Absolute and relative intensity physical activity of children with healthy and low levels of cardiorespiratory fitness

Introduction Accelerometer-derived outcomes describing physical activity (PA) volume and intensity distribution relative to a person’s maximal capacity have provided insight into associations with health in adults. Little is known, however, about how the relative intensity of children’s PA volume and intensity distribution relates to health or fitness. To address this, we examined associations between children’s absolute and relative PA volume and intensity distribution with cardiorespiratory fitness (CRF), and differences in these PA outcomes for children stratified by CRF level.

In 9–10-year-old children (N=235) PA was assessed using wrist accelerometers for up to 7-days and CRF estimated from the 20-m multistage shuttle run test (20mSRT). Children were classified as Healthy or Low CRF. Absolute PA outcomes were PA volume (average acceleration; AvAccabs) and intensity distribution (intensity gradient; IGabs). Equivalent relative PA outcomes were generated (AvAccrel and IGrel) using maximum acceleration values derived from the 20mSRT.

Absolute, but not relative standardised PA outcomes were positively associated with CRF (AvAccabs Stdβ=0.21, p=0.02; IGabs Stdβ=0.21, p=0.03). Absolute standardised PA outcomes were significantly higher among Healthy CRF children (AvAccabs Stdβ=0.40, p=0.007; IGabs Stdβ=0.46, p=0.008), but there were no significant differences between Healthy and Low CRF groups for relative PA outcomes.

Children were similarly active relative to their physiological capacity, despite children with Healthy CRF being more active in absolute terms. Future studies should seek to better understand the influence of relative PA on CRF among diverse child populations who differ on a range of physical, physiological and demographic characteristics. Competing Interest Statement The authors have declared no competing interest. Clinical Trial ClinicalTrials.gov registration: NCT03283904 Funding Statement Yes Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethical approval was granted by Edge Hill University’s Research Ethics Committee (# SPA-REC-2015–330). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data Availability The data that support the findings of this study are openly available from the Open Science Framework https://osf.io/wnmvs/files/osfstorage