports group showed positive values (Figure 1).

Discussion
Our main ndings highlight that adolescents engaged in sports practice showed a decrease in risk factors for metabolic syndrome (especially metabolic ones), regardless of body adiposity.
In our sample, at the baseline of the study, most of the adolescents analyzed did not present changes in the metabolic and cardiovascular components considered. Perhaps therefore blood pressure values have not changed signi cantly. Although reports point to a negative relationship between sports and blood pressure [36,37] and greater parasympathetic activity among adolescents engaged in sports activities [38,39], it must be considered that the hypotensive effect of physical exercise on non-obese adolescents is still an unclear aspect in the pediatric literature [40,41]. Another confounding component in this theme is the fact that blood pressure naturally changes throughout the human growth phase [42]. In this sense, although sports practice in adolescence seems capable of preventing high blood pressure in adulthood [43], further studies are needed to clarify how this relationship behaves during human growth stages.
Unlike the ndings for blood pressure, the concentrations of TG, HDL-c, and glucose seemed more susceptible to changes throughout the follow-up (reductions in TG and glucose and increases in HDL-c). On the other hand, although the literature points out that different types of exercise can affect the lipid and glycemic pro le in adults [44][45][46], these ndings are less clear among pediatric groups. Furthermore, the literature has pointed out that the regular practice of physical exercises can affect the components of the lipid pro le of obese adolescents, whereas this effect does not seem to be so clear among young people with normal values of body fat [47]. Our ndings become more interesting, because (i) it involves sports practice (the main manifestation of physical exercise in adolescence, but little explored in the literature) and (ii) our sample was composed of predominantly non-obese adolescents and with few changes in the components of cardiovascular and metabolic factors considered. Perhaps, for this reason, our ndings were, for the most part, of low magnitude.
Another aspect that draws attention is the fact that these changes were observed even in a scenario in which body adiposity remained stable. A hypothesis formulated to support the relationship between physical exercise and lipid pro le would be the fact that physical exercise induces changes in the components of the lipid pro le through increases in Apolipoprotein A1 (APOA1) [48,49], which are not exclusively dependent on changes in adiposity [50]. Also, aspects that indicate a longer previous engagement time and the weekly volume of sports practice seem more relevant than the daily time of sports practice.
The lowest values observed in the sports group for the Z MetS score re ect the aggregate effect on metabolic components, but not cardiovascular and adiposity. Although recreational activities can generate bene ts for obese and less active adolescents [51,52], among these young athletes the greater cardiorespiratory demand of some sports activities (intensity indicator) promoted improvements in metabolic aspects [53]. These ndings corroborate with some reports in the literature, which highlight the importance of adequately controlling the training load [54].
Our study has some limitations, which need to be recognized. Thus, the lack of control of food consumption (a factor that directly affects biochemical tests) is a relevant limitation in this research. Furthermore, the absence of a more in-depth follow-up on the different competitive calendars of these teenagers also needs to be highlighted.
We conclude that adolescents who practice sports, regardless of body adiposity, have a protective factor in the components of metabolic syndrome.

Declarations
Ethics approval and consent to participate

Consent for publication
Not applicable.

Methods
The methods of study were carried out in accordance with relevant guidelines and regulations including the Declaration of Helsinki for human studies by the World Medical Association.

Availability of data and materials
The datasets generated and/or analyzed during the current study are not publicly available due it contains private information from medical records but are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests. Author's contributions VAM participated in the conception, analysis, interpretation of data, and writing of the article; WT was involved in data collection, revision, and relevant contributions of the text; EDLM was involved in data collection, revision, and relevant contributions of the text; LGMC was involved in data collection, review and relevant contributions to the text; AEvHM was involved in the revision and relevant contributions of the text; JBU was involved in data collection, revision and relevant contributions of the text, AAAJ was involved in the interpretation of data, revision and relevant contributions of the text; DGDC was involved in the interpretation of the data, revision and relevant contributions of the text; RAF was involved in the interpretation of the data, statistical treatment, revision and relevant contributions of the text. All authors read and approved the manuscript. Figure 1 Z MetS score of the groups to the cardiorespiratory demands of sports practice among adolescents.