Effect of concurrent training on gender-specific biochemical variables and adiposity in obese adolescents

Objective: The purpose of the present study was to analyze the effects of a 20-week concurrent training (20 WCT) intervention program on gender-specific body composition and metabolic variables in obese adolescents. Subjects and methods: Sample was composed of twenty-five obese adolescents, aged between 12 and 15 (13.4 ± 0.96) years. Fat-free mass (FFM), percentage trunk fat mass (TFM%) and percentage fat mass (%FM) were evaluated through dual-energy X-ray absorptiometry (DXA). Measurement of intra-abdominal adiposity (IAAT) was performed using ultrasound. Blood pressure was measured and blood samples analyzed for total cholesterol (TC), high-density lipoprotein cholesterol (HDL-c), low-density lipoprotein cholesterol (LDL-c), triglycerides (TG) and plasma glucose. All participants performed the concurrent training (combination of weight training and aerobic training) three times per week, one hour per day, for 20 weeks. Descriptive analysis and analysis of variance (ANOVA) for repeated measures were used to compare baseline, 10 week and 20 week moments using the Bonferroni post-hoc test. Statistical significance was set at p < 0.05. Significant decrease in TC, LDLc and TFM% were verified in both genders after the 10 initial weeks of concurrent training. Results: A significant increase in height was found in both the male and female groups (p = 0.001 and p = 0.047, respectively), after 20 weeks of concurrent training. In addition, several modifications were observed in body composition and metabolic variables, with a significant decrease in BMI (p = 0.002 and p = 0.017), BMI z-score (p = 0.033 and p = 0.004), FM% (p = 0.002 and p = 0.002), TFM% (p = 0.009 and p = 0.018), TC (p = 0.042 and p = 0.001) and LDL-c (p = 0.006 and p = 0.001) in the male and female groups, respectively, after 20 weeks of intervention when compared with baseline. Conclusion: Our results identified that concurrent training was an effective intervention for treating metabolic variable and body composition disorders, in both genders, by decreasing adiposity with consequent improvement in BMI and BMI z-scores, and enhancement in lipid profile variables. Arch Endocrinol Metab. 2015;59(4):303-9


INTRODUCTION
E pidemiological evidence indicates obesity as a re levant concern in the pediatric population (1,2). It is well documented that obesity constitutes a risk factor for other chronic outcomes, such as insulin resistance (3), elevated blood pressure (4), dyslipidemia (5) and non alcoholic fatty liver disease (6). Moreover, obesity trig gered in childhood tends to continue into adulthood (7).
The specificity of the distribution and accumulation of adiposity varies according to gender. Females present a higher concentration of adipose tissue in the subcutaneous gluteofemoral region and males a higher concentration of fat mass in the abdominal region. These differences are due to the influence of hormones such as estrogen, testosterone, cortisol and growth hormone (8).
Independent of age, physical exercise and dietary control are widely prescribed to treat obesity (9,10). In addition, there are a wide variety of exercise pro tocols targeting weight loss, although their effective ness is not clear when applied to pediatric population. Aerobic and strength exercises have been used to re duce fat mass and improve fasting glucose and lipid metabolism (11,12) however, despite the effect of both methods on weight loss programs, there is not sufficient evidence that strength training (ST) pro motes significant improvements in the metabolic pro file (13,14). Furthermore, it is not clear if concurrent training increases fatfree mass and/or decreases fat mass and whether it improves metabolic parameters in obese adolescents.
Thus, the purpose of the present study was to ana lyze the effects of a 20week concurrent training (20 WCT) intervention program on body composition and metabolic variables, according to gender, in obese ado lescents.

Subjects
The subjects were invited through television and newspa per advertising to participate in a weight loss intervention program for obese adolescents, conducted at the Univer sidade Estadual Paulista (Unesp) in Presidente Prudente, Brazil. The participants contacted the researchers by tele phone and an appointment was scheduled to take mea surements at the Universidade Estadual Paulista -Unesp in the Study Center and Laboratory of Assessment and Prescription of motor activity (Celapam).
The preliminary diagnosis of obesity was performed using body mass index (BMI) (15). After this prelimi nary diagnosis, the following inclusion criteria were used to select the subjects: i) aged 12 to 15 years; ii) no engagement in regular physical activity within the three months immediately prior to the study; iii) no restric tions on physical activity diagnosed by a medical doctor; iv) a consent form signed by the parents/guardians to participate in the study. One hundred and eighty obese children and adolescents (97 male and 83 female [aged 716 years]) contacted the researchers and the exercise protocol began with 80 subjects who met all the inclu sion criteria. After 10 weeks of study, the sample had a loss of 50% subjects (n = 40) due to intervention time and duration, number of missed sessions, health pro blems and/or termination without justification. Finally, only 25 subjects (13 male and 12 female) concluded the 20 weeks exercise and evaluation protocol.
The present study was approved by the Ethical Re search Committee of the Universidade Estadual Paulis ta -Campus of Presidente Prudente (Unesp) (protocol number 07/2009).

Body composition
Dual-energy x-ray absorptiometry (DEXA) After the preliminary diagnosis of obesity through BMI, body composition (wholebody and segmental) was estimated using dualenergy Xray absorptiometry (DEXA) (Lunar DPXNT scanner [Lunar DPXNT; General Electric Healthcare, Little Chalfont, Bucking hamshire, United Kingdom] software version 4.7). Fat free mass (FFM), percentage trunk fat mass (TFM%) and percentage fat mass (%FM) were estimated. All measurements were carried out at the laboratory of the university in a climatecontrolled room and the equip ment was calibrated every morning, as recommended by the manufacturer.

Intra-abdominal adipose tissue
An ultrasound examination of the upper abdomen was performed to measure intraabdominal adiposity (IAAT). The examination was performed by only one qualified radiologist, using a TOSHIBA Eccocee with a 3.7 Mhz convex transducer. All adolescents were in structed to fast for 4 hours prior to the evaluation, ac cording to medical literature.

Blood samples
Blood samples were collected from subjects in tubes containing EDTA after a 12 hours fasting period. All blood sample collections (performed by nurses) and biochemical analyses were carried out in a private labo ratory. Fasting blood measurements were performed using the colorimetric method. Total cholesterol (TC), highdensity lipoprotein cholesterol (HDLc), low density lipoprotein cholesterol (LDLc), triglycerides and plasma glucose were analyzed (16).

Blood pressure
Measurements of systolic blood pressure (SBP) and diastolic blood pressure (DBP) were performed using automatic equipment (Omron HEM 742) on the right arm with the subject lying down, resting and after a 15 minutes rest period.

Training program
The exercise protocol was based on 30minute sessions of aerobic activities (walking and jogging) followed by 30 minutes of strength exercises (resistance training), three times per week, over a period of 20 weeks (17).
The 10repetition maximum (10RM) protocol was used to predict the maximum amount of resistance that could be actively overcome in 1 repetition. The strength exercises were: 45degree leg press, seated row, chest press, squat, upper chest, leg workout, bicep curl, pec deck, triceps extension, quadriceps extension, sit ups and dorsal raise. The periodization for aerobic exercise was com posed of four weeks of adaptation, concomitant with strength exercises in the same session, which consist ed of low/moderateintensity walking for 30 minutes without heart rate control. After these four weeks, the aerobic activities (walking and jogging) were adjusted according to the maximum heart rate (65% to 85%) va lues provided by the maximal oxygen consumption test. The aerobic activities were performed on a running track with each workload specific to each individual.
The intensity of aerobic exercise was monitored us ing a heart hate monitor (Polar ® S810), placed, ran domly, on four individuals per session. The participants were advised to drink water and wear appropriate exer cise clothing.

Statistical analysis
Data normality was verified using the Kolmogorov Smirnov test. Numerical variables were presented as mean, standarddeviation and delta percentage (Δ%) of the difference between time points. The sphericity of the data was verified by the Mauchly´s test. When the spheric ity was not found the GreenhouseGeisser correction was used. An analysis of variance (ANOVA) for repeated mea sures was used to compare the three time points (baseline, 10 weeks and 20 weeks). To check for possible differences between time points, the Bonferroni posthoc test was used. Statistical significance was set at pvalue <5% and the statistical software SPSS (15.0) performed all analyses.

RESULTS
The descriptions of the sample for metabolic variables and body composition are shown in table 1 for males  and table 2 for females and it can be seen that the sam ple was composed of obese individuals by the combined analysis of all anthropometric variables. Parametric samples were presented as mean and standard deviation (mean ± SD) and nonparametric samples as median and interquartile range, according to gender, at base line, after 10 weeks and after 20 weeks of intervention. Table 1 demonstrates, through mean and standard deviation, alterations between baseline, the 10 initial weeks and the 10 final weeks in the male group. Re ductions in BMI zscore (Δ%= 3.9; p = 0.

DISCUSSION
From the results of the present study it was possible to verify that concurrent training promoted significant beneficial alterations in body composition and metabo lic variables in both genders. Significant improvements were also observed in lipid profile variables, in which the female gender demonstrated greater reductions. Recently, the American College of Sports Medicine (14) stated that there is a lack of evidence to indicate that strength training, without aerobic exercise or di etary control, is sufficient to promote weight loss and, therefore, its utilization in combination with aerobic activities is recommended. According to studies carried out with young girls, the combination of aerobic and strength exercises is more effective at decreasing body adiposity than either nutrition or one of these models of exercise in isolation (18). Physical training is able to promote weight loss, as well as decreasing fat mass and increasing fatfree mass relative to the intensity of exercise (19). Losing weight and promoting healthy slimming requires moderatein tense exercise for about 60 minutes (14). LeMura and Maziekas (20) demonstrated that superior alterations in body composition of obese children and adolescents occurred as a result of concurrent training (aerobic and strength exercises) when performed at lowintensity over a longduration.
The training protocol in the present study was con sidered as lowmoderate intensity and significant im provements were observed in variables related to body composition, with significant decreases in percentage of adipose tissue and trunk fat mass, in both genders. However, the gain or reduction in these variables oc curred at different time points in the intervention. In addition, the greatest reduction was observed when comparing the results after 20 weeks of intervention (total time) with the baseline in both groups.
In a study performed by Davis and cols. (18) with girls (15.2 ± 1.1 years) submitted to a pilot protocol of nutritional intervention and combined exercise (aero bic and strength), the authors observed that after 16 weeks of training there was a significant reduction of 3% in body adiposity corroborating with the present study that found a reduction of 3.4% after 20 weeks. According to research with boys, a combination of cir cuitbased resistance training and aerobic exercises over 12 weeks was responsible for a decrease of 2.2% in the percentage of body fat (21), however the results of the present study showed a reduction after the tenth week of intervention. Response to training in relation to total fat occurs differently between the sexes due to matura tional processes. In both genders, there is an increase in body weight in the final stages of maturation. In girls there is a proportional increase between fat mass and fatfree mass, while males demonstrate an increase in fatfree mass and a decrease in fat mass (22).
After the 20 weeks training protocol, significant re ductions in TFM% were observed in both the male and female groups. Studies that compare the effects of aero bic and anaerobic training in obese adolescents verified a decrease of 6.5% and 8.2% respectively (23). Several studies indicate that distribution of body fat may be an indicator of risk of cardiovascular diseases, alterations in blood pressure, cholesterol concentrations and glucose tolerance (2426), whereas individuals with higher fat deposits in the upper body are more likely to present an increased risk of cardiovascular diseases. However, ex ercise may be a strong tool for reducing diseaserelated accumulations of fat in the trunk region.
Regarding lipid profile, TC, LDLc and TG concen trations were positively affected by concurrent training, with significant decreases in all these metabolic param eters, except HDLc, in both genders. The improve ments in lipid profiles are directly related to the reduc tion in body mass and fat mass in the central regions of the body owing to decreases in free fatty acids and the formation of different lipoprotein molecules (27,28). In agreement with our findings for LDLc and TC, Foschini and cols. (29) found similar results for con current training after 14 weeks in obese youth. In the present study, the applied exercise protocol was com posed of activities of low (in the initial protocol) and moderate intensity. Kraus and Slentz (30) reviewed the scientific literature and identified that, although lipids are the principle fuel for sustaining activities of moder ate intensity, activities of low intensity have a relevant burden in the control of fasting serum lipids and should be encouraged in sedentary obese adolescents.
The present study suggested that intensity of effort may have influenced the positive effect of concurrent training, where lipid variables showed significant im provements after 20 weeks of intervention, except for HDLc. In agreement with the literature it is believed that this result was due to the intensity progression during training, where intensity remained low to mod erate in the first 10 weeks of training, as it was possible to observe decreased TG (baseline: 102.5; post: 77. When comparing results between genders, it was observed that both groups responded to training in the same variables, with significant alterations observed at the end of the intervention. A small difference was iden tified between the groups; male adolescents seemed to respond to training more quickly with a higher number of modifications after 10 weeks of the protocol. In a previous study by our group which analyzed the effects of concurrent training on risk factors and steatosis, sig nificant alterations were identified in height, percentage body fat, fat mass, fat free mass, percentage trunk fat, total cholesterol and LDLc (31), after 20 weeks. These findings suggest that this population requires a longer intervention time, given the limitations and biological stage, for significant changes to occur in body composi tion and lipid variables. In contrast, in the present study, it was demonstrated that after 10 weeks of intervention there were already significant enhancements in body composition and metabolic variables, regardless of gen der, suggesting that a shorter intervention time, when controlled, could be an effective strategy. However, comparisons between genders were not performed and this is suggested for future research projects.
The limitations of the present study should be high lighted. The absence of a sedentary control group, ac cording to gender, in addition to the fact that dietary habits were not recorded, are potential confounders of the results obtained. However, this study considered the biological individuality of the participants, priori tizing physiological, morphological and maturational features, according to gender, and comparing individu als at different moments of the intervention period. In addition the absence a maximal oxygen uptake test in the intermediate moment (10 weeks) and other meta bolic profiles, such as insulin, were a limitation to better interpretation of the results.
In summary, our results identified that concurrent training seems to be an effective exercise protocol, able to promote significant improvements in body composition and metabolic variables, by decreasing fat free mass and trunk fat mass, and consequently BMI and BMI zscores, and enhancing lipid profile variables, by reducing triglyc erides, total cholesterol and LDLc, for both genders.