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.

The aim of this thesis was to investigate the relationships between BMI, and fitness in schoolchildren across Liverpool. This broad aim was approached using a series of six studies. Studies 1-4 took an epidemiological approach, with Studies 5-6 taking a laboratory approach using more sensitive measures to meet the overall thesis aim. The field-based fitness tests used to assess aspects of skill and health related fitness were found to be reliable for use in 9-10 year old children on a population or group level, although differing levels of reliability were observed between boys and girls, and some measures showed wide limits of agreement. Assessments of BMI over time (8 years) described significant increases in BMI from baseline. Despite significant increases from baseline, no significant increases in BMI were observed between the final three study years.

Health benefits are found to be associated with regular physical activity (PA), however, only a small percentage of young people are meeting the government physical activity recommendation guidelines. Therefore, there is a necessity to further understand the factors that may influence greater participation in physical activity. One essential influencing factor may be the level of mastery of motor abilities (MA) which children and adolescents need in order to participate in different physical activities. Therefore, this thesis was built on the hypothesis that children with better developed motor abilities may find it easier to be active and engage in more physical activity than those with less-developed motor abilities. This thesis provides three studies focusing on firstly, validating accelerometer counts against oxygen uptake (energy expenditure or EE) in 9 to 11 year old children performing a number of highly variable physical activities, similar to those undertaken in free-living conditions. Cut-off points for resting physical activity level, light physical activity level, moderate physical activity level and vigorous physical activity level were determined, which have been used to analyse PA data in studies 2 and 3. The second study was a cross-sectional design and third study was a longitudinal design. Both studies investigated the level of motor ability that 8 to 12 year old children possessed; secondly, they explored how anthropometric factors affected selected components of MA and thirdly, they determined whether MA components themselves and/or anthropometric measurements are useful predictors of physical activity levels. Results showed a strong correlation between the accelerometer counts and energy expenditure (as measured by oxygen consumption) of r = 0.86, and two different regression equations to predict EE from accelerometer counts were developed. Cut-off points of <61, 62 - 3435,3436 - 6100, and 2: 6101 were determined for resting, light, moderate and vigorous physical activity levels. The cross-sectional study showed that motor ability components were improved with increasing school year. Gender was the main predictor of most motor ability components; while body fat percentage (BF%) and age were secondary factors. The cross-sectional design does not allow the drawing of a causal relationship between the development of motor ability and physical activity levels. Thus, the longitudinal study illustrated that tracking motor ability and anthropometric data over time removed gender as a dominating factor in predicting the motor ability component as found in the cross-sectional study (Chapter 4). Changes in Standing Vertical Jump, Sit-up and Flamingo Balance Test were found to be factors that could affect change in physical activity levels. However, the small number of participants who met the criteria of physical activity intensity levels in this study mean that interpretations of results should be taken with caution. Further longitudinal research using a large group of children, motor ability component tests and more than one objective method to monitor physical activity levels are needed to clearly explore the relationship between these two parameters,

No description available.

Background: There is increasing evidence that low levels of physical activity may contribute to a range of poor health outcomes in children. Knowledge of the factors that might influence physical activity can inform the design of intervention studies and, ultimately, public health policy. Aims The aims of this thesis were to investigate and validate the measurement of physical activity in Avon Longitudinal Study of Parents and Children (ALSPAC) using the Actigraph accelerometer and to examine the early life (0-5 years) determinants of physical activity in ALSPAC among 11-12 year olds.

No description available.

Study 1: Aims: Compare the uniaxial MTI/CSA accelerometer and the biaxial Actiwatch accelerometer against direct observation of total physical activity and minute-by-minute physical activity in 3-4 year olds. Methods: MTI/CSA-7164 and Actiwatch accelerometers simultaneously measured activity during 35-45 minute sessions of structured play in 78, 3-4 year olds. Rank order correlations between accelerometry and direct observation were used to assess the ability of the accelerometers to assess total activity. Within-child minute-by-minute correlations were calculated between accelerometry output and direct observation. Results: For assessment of total activity MTI/CSA output was significantly positively correlated with direct observation (r 0.72, p<0.001), Actiwatch was not (r 0.16, p>0.05). Conclusion: The present study suggests that for epidemiological assessment of total physical activity in young children the MTI/CSA-7164 provides greater accuracy than the Actiwatch. Study 2: Aim: To cross-validate the 1100 counts/ minute cut-off for the assessment of sedentary behaviour in an independent sample of young children using the MTI/CSA accelerometer. Methods: A previously developed cut-off for MTI-CSA accelerometry output (validation study) in 30 healthy Scottish 3-4 year olds, was cross-validated against direct observation in an independent sample of (n = 52) healthy Scottish 3-4 year olds. Results: In the cross-validation study sensitivity was 83%: 438/528 inactive minutes were correctly classified. Specificity was 82%: 1251/1526 non-inactive minutes were correctly classified using this cut-off. Conclusion: Sedentary behaviour can be quantified objectively in young children using accelerometry.

Physical activity (PA) and reducing the time spent sedentary can favourably impact the health and wellbeing of preschool aged children. Despite the importance of regular P A, objective monitoring studies suggest that young children do not accumulate enough P A to benefit their health. Furthermore, relatively few interventions to promote PA in children under 5 have been rigorously evaluated and intervention studies to date have generated mixed results. The aims of this thesis were to a) assess within-day variability of objectively measured moderate-to- vigorous physical activity (MVP A) during weekdays and weekend days among preschool children; b) investigate the effect of a curricular Active Play intervention on children's sedentary and P A behaviours; and, c) investigate the effect of a family focused Active Play intervention on children's weekday and weekend day sedentary time and total P A. Study 1 Background: Identifying periods of the day which are susceptible to varying levels of P A may help identify key times to intervene and potentially change preschool children's PA behaviours. This study assessed variability of objectively measured MVP A during weekdays and weekend days among preschool children. Method: One hundred and eighty-eight children (aged 3-5 years; 53.2% boys) from a northwest English city wore uni-axial accelerometers for 7 consecutive days. Results: Higher levels of MVP A were recorded in boys, particularly those who attended preschool for a half day. Children who attended preschool for a full day engaged in 11.1 minutes less MVPA than children who attended for a half day. After-school hours were characterised by a decrease in activity for all groups. Patterns of activity during the weekend were smoother with less variability. Conclusion: This study identified discrete segments of the week, specifically afterschool and during the weekend, when preschoolers engage in low levels of PA. Higher levels of MVPA among children who attended preschool for less time each day suggests that the structured preschool environment is related to decreased activity. Consequently, there is a need for interventions in young children to focus on school and home environments. - Study 2 Background: Early childhood is a critical time for the promotion of healthy lifestyle behaviours such as physical activity. Cross-sectional studies suggest that preschool children are not sufficiently active to benefit their health. Few studies have investigated the effect of interventions on physical activity levels and time spent being sedentary in this population. The aim of this study was to investigate the effect of a school-based active play intervention on preschool children's physical activity and sedentary time. Method: Two hundred and forty children were recruited from 12 randomly selected preschools in the North West of England. Six schools were randomly assigned to either an intervention (n=6) or a current practice comparison group (n=6). One teacher in each intervention school received training in the delivery of a 6-week active play programme including active play resources. The training programme was delivered by experienced active play professionals. Comparison schools received the active play resources (but not the training) and were asked to deliver their usual active play provision. Children wore a uni-axial accelerometer for 7 days at baseline, post-test and at 6 months follow up. Whole week sedentary time and physical activity adjusted for pupil- and school- level covariates were analysed using multilevel analyses. Results: No significant intervention effects were observed for sedentary time or physical activity. Sex and hours spent at school were significant predictors of physical activity in this age group, with boys engaging in less sedentary time and more light intensity activity than girls. Children who spent fewer hours at school were significantly more active than those who spent more time at school. BMI, maternal education, child's ethnicity and accelerometer wear time were not associated with activity levels. Conclusion: Physical activity during intervention classes was high. However the six teacher training intervention sessions did not increase physical activity or decrease sedentary time over a week. Specific covariates were identified as having a significant effect on the outcome measures. Moreover, children who spend more time at pre-school were less active suggesting that this setting was not as conducive to physical activity engagement as other environments. Study 3 Background: Early childhood provides a window of opportunity for the promotion of physical activity. Given the limited effectiveness of interventions to date, new approaches are needed. Socio-ecological models suggest that involving parents as intervention targets may be effective in fostering healthier lifestyles in children. This study describes the effectiveness of a family-focused' Active Play' intervention in decreasing sedentary time and increasing total physical activity in preschool children. Method: Seventy-seven families were recruited from 8 randomly selected SureStart children's centres in the North West of England. Centres were randomly assigned to either an intervention (n=4) or a comparison group (n=4). Parents and children in the - intervention group received a IOeweek active play programme delivered by trained active play professionals; this included an activity and educational component. Families in the comparison group were asked to maintain their usual routine. Each participating parent and child wore a uni-axial accelerometer for 7 days at baseline and post-test. Week and weekend day sedentary time and total physical activity adjusted for child- and home- level covariates were analysed using multilevel analyses. Results: Significant intervention effects were observed for sedentary time and physical activity for both week and weekend days. Children in the intervention group engaged in 1.5% and 4.3% less sedentary time during week and weekend days, respectively and 4.5% and 13.1 % more physical activity during week and weekend days, respectively than children in the comparison group. Parent's participation in sport and their physical activity levels, child's sex, availability of media in the home and attendance at organised activities were significant predictors of sedentary time and physical activity in this age group. Conclusion: A 10-week family focused active play intervention produced positive changes in sedentary time and total physical activity levels in preschool children. Specific covariates were identified as having a significant effect on the outcome measures. Moreover, children whose parents were active engaged in less sedentary time and more physical activity suggesting that parent's activity habits are mediators of physical activity engagement in this age group.

The aim of this thesis was to investigate the impacts of physical activity (PA), cardiorespiratory fitness (CRF), body composition and lifestyle education on cardiometabolic (CM) risk in 10-11 year old children. This broad aim was approached using three studies. Studies 1 and 2 were cross sectional observational studies, and study 3 was a clustered randomised control trial, with intervention effects assessed at post intervention and again at 8 to 10 weeks after the intervention. Initially, in the first cross sectional study (Chapter 4) the relationships between non- invasive (LV Mass, E/A, E'/A', E/E', trunk fat mass, whole body fat mass) and invasive CM risk markers (CRP, HOMA-IR, adiponectin, TC: HDL-C), and between all risk markers and CRF (V02 peak), time spent sedentary, moderate to vigorous intensity PA (MVPA) and vigorous PA (VPA) were investigated in 10-11 year old children (n=62). The key findings were significant but generally weak relationships present between some of the non- invasive and invasive markers of CM risk and risk markers also had significant correlations with measures of CRF and PA. CRP was significantly positively correlated with whole body fat in boys (rho = 0.486, p < 0.05) and girls (rho = 0.485 , p < O.Ol) and with trunk fat mass in boys (rho = 0.384, p < 0.05) and girls (rho =0.489, p < O.Ol). Adiponectin was negatively correlated with whole body fat (rho = -0.446, p < 0.05, and R=-0.697, p < O.Ol) and trunk fat mass (rho = -0.614, p < O.Ol; rho = -0.475, p < O.Ol) in boys and girls respectively, and in girls adiponectin also correlated positively with E'/A' (r=0.356, p < 0.05). In boys only, TC:HDL-C was positively correlated with whole body fat (rho =0.407, p < 0.01) and trunk fat mass (rho =0.391, p < 0.05). ; V02Peakwas negatively correlated with CRPin boys (Rho = -0.492, p < 0.05) and HOMA-IR in girls (Rho =-0.522, p < 0.01). V02Peak was also negatively correlated with whole body fat (rho =-0.515, p < 0.01; r=-0.697, p < O.Ol) and trunk fat mass (rho=-0.494, p < 0.05; rho =-0.706, p < 0.01) in boys and girls respectively. Both MVPA and VPA correlated negatively with TC: HDL-C in girls (rho= -0.396, p < 0.05; rho =-0.428, p < 0.05) and MVPA correlated with whole body fat (rho= -0.602, p < O.Ol) and trunk fat mass (rho=-0.65, p < 0.01) in boys. VPA also correlated with whole body fat in girls (rho= - 0.544, p < O.Ol) and with trunk fat mass in both boys (rho= -0.428, p < 0.05) and girls (rho= - 0.468, p < 0.01). Time spent sedentary had a positive correlation with whole body fat in boys (rho = 0.429, p < 0.05). This study demonstrated that risk factors clustered in individuals and that relationships were present between invasive and non-invasive markers of cardiometabolic risk, and provided preliminary evidence to investigate this phenomenon further. The correlations described in this study suggest a clustered risk score which includes both invasive and non-invasive measures may add value to predicting overall risk. The second cross sectional study (Chapter 5) investigated clustered CM risk, by combining invasive markers with non-invasive 'pre-clinical' markers of CM risk into a clustered risk score, in a different cohort of 10 - 11 year old children. Clustered risk scores were negatively correlated with CRFand PA. V02 peakshowed a moderate negative correlation with CRSA (r=-0.57, p < 0.01) and CRS B (r= -0.60, p < O.Ol) VPA showed a moderate negative correlation with CRSA (r= -0.51, p= 0.01) and CRSB (r= -0.50, p=O.Ol). MVPA showed a moderate negative correlation with CRSA (r= -0.44, p= 0.03) and CRSB (r= -0.41, p=0.04). Sedentary time showed a moderate positive correlatcorrelation with CRSA (r= 0.414, p= 0.049). The evidence provided by these two observational studies, Study 1 (Chapter 4) and Study 2 (Chapter 5), along with other literature, as discussed throughout this thesis, gave rationale for an intervention with the aim to reduce negative lifestyle behaviours, of low levels of PA, high levels of sedentary behaviour and poor nutritional balance, increase CRF and maintain a healthy body weight.

No description available.