The main findings of the study suggest that: (a) no mean changes were found in adiponectin, effect suggests a trivial change in the HIIT and possibly beneficial in the MICT, as well as no difference was in the frequency of responsiveness; (b) in the adiposity, HIIT showed mean changes and trivial effect, however CG showed frequency of non-respondents; (c) in the cardiometabolic risk, beneficial changes were observed in the HIIT, and harmful in the CG. CRP there was a frequency of respondents in the HIIT and MICT and non-responsiveness for the CG; and (d) in physical fitness, the HIIT and MICT showed mean changes, beneficial effects, and frequency of responsiveness, while CG of non-responsiveness.
Our results confirm the importance of exercises be considered as non-pharmacological therapy in adolescents with obesity and in the prevention of associated. Benefits of exercise include adaptations in metabolic parameters, reduction of inflammatory adipocytokines and increase in anti-inflammatory, crucial factors considered in the treatment of obesity-related complications [2–4, 9]. Due to the importance of inter-individual variability, it was verified the frequency of responsiveness, considering each intervention and specificity of each adolescent's response to exercises. Evidence has observed the frequency of responsiveness post-exercise on physical and cardiometabolic health [10–13, 19], and to our knowledge, no published research has analyzed the responsiveness of adiponectin post-exercise in overweight adolescents.
Studies have verified the effect of exercises on adiponectin in different age groups and clinical conditions. In adults, metanalysis found that aerobic exercise demonstrated an influence on adiponectin in overweight individuals [20]. Studies in the pediatric population have shown an increase in the adiponectin [6, 9], while others did not report changes [4, 21, 22]. Differences are related to changes in body composition [2], indicating that exercise was more effective in influencing adiponectin concentrations in those with the greatest reduction in body fat.
We did not find differences in adiponectin in the groups, and the effect of HIIT was trivial, while in the MICT an effect was found possibly beneficial, even in the MICT that did not promote reduction in fat mass. Results similar to those found in girls, that no increase in adiponectin was observed, even with reduction in body fat after combined exercise [4], and after lifestyle intervention and moderate intensity of continuous [22]. School intervention of moderate to vigorous exercise did not find an increase in the adiponectin, while a reduction in the percentage of trunk fat was observed, but not the percentage of total fat [21]. Evidencing the probable influence of the body fat distribution as a determinant of adiponectin concentration in obese. Conversely, adiponectin is more related to abdominal fat than to other fat deposits, whereas gluteofemoral fat appears to exert a protective effect [23].
Furthermore, the exercise groups did not show differences in frequency of respondents and non-responders in relation to adiponectin and adiposity, but chances of responsiveness were observed for adiponectin in HIIT and MICT compared to the CG, as well as a prevalence of non-responders was observed for WC and WHtR in the CG. Our results confirm that the lack of regular exercise can be harmful to overweight adolescents, changes that negatively impact of cardiometabolic health, consequently, on the reduced physical fitness in those who do not benefit from exercise [12, 13, 19]. Studies have shown that the regular practice of exercises can promote beneficial effects in the adiposity and body fat [4, 9, 13].
Different from our results in MICT, it was observed reduction on central adiposity after multidisciplinary intervention with higher volume aerobic exercise [13]. Reinforcing the importance of the time of weekly practice to provide favorable effects in the reduction of adiposity, since the accumulated volume was double what was used in our study, which totaled 150 minutes weeks. Therefore, it seems that the volume of training may be a determining factor in interventions that seek to reduce adiposity. Thus, higher volume exercise can lead to temporary appetite suppression, helping to regulate energy balance and caloric deficit [24], as well as greater reduction in adiposity in obese children for programs long term (> 24weeks) [9].
We found in the HIIT reduction in CRP, a protein associated with low-grade chronic inflammation, probably associated with a reduction in adiposity. Frequency of responsiveness was observed in HIIT and MICT, demonstrating that adolescents responded favorably in reducing the subclinical inflammatory process associated with obesity, even though the mean value of the MICT did not show a notable change. Also in the CG, a frequency of CRP non-responsiveness was observed. HIIT a trivial effect was observed in the increase of adiponectin, and possibly beneficial effect on MICT. However, no differences were found in the adiponectin in the mean values and the prevalence of responders for groups. Results suggest that the anti-inflammatory effect of adiponectin, may be crucial according to metabolic demand, and possibly, its concentration presents stable levels in adolescents who do not need its protection, since HIIT promoted changes in adiposity and in the inflammatory process.
Therefore, after intervention with exercises, obese adolescents who present reductions in adiposity and/or in the inflammatory process, there is no need to increase the secretion of adiponectin for metabolic protection, demonstrating that exercise can play a decisive role in the relationship with adiposity [12]. Changes that occur in the microenvironment of adipocytes and their anti-inflammatory response can inhibit the expression and secretion of adiponectin, which seems to be mediated by the secretion and expression of pro-inflammatory cytokines [25]. Thus, inflammation is considered an important risk factor in the pathophysiology of obesity, insulin resistance and hypertension, contributing to the hyperactivation of the sympathetic nervous system and the renin-angiotensin-aldosterone system [26].
Mechanisms by which exercises can influence the adiponectin have not yet been fully elucidated. In addition to reducing fat mass [2], exercise may lead to upregulation of AdipoR1 and AdipoR2 receptors, which could result in a reduced need for adiponectin. Or, could alter its proportions of its isoforms, decreasing the medium molecular weight and increasing the high molecular weight, indicating that it may be more important to measure its isoforms [27]. Nielsen et al. [28] contribute the hypothesis that adiponectin is secreted as a compensatory mechanism for low levels of exercise. We demonstrate that adolescents who participated in the exercise showed increase and responsiveness in cardiorespiratory fitness. This increase could influence so that there was no increase in adiponectin, demonstrating that cardiorespiratory fitness can play a moderating role in these relationship with adiponectin.
Recently, it has been shown that adiponectin is also a myokine, produced and released by skeletal muscle [29], stimulating the autophagic flow, and in case of autophagy activation, affect muscle function, playing a key role in muscle fibers and skeletal muscle dysfunction [30]. The effect of adiponectin on skeletal muscles is like the action signaled by insulin, decreasing insulin secretion and hepatic glucose production [31]. Reduction in adiposity and the increase in physical fitness can increase in adiponectin. Our results demonstrate increase in the muscular fitness, as well as frequencies of responders. Thus, we can consider that muscular fitness could also influence so that there was no increase in adiponectin.
We emphasize that in our study, the measurement of adiponectin was performed in its entirety, and not its isoforms, which may influence the results. Evidence has suggested that high molecular weight adiponectin better reflects obesity-related metabolic abnormalities than total concentration [27,32]. However, studies also show divergences, while Ciccone et al. [32] found that high molecular weight adiponectin was related to cardiovascular risk in overweight children, Nascimento et al. [21] even after eight months of intervention with exercise in obese children and adolescents, they did not observe differences in the adiponectin and its isoforms.
The behavior observed in the adiponectin can vary in a non-linear way, according to the degree of adiposity, inflammatory process, and physical fitness. We observed that there are higher concentrations of adiponectin when the levels of adiposity, and physical fitness are adequate, indicating that the regular practice of exercises can play a decisive role in the relationship with adiposity and inflammatory process. Obese adolescents probably show lower concentrations of adiponectin because they have an altered cardiometabolic profile, and for there to be an increase in its secretion, we found that there is a need to establish threshold points for levels of physical activity and physical fitness.
Study has some limitations that must be considered, such as the selection of adolescents, and the sample size, the generalization of the results must be carried out with caution. The measurement of adiponectin was the total and we considered a single measurement, and it is possible that it does not accurately reflect its state, as it results from several tissues, we question to what extent skeletal muscle can contribute. Nutritional variables and other variables on the adolescents' lifestyle were not included, which could influence the analyses. Genetic factors that may be determinants of inter-individual variability were not verified. We suggest that interventions aimed at reducing and controlling obesity and associated factors in adolescents should be encouraged to redirect future adults towards a better health profile.
In conclusion, we found that exercise intervention programs of different intensities did not change adiponectin concentrations and adolescents did not show frequency of individual responsiveness. However, in adolescents who did not benefit from the practice of exercises in the intervention, harmful effects and greater chances of non-responsiveness were observed, highlighting that the lack of regular exercise practice can be harmful, negatively impacting cardiometabolic risk factors and physical fitness.