Abstract
Background: Previous studies have observed significant heterogeneity in the magnitude of change in measures of metabolic response to exercise training. There are a lack of studies examining the prevalence of non-responders (NRs) in children while considering other potential environmental factors involved such as biological maturation.Aim: To compare the effects and prevalence of NRs to improve the insulin resistance level (by HOMA-IR), as well as to other anthropometric, cardiovascular, and performance co-variables, between early (EM) and normal maturation (NM) in insulin-resistance schoolchildren after 6-weeks of HIIT.Methods: Sedentary children (age 11.4 ± 1.7 years) were randomized to either HIIT-EM group (n = 12) or HIIT-NM group (n = 17). Fasting glucose (FGL), fasting insulin (FINS) and homeostasis model assessment of insulin resistant (HOMA-IR) were assessed as the main outcomes, as well as the body composition [body mass, body mass index (BMI), waist circumference (WC), and tricipital (TSF), suprailiac (SSF) and abdominal skinfold (AbdSF)], cardiovascular systolic (SBP) and diastolic blood pressure (DBP), and muscular performance [one-repetition maximum strength leg-extension (1RMLE) and upper row (1RMUR) tests] co-variables were assessed before and after intervention. Responders or NRs to training were defined as a change in the typical error method from baseline to follow-up for the main outcomes and co-variables.Results: There were no significant differences between groups in the prevalence of NRs based on FGL, FINS, and HOMA-IR. There were significant differences in NRs prevalence to decrease co-variables body mass (HIIT-EM 66.6% vs. HIIT-NM 35.2%) and SBP (HIIT-EM 41.6% vs. HIIT-NM 70.5%). A high risk [based on odds ratios (OR)] of NRs cases was detected for FGL, OR = 3.2 (0.2 to 5.6), and HOMA-IR, OR = 3.2 (0.2 to 6.0). Additionally, both HIIT-EM and HIIT-NM groups showed significant decreases (P < 0.05) in TSF, SSF, and AbdSF skinfold, and similar decreases in fasting insulin and HOMA-IR. The HIIT-EM group showed significant decreases in SBP. The HIIT-NM group showed significant increases in 1RMLE and 1RMUR. A large effect size was observed for pre-post changes in TSF in both groups, as well as in SSF in the HIIT-NM group.Conclusion: Although there were no differences in the prevalence of NRs to metabolic variables between groups of insulin resistance schoolchildren of different maturation starting, other NRs differences were found to body mass and systolic BP, suggesting that anthropometric and cardiovascular parameters can be playing a role in the NRs prevalence after HIIT. These results were displayed with several metabolic, body composition, blood pressure, and performance improvements independent of an early/normal maturation or the prevalence of NRs.
Highlights
The benefits of exercise on health and performance are mainly expressed in terms of the “mean,” but there is wide interindividual variability in response to exercise training (IVRET) that has not been fully clarified in adults (Sisson et al, 2009; Bouchard et al, 2012; Álvarez et al, 2017b; Montero and Lundby, 2017) and not explored in children
A large statistical effect size was found for TSF in both the high-intensity interval training (HIIT)-EM (−1.40; 90% CI = −2.17, −0.64) and HIIT-NM group (−1.31; 90% CI = −1.80, −0.82) (Figure 2E), as well as for SSF in the HIIT-NM group (−1.24; 90% CI = −1.55, −0.92) (Table 1)
This study has four main results: (i) there were no significant differences between children with EM and NM in the prevalence of NRs based on improved metabolic profiles; (ii) independent of NRs prevalence and biological maturation (i.e., EM, NM), HIIT was able to decrease fasting insulin and homeostasis model assessment of insulin resistance (HOMA-IR) in insulin-resistance schoolchildren; (iii) there were significant differences in NRs prevalence in terms of anthropometric and systolic BP co-variables; and (iv) HIIT promoted improvements in the body composition, decreased systolic BP, and muscular performance co-variables included in this study
Summary
The benefits of exercise on health and performance are mainly expressed in terms of the “mean,” but there is wide interindividual variability in response to exercise training (IVRET) that has not been fully clarified in adults (Sisson et al, 2009; Bouchard et al, 2012; Álvarez et al, 2017b; Montero and Lundby, 2017) and not explored in children. The mean of a group may indicate decreased fasting glucose after training, individuals in this group could show no changes or a worsened response and would be considered as NRs in terms of fasting glucose (Alvarez et al, 2017a) (in press Frontiers). Other authors have described that under the same HIIT regime and under different health status conditions, there is different prevalence of NRs (i.e., percentage of NRs cases) to decrease both fasting glucose and fasting insulin metabolic variables in adults (Alvarez et al, 2017a). There are a lack of studies examining the prevalence of non-responders (NRs) in children while considering other potential environmental factors involved such as biological maturation
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