1 Introduction
The prevalence of overweight and obesity has increased in recent decades and remains high among children and adolescents.[1] [2] [3]
Traditionally, continuous aerobic exercise in children, characterized as moderate intensity exercise without rest intervals, has been the most common type of exercise recommended to improve body composition, cardiorespiratory fitness (CRF) and overall health-related parameters[4–6] [7]
Recently, interest in higher intensity interval training (HIIT) research has increased. HIIT has been identified as a time-efficient type of exercise to promote health benefits and improve fitness.
Numerous meta-analyses have reported that HIIT leads to improvements on body composition[8] [9–11] [5] [7,12]
Particularly, there is limited evidence related to outcomes of intermittent exercise. It is discussed that it may be more appropriate for children because their physical activity patterns are naturally intermittent.[13]
Therefore, the aim of this study protocol is to provide a clear, standardized and transparent methodology for performing a systematic review and meta-analysis aimed to assess the effect of HIIT programs versus non-training Control Groups (CGs) on body composition, cardiometabolic risk factors and CRF in healthy children.
2 Methods
2.1 Protocol and registration
This systematic review and meta-analysis protocol is based on the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement[14] [15]
The meta-analysis study was registered with the PROSPERO International Prospective Register of Systematic Reviews Database (CRD42018093432).
2.2 Search strategy
Relevant randomized controlled trials (RCTs) will be searched in MEDLINE (via PubMed), EMBASE (via Scopus), SPORTDiscus, Cochrane Library, and Web of Science databases RCTs with language restriction in Spanish and English. In addition, the literature search will be complemented by manual screening references included in articles that are considered eligible for the systematic review. Study records will then be managed using the Mendeley reference manager. The search strategy will include free text terms, combining Boolean operators from the relevant concepts presented in Table 1 .
Table 1: Full-search strategy for MEDLINE database.
2.3 Eligibility criteria
2.3.1 Study design
All relevant RCTs assessing HIIT to improve body composition, cardiometabolic risk factors and/or CRF in children, in which the CG did not receive any PA intervention will be included. Observational, prospective cohort studies systematic reviews, and RCTs performed with adolescents or adults will be excluded.
2.3.2 Participants
The studies must include healthy schoolchildren aged 5 to 12 years.
2.3.3 Interventions
The included studies must involve interventions of HIIT, prescribing high intensity exercise if
(1) the intensity was >= 90% peak oxygen consumption[16] 2peak );
(2) had an intensity that was >= 100% maximal aerobic speed[17] peak ).[18,19]
2.3.4 Outcomes
The primary outcomes will be the following: changes in body composition assessed with body mass index (BMI) and body fat percentage; changes in the levels of some of cardiometabolic risk factors such as systolic and diastolic blood pressure, total cholesterol, low-density lipoprotein cholesterol (LDL-c), high-density lipoprotein cholesterol (HDL-c), glucose, triglyceride and changes in the CRF assessed as maximal oxygen consumption (VO2max ), VO2peak , maximal HR (HRmax ) and HRpeak.
2.4 Selection of studies and data extraction
After excluding duplicated records, 2 researchers will independently evaluate the titles and abstracts of the retrieved articles to identify eligible studies for the systematic review. Abstracts that meet inclusion criteria or that do not provide enough information regarding the inclusion/exclusion criteria will then be evaluated through a full-text reading. Then, 2 researchers will examine the included and excluded studies to verify the reason for each decision. Inconsistencies between these 2 researchers regarding selection will be resolved by a third researcher, who will make the final decision. The selection process of eligible articles is shown in Figure 1 .
Figure 1: The study selection will be conducted according to the PRISMA statement. PRISMA = preferred reporting items for systematic reviews and meta-analyses.
The data extraction will be carried out by 2 independent reviewers in accordance with the standardized sheet recommended by the Cochrane Handbook of Systematic Reviews of Interventions. The following information will be extracted from the included studies:
(1) first author's name,
(2) year of publication,
(3) characteristics of participants (number, age, weight status),
(4) HIIT and CG protocols (type, duration, modality, and intensity), and
(5) results of the means and standard deviations of body composition, cardiometabolic risk factors and CRF variables from pre- to post-intervention between groups (HIIT vs CG).
2.5 Missing data dealing with
When we encounter missing or unclear data, we will try to contact corresponding authors for additional information.
2.6 Risk of bias assessment
Two independent researchers will be blinded to the authors, titles and years of publication of the included studies to evaluate the risk of bias of each included study. The risk of bias assessment will be conducted using the RoB 2.0 tool developed by the Cochrane Collaboration.[20]
2.7 Data analysis and synthesis
Meta-analyses will be conducted to determine the effect of HIIT on body composition, cardiometabolic risk factors, and CRF variables, in comparison to nontraining CGs. For studies that include both non-training CGs and continuous moderate intensity exercise comparison groups, only the CG data (without physical activity intervention) will be included in the meta-analysis.
The effect size (ES) of each study will be calculated as the standardized mean differences in the variables from pre- to post-intervention between groups (HIIT vs CG) using random-effects model[21]
The heterogeneity results across studies will be evaluated using the I 2 statistic, and the following values will be used for its interpretation: 0% to 30% “not important” heterogeneity; >30% to 50% “moderate” heterogeneity; >50% to 80% “substantial” heterogeneity, and >80% to 100% “considerable” heterogeneity. The corresponding P -values will be also considered.[15]
For each pooled ES, we will be conducted a sensitivity analysis by removing the studies one by one to assess the robustness of the summary estimates and to detect whether any study accounted for a large proportion of heterogeneity. Finally, visual inspection of funnel plots and the Egger test will be conducted to detect publication bias.[22]
A lineal meta-regression analysis will be used to explore whether covariates could be associated with the magnitude of the effect and could explain the observed statistical heterogeneity.[15]
In addition, subgroup analyses will be performed, if it is possible, to assess whether the weight status influences the overall ES. All analyses will be perform using Comprehensive Meta-analysis Software (2nd version, Biostat, Englewood, NJ) and StataSE software, version 15 (StataCorp, College Station, TX).
3 Discussion
To the best of our knowledge, this is the first systematic review and meta-analysis protocol to examine the effect of HIIT interventions on body composition, cardiometabolic risk factors and CRF in healthy schoolchildren aged 5 to 12 years. HIIT could be considered a more effective and time-efficient intervention for improving cardiometabolic health maskers in children compared with a non-exercise CG.
Several meta-analyses have assessed the effectiveness of physical activity interventions to improve cardiometabolic risk factors[23] [24] [25]
Furthermore, the results of this study will provide rigorous summary evidence about the effects of HIIT interventions on body composition, cardiometabolic risks factors such as blood pressure, BMI, HDL-c, LDL-c, triglycerides, glucose, total cholesterol, and CRF in healthy children.
4 Limitations
Different issues should be acknowledged as potential limitations: information and publication bias, insufficient methodological quality, scarce of statistical analysis, inclusion of articles in English and Spanish exclusively and inadequate reporting of methods and results. To try to avoid these possible limitations, we will take into account potential risks of bias for each study and we will follow the existing guidelines included in the PRISMA[14] [15]
5 Ethics and dissemination
Due to the nature of systematic review and meta-analysis, patients’ informed consent and ethic approval will not be required. The results obtained of this study could be particularly useful because they will provide rigorous evidence regarding the effect of HIIT interventions to improve the children's cardiometabolic health.
Author contributions
Conceptualization: Solera-Martínez, M, Pozuelo-Carrascosa DP.
Data curation: Solera-Martínez M, Díez-Fernández A, Pozuelo-Carrascosa DP.
Formal analysis: Solera-Martínez M.
Investigation: Solera-Martínez M, Manzanares-Domínguez I, Pozuelo-Carrascosa DP.
Methodology: Solera-Martínez M, Díez-Fernández A, González-García A, Pozuelo-Carrascosa DP.
Project administration: Solera-Martínez M, Pozuelo-Carrascosa DP.
Supervision: Martínez-Vizcaíno V.
Writing – original draft: Solera-Martínez M, Pozuelo-Carrascosa DP.
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