School-based interventions to increase physical activity and reduce cardiometabolic risk in children

Abstract

The three aims of the series of studies presented in this thesis were to investigate physical activity (PA) in childhood, the associations between PA and cardiometabolic (CM) risk in childhood, and interventions to promote PA in childhood.

Study 1 investigated the relationships between invasive and non-invasive markers of CM risk, and also examined the associations between individual CM risk markers and PA, cardiorespiratory fitness (CRF) and body composition in a cohort of school children (n = 101, 10 - 11.9 years) from Liverpool, England, and Belfast, Northern Ireland (NI). An individually calibrated approach to PA measurement was used to improve the classification of children's PA, and to clarify the associations between PA and markers of CM risk in children. Reference standard measurement techniques were used to assess body composition, PA and CRF. This range of high-quality objective measures is rarely observed in similar crosssectional studies with children. Few studies investigating CM risk in youth have included functional/pre-clinical' markers of CM risk, such as flow mediated dilation (FMD) and carotid intima media thickness (CIMT), or markers of inflammation such as adiponectin and C-reactive protein (CRP). Furthermore, few studies have investigated the associations between these preclinical markers of CM risk and invasive (inflammatory and metabolic) markers of CM risk in children. The inclusion of these measures enabled an investigation of the relationships between functional, metabolic and inflammatory components of CM risk in children. In Study 1, moderate to vigorous physical activity (MVPA) was positively associated with CRF in boys and girls, however, the associations between CRF and CM risk were higher than those observed between PA and CM risk. The associations between, PA, CRF, sedentary time (SED) and CM risk were often mediated by adiposity. The percentage of 10 - 11 year old boys (30%) and girls (22%) meeting current guidelines for daily MVPA was low. This study suggests that adiposity represents a suitable primary outcome measure to evaluate the effectiveness of interventions to improve CM health in children. Furthermore, as the associations between CRF and CM risk were higher than those observed between PA and CM risk, and a strong body of evidence suggests that vigorous PA is required to improve CRF in children, interventions to promote CM health in children should emphasise vigorous physical activities. This study also highlights the need for interventions to increase PA in primary school children.

Study 2 examined the effects of a multicomponent school-based PA intervention on PA levels, body composition and physical self-perception in a group of primary school children from NI (n = 99, mean age, 10.5 ± 0.5 years). The intervention was based on an extensive review of ‘effective’ multicomponent school-based PA interventions, and on recommendations from recent reviews and National Institute for Health and Clinical Excellence (NICE) guidelines. The intervention was designed to provide primary school children with both the knowledge of the benefits of PA, and the opportunity to be active during the school day. The intervention was teacher-led, and aimed to increase daily MVPA by incorporating classroom-based PA bouts throughout the course of the school day. In addition, the intervention included a curriculum component and outreach to families. Within the study, an individually calibrated approach was used to objectively assess children’s PA. This approach was used to clarify the associations between PA and health outcomes in children, and addresses the controversy and lack of consensus within paediatric research surrounding the selection of appropriate cut-off points to define PA intensity. To the author’s knowledge, the use of individually calibrated cut-off points in a study of a school-based intervention is novel. The study also used dual energy x-ray absorptiometry (DEXA) to assess pre- to post changes in body composition, and the Children and Youth Physical Self Perception Profile (CY-PSPP) (Whitehead, 1995) to assess changes in children’s physical self-perception. The combination of such high quality (reference standard) objective measures are rarely utilised in studies of school-based interventions. The intervention resulted in significant increases in school-time MVPA and school-time vigorous PA (VPA), and also significantly increased total daily MVPA and total physical activity (TPA) compared to matched controls. There were no significant effects of the intervention on measures of body size and composition, blood pressure (BP) or physical self-perception. This study suggests that future research designs should combine a greater duration of intervention (e.g. one academic year) with higher intensity (VPA) activities to increase total energy expenditure (TEE), utilise a ‘Whole-School’ model of health promotion and adopt a combined PA and diet strategy to prevent children becoming overweight in the long term.

Study 3 investigated the effects of child and parental feedback on promoting PA levels in a group of primary school children from NI (n = 85, mean age, 11 ± 0.3 years). In the study, participants were blinded to the accelerometer data that was collected, and did not receive iii rewards or incentives to increase PA. To the author’s knowledge, this is the first study to have utilised accelerometer data to provide feedback to children, and to a separate group of children and their parents/guardians, to examine the effect on children’s subsequent PA levels. There were no significant effects on PA when PA feedback was provided to either children, or to a group of children and their parents. However, the study provided novel insights into the short term effects of PA feedback in a group of children, and a group of children and their parents, and highlighted a number of unanswered questions about the usefulness of PA feedback in PA promotion in youth, and the role of child and parental awareness of PA in PA promotion. The study also provided further evidence that a significant proportion of primary age children in NI fail to meet current guidelines for daily MVPA. This study suggests that providing children and their parents with individual accelerometer feedback is not an effective strategy to promote children’s PA. However, the study had a number of limitations, and future research designs should take these, and the questions that have arisen from the study into account.

The studies in this thesis were consistent in reporting that the majority of primary age school children in NI did not meet current recommendations for daily MVPA. Study 1 highlighted a number of associations between children’s PA, CRF and markers of CM risk that were often mediated by adiposity. Obesity and type 2 diabetes have been found to be common in inactive children, and the prevalence of these diseases and disorders is increasing in NI. Study 2 increased total MVPA and total daily PA in primary school children through a theory-based multicomponent PA intervention. However, the increases in PA were short term, and highlight the need for well-designed interventions that promote long-term changes in children’s PA behaviour. Limitations in the design of the intervention were explored through the provision of PA feedback as a method of PA promotion in children in Study 3. Although the findings of Study 3 suggest that providing PA feedback to children and their parents was not an effective strategy to promote children’s PA, the study provided novel insights into the short term effects of PA feedback in children, and highlighted a number of important and unanswered questions about the usefulness of PA feedback in PA promotion in youth.

Date of Award	Sept 2014
Original language	English
Supervisor	Marie Murphy (Supervisor) & Gavin Breslin (Supervisor)