Changes in children’s cardiorespiratory f itness and body mass index over the course of the COVID-19 pandemic: a 34-month longitudinal study of 331 primary school children

Gerald Jarnig ·Reinhold Kerbl·Mireille N. M. van Poppel

In late 2019,heavy restrictions were enforced on public activities worldwide to diminish the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)virus [1].

These restrictions,which included school closures and strictly limited sports and leisure opportunities,particularly impacted children and adolescents [2].Lifestyle changes in children and adolescents led to reduced physical activity levels [2,3],increased sedentary behavior [3,4],changes in eating habits,and changes in sleep habits [3].These subsequently affected important health parameters,such as body mass index (BMI) and cardiorespiratory f itness(CRF) [5— 8].We previously reported a reduction in CRF and an increase in BMI in 7—9-year-old children in Austria after the implementation of COVID-19-related restrictions in schools [9— 11].

Here,we report how these important health markers [12,13] developed in this cohort of children after the relaxation of COVID-19 mitigation measures.We analyzed data from September 2019 (pre-COVID-19),June 2021 (shortly after the abolishment of COVID-19-related restrictions),and June 2022 (1 year after the termination of mitigation measures).The study was registered in the German Clinical Trials Registry and approved by the local Research Ethics Committee (GZ.39/23/63 ex 2018/19).Informed consent was obtained from the parents or legal guardians of the participants.For monitoring CRF,we used the 6-min run test,and BMI was standardized using Austrian reference centile curves,as described by the novel Austrian f itness monitoring tools (AUT FIT) [14].Changes in the period during the stringent mitigation measures (Sept 2019—June 2021,P1),for the period after the relaxation of the stringent measures(June 2021—June 2022,P2),and for the whole study period(Sept 2019—June 2022,WSP) were calculated.We examined differences in subgroups by gender and sports club membership.Statistical analysis was performed using SPSS software(Version 28).All the tests were two-sided;aPvalue <0.05 was considered signif icant.

A total of 331 children (mean age in September 2019 7.7 ± 0.4 years,range=7—9 years) participated at all measurement time points.Among them,159 (48.0%) were girls,and 146 (44.1%) were members of a sports club.Between September 2019 and June 2022 (WSP),the BMI score increased from 22.19 to 22.56 (P<0.001).The highest BMI was observed at the end of P1 in June 2021 (22.82),while after the relaxation of the restrictions,BMI showed a signif icant decrease (P=0.001) (Fig.1,Table 1).

Table 1 Data for BMI and CRF over measurement time points Sep19,June 21 and June 22

Fig.1 Changes in body mass index (EQUI BMIAUT) from September 2019 to June 2022.P1 period with stringent mitigation measurement,P2 period after relaxation of mitigation measurements,BMI body mass index,EQUI BMI AUT equivalent BMI based on Austrian reference centile curves passing through adult BMI values,A all,♀ girls,♂ boys,SC member sports club,NSC not member sports club

Signif icant gender differences were found.Changes in BMI among girls were not statistically signif icant in any period.In boys,there were highly signif icant increases in BMI values during P1 (P<0.001),followed by a strong decrease in P2 (P<0.001).However,in June 2022,BMI in boys was still higher than in September 2019 (P<0.001).

Both children with and without sports club membership showed a highly signif icant (P<0.001) increase in BMI values in P1.In P2,a pronounced reduction (P=0.003) was found in children who were members of a sports club.In contrast,children without sports club membership showed only a small,nonsignif icant (P=0.21) reduction in BMI values during P2,with no return to baseline values by the end of the observation period (June 2022).

When analyzing CRF,we found an extreme decrease during P1 (P<0.001) in all subgroups (Fig.2,Table 1).After the cessation of stringent mitigation measures during P2,signif icant improvements were found (P<0.001)in the total group.Improvement was statistically signif icant in the subgroup of girls (P=0.002) and in children without sports club membership (P=0.002);however,this improvement was nonsignif icant in boys (P=0.08) and in children attending a sports club (P=0.08,Fig.2,Table 1).None of the subgroups returned to pre-COVID levels of CRF.Further information is given in the supplementary material in Supplementary Tables 1—6.

Fig.2 Changes in cardiorespiratory f itness (6MR) from September 2019 to June 2022.P1 period with stringent mitigation measurement,P2 period after relaxation of mitigation measurements,6MR six-minute run,SDS standard deviation score,A all,♀ girls,♂

Our observation of increasing BMI and decreasing CRF during P1 and improvement in both outcomes during P2 suggests that the negative effects of the pandemic and its mitigation measures on BMI are reversible,at least in primary school children.

However,it is important to note that a full reversal of the negative effects of the pandemic was not achieved,particularly in boys.This highlights the need for further action in addressing these issues in the future.Failure to do so might result in long-term deleterious public health consequences,most likely resulting in high socioeconomic burden and possibly even costing numerous life years.

（二）加大资金统筹使用力度，合理确定投资规模。基本建设所需资金属于财政支出，应当按照公共财政的支出原则统筹管理使用，防止资金使用分散化和低效益。应通过建立“政府领导、财政牵头、部门配合”的机制，逐步形成投向科学、结构合理、管理规范、运转高效的资金使用管理机制。就具体项目而言，按照“一个盘子进，一个口子出”的要求，以项目为中心，按照“渠道不乱、用途不变、统筹安排、形成合力”的基本要求，整合多渠道资金，集中力量办大事，并根据实际需要和财力可能，在项目决策审批之前合理确定基本建设投资规模。

Together with other studies [15,16],our findings provide a basis for policymakers to more carefully consider the advantages and disadvantages of virus mitigation measures in the future.The benefit of such measures in terms of virus transmission must be balanced against long-term sequelae,such as BMI increase and fitness decrease as markers of physical health.The continued performance of physical activities should be considered as important as infection prevention,especially in school settings.For possible future pandemic periods,any associated closures of sports clubs and public playgrounds should at least guarantee the minimum level of physical activity recommended by the World Health Organization(60 minutes of moderate exercise daily) [17],preferably outdoors during school hours.

To continuously diminish the negative effects of the(hopefully) vanishing COVID-19 pandemic,a variety of school-based interventions should be scheduled.These measures should include a daily physical activity unit,healthy lunch,and the implementation of a health monitoring system in schools to verify the efficacy of such measures.Moreover,participation in sports clubs should be actively encouraged for school children and adolescents.Ultimately,policymakers need to recognize the importance of such programs,actively promoting and supporting their implementation.

Supplementary InformationThe online version contains supplementary material available at https:// doi.org/ 10.1007/ s12519-023-00772-0.

AcknowledgementsThis study was organized by the non-prof it association NAMOA—Nachwuchsmodell Austria.The authors would like to thank all participants and their guardians;the trainers and staffof this study;Wolfgang Modritz for the initiation of this study;none of the individuals listed were f inancially compensated.

Author contributionsJG: conceptualization,methodology,formal analysis,investigation,resources,data curation,writing—original draft,writing—review and editing,visualization,project administration.KR: writing—review and editing,visualization.vPMNM: conceptualization,formal analysis,writing—review and editing,visualization,supervision.All authors have read and agreed to the published version of the manuscript.

FundingThis research was funded by the Austrian Federal Ministry for Arts,Culture,Civil Service,and Sport,Grant number GZ2021-0.361.671.The open access was funded by the University of Graz.

Data availabilityData can be requested from the corresponding author and are provided free of charge for non-commercial purposes.

Declarations

Conflict of interestMr Jarnig was receiving grants from the Austrian Federal Ministry for Arts,Culture,Civil Service and Sport during the conduct of the study.No other conf licts of interest were reported.

Ethical approvalThis study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Research Ethics Committee of the University of Graz,Styria,Austria (GZ.39/23/63 ex 2018/19).All participants gave their consent to participate in the study.

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