Psychological well-being occurs when there is an absence of mental disorders and presence of positive states. Given the increasing prevalence of mental disorders, which are thought to have their roots in childhood, improving psychological well-being in children is currently an important area of research. Physical activity has been proposed as a method by which negative states can be reduced and positive states increased, thereby increasing children’s overall psychological well-being and in turn helping to protect against a decline into clinical disorders. Research focusing on physical activity and psychological well-being has mainly used self- reported measurements to assess physical activity, a method which leads to considerable non-differential misclassification that in turn will attenuate associations between physical activity and psychological wellbeing. Few studies have employed more precise, objective measures such as accelerometry. Despite providing a more precise measure of physical activity, a number of limitations are present with the use of accelerometry, specifically concerning the data reduction processes. Various decisions made when handling accelerometer data can result in misclassification of time spent in different intensities of physical activity and can introduce selection bias. The present thesis aims to address how the decisions made during data reduction can affect estimates of physical activity prevalence and alter the observed relationships between physical activity and psychological well-being in children. The first study of this thesis assessed the misclassification of activity intensities occurring as a result of the use of various accelerometer cut-points and the resulting variation in relationships between physical activity and psychological well-being that occurs. Results showed that the use of different cut-points to determine physical activity intensity alters the magnitude of the relationship between physical activity and psychological well-being; relationships were attenuated, with some becoming non-significant. The second study addressed the issue of children’s compliance with wear time requirements over multiple time points; compliance with wear time decreased over time, whilst inclusion and exclusion rules based on minimum wear times introduced selection bias. The use of more lenient wear time criteria, to reduce selection bias, introduced misclassification of physical activity intensities. Further, longitudinal relationships between physical activity and psychological well-being differed depending upon the wear time criteria employed. The third study aimed to address whether compliance, and in turn selection bias would systematically differ between groups of a trial of a physical activity intervention, and whether this would alter the results of the intervention itself. Results showed that compliance varied across trial condition, that selection bias with groups was different for each condition and that non-compliance hindered the exploration of the mediating effect of physical activity on psychological well-being. Study four involved the validation and calibration of a new wrist worn, waterproof physical activity monitor more compatible with 24 hour wear, thus potentially overcoming the compliance problems noted in the earlier studies. Results showed good concurrent and criterion validity, with high classification accuracy for the cut-points created. The final study assessed the acceptability and compliance with 24 hour wear in children and allowed a detailed examination of the underestimation of time spent in PA intensities that occurs from capturing shorter and different periods of the day. Results showed large misclassification with 10 hour capture periods relative to complete observation, with time in activity intensities varying across different periods of the day. The results of this thesis demonstrate that substantial selection bias and misclassification of time in activity intensities can be introduced through the decisions made during the processing of raw accelerometry data. Furthermore, this error alters the relationships between physical activity and psychological well-being. The results indicate that the true relationship between physical activity and psychological well-being in children may still be unknown, with researchers reporting relationships and effects only relevant to the measurement methods and data reduction processes they have employed. A method of overcoming selection bias and reducing misclassification is through 24 hour wear, which through the design of new accelerometers is now possible. Future studies should use monitors compatible with and acceptable for complete observation. This would result in more precise estimates of time spent in physical activity intensities and less selection bias. Both of these improvements would greatly increase our understanding of the relationship between physical activity and psychological well-being in children.

While the health benefits of physical activity are commonly recognised, increasing evidence indicates that significant percentages of children, particularly girls, are not sufficiently physically active. Children spend a large proportion of their waking day at school; however their opportunities to be physically active during the school day, beyond the traditional PE lesson and break times, are limited. Increasing children’s levels of physical activity during their time at school may be a key approach to increasing children’s overall levels of physical activity. The aim of this study was to evaluate the outdoor education programme ‘Forest School’ as a source of school based physical activity. A review of existing research showed that there had been no rigorous evaluation of physical activity during Forest School sessions. A two phase mixed method design was used. The first phase used a repeated measures controlled design to objectively measure the amount, intensity, duration and frequency of the participants’ (n26 age 9-10) physical activity during Forest School. The second phase used semi-structured paired interviews (n24 age 10-11) to understand the subjective experience of the Forest School physical activity. The study was conducted in the central belt of Scotland. The results showed that during Forest School sessions the participants engaged in a significantly greater total amount of physical activity, at a higher intensity, and with a greater frequency of longer bouts, in comparison to the typical school days. The children were also shown to reach the recommended hour of MVPA during the Forest School sessions. The children reported enjoying and appreciating the opportunity to be physically active in an environment they had little previous experience of using. Existing barriers to physical activity in other contexts, in particular bad weather and low motivation, did not appear to be relevant at Forest School. The inequality in levels of physical activity and motivation to be physically active, between males and females, was shown to typically be lower on the Forest School days. The findings suggest participation in Forest School resulted in greater quantities of inclusive and enjoyable physical activity at higher intensities than otherwise experienced at school.

Background: The first five years of life, called the early years is a period of rapid and vital physical, behavioural, emotional and social development. Physical activity (PA) is one of the behaviours which develop during the early years, and high levels of PA during the early years have been shown to be related to multiple health outcomes. The importance of PA of young children (children during the early years) has been highlighted by a number of national governments. In order to better inform future interventions and public health policies, a greater understanding of the correlates and determinants of young children s PA is vital. Previous research has been limited through measurement inconsistencies, and few studies have been conducted within multi-ethnic communities, where many young children in the United Kingdom are born. Thesis Aims: 1) to systematically review published research in order to establish currently known correlates and determinants of PA in the early years and identify gaps within the literature. 2) Calculate an accelerometer wear-time criteria to reliably measure young children s habitual PA. 3) Investigate the validity and test re-test reliability of a new parental proxy reported PA questionnaire. 4) Investigate the levels and correlates of moderate-to-vigorous PA (MVPA) in toddlers (1-3 year olds) from a predominately bi-ethnic and bi-linguistic population. Methods: Aim 1) nine electronic databases were searched to identify previous research which investigated associations between an exposure/variable, and a quantitative measure of PA. Correlates/determinants of total PA (TPA), MVPA and light-intensity PA (LPA) were reported using an ecologic model. Aim 2) to calculate a wear-time criteria for young children a simple stepped process was used whereby statistical tests were run to determine the minimum length of wear for one day, if there were any differences between weekdays and weekend days, and the presence of reactivity. Intra-class correlation models and the Spearman-Brown prophecy formula were used to calculate wear-time reliability. Aim 3) this study was undertaken by 196 parents completing a proxy report questionnaire on their child s PA and sedentary behaviour after seven days of their young child (mean age 3.2 ,SD: 0.8 years) wearing an accelerometer. A total of 156 (79.6%) questionnaires were completed in English and 40 (20.4%) were completed in transliterated Urdu. Of the 196 parents, 109 parents completed the EY-PAQ a second time seven days apart from the first EY-PAQ completion; this was to assess test re-test reliability of MVPA and sedentary time. Validity analysis used all data and data falling with specific proportion boundaries for MVPA (2%-41%) and sedentary time (30%-94%). Reliability was assessed using intra-class correlations (ICC) and validity by Bland Altman plots and rank correlation coefficients. Aim 4) this study was undertaken by conducting a cross-sectional analysis using 24 month olds and their mothers data collected as part of the Born in Bradford (BiB) birth cohort sub-sample study called BiB1000. The outcome variable was daily minutes of MVPA measured by the EY-PAQ. Numerous independent variables covering the layers of an ecological model were selected. Univariate linear regression models accounting for sex, age, language and season were conducted to examine the differences between White British and South Asian children s daily minutes of MVPA and each of the EY-PAQ s domains, and the proportion of time spent in MVPA within each of the EY-PAQ s domains. A series of univariate linear regression analyses were performed to examine and identify correlates of MVPA (for the whole sample, and separately for White British and South Asian children). Significant variables found in univariate analyses were then included in hierarchical multivariable regression models (based upon the ecological model), in order to examine the percentage of variance accounted for in daily minutes of MVPA. Results: Aim 1) The systematic review identified a large volume of published research. All studies took place in high income countries and few studies (6%) were of high quality. A small number of correlates and determinants of TPA were identified. The only correlate of MVPA was sex and no determinants of MVPA or LPA were found. PA correlates/ determinants were relatively consistent between objective and subjective PA measures and few studies investigated correlates of toddlers or between children with White and South Asian ethnicity. Aim 2) No differences in accelerometer-determined time in TPA, MVPA or sedentary time were observed between weekdays and weekend days within this sample of young children. Similarly, there was no evidence of reactivity to accelerometer use. For young children living in Bradford, an accelerometer wear-time of a minimum of six hours on any three days was shown to provide reliable estimates of accelerometer-determined time in TPA, MVPA, and sedentary time. Aim 3) The test re-test reliability of the EY-PAQ was moderate for sedentary time and fair for MVPA. The EY-PAQ had poor agreement with accelerometry with both sedentary time and MVPA before the application of boundaries. Post application of boundaries the EY-PAQ still had poor agreement with accelerometer-determined sedentary time but good agreement for MVPA. Limits of agreement were wide for all variables and language and ethnicity did not confound results. Aim 4) Bradford toddlers were found to be very active and no difference was observed between proxy-reported time spent in MVPA between White British and South Asian children. However, White British toddlers were found to have spent significantly more time in reported MVPA while walking for transport compared to South Asian toddlers; while South Asian toddlers reportedly spent significantly more time of MVPA in the home compared to White British toddlers. Correlate models were only statistically significant when multi-layers of the ecological model were included; and correlates differed for South Asian and White British children. Conclusions: There is a need for more high-quality studies exploring correlates/determinants across all layers of the ecologic model, and research investigating MVPA correlates/determinants of toddlers and between ethnicities is sparse. The work reported within this thesis has produced a reliable wear-time criterion for use to estimate accelerometer-determined PA and sedentary time in young children living in a bi-ethnic community. This criterion can now be used in future accelerometer studies (validation, observational and intervention) and the stepped-process offers researchers a method to derive sample-specific wear time criteria. The EY-PAQ is a promising habitual population-level measure of young children s MVPA from a bi-ethnic community. In situations when objective methods are not possible for measurement of young children s MVPA, the EY-PAQ may be a suitable alternative. Levels of toddlers MVPA did not differ by ethnicity but the contexts and correlates did. Therefore, future interventions should seek to maintain and maximise high levels of toddlers MVPA and tailor interventions by ethnicity. The research conducted within this thesis will inform the development of surveillance systems, interventions and public health polices to improve young children s PA levels, particularly children living in a bi-ethnic community.

Previous reports have demonstrated that children’s physical activity is typically intermittent in nature. Accelerometers are reliable and valid tools for quantifying the pattern of activity in children. However, in order to interpret accelerometer output it is necessary to apply appropriate accelerometer thresholds for classifying physical activity intensity. Currently multiple accelerometer thresholds are available in the literature and it is unclear which are the most appropriate or whether thresholds should be sample specific. Additionally, there is little information regarding how the pattern of activity in children varies across groups and how activity patterns relate to health. The overall aim of the thesis was to describe the pattern of habitual physical activity, using objectively-measured physical activity data, in relation to health outcomes in pre-adolescent boys. The first objective was to characterize the pattern of boys’ habitual physical activity, using objectively-measured physical activity data. The second objective was to investigate the relationship between habitual physical activity and specific aspects of the activity pattern and health outcomes in boys. The final objective was to investigate the effects of continuously- versus intermittently- accumulated physical activity on acute health outcomes in boys, using an intermittent activity protocol based on the measured pattern of habitual activity in boys. The first four studies used a sample of 54 boys, aged 8 to 10 years. The final study used a different sample of 10 boys, aged 9 to 11 years. Both samples were from the county of Devon, UK. The first study of this thesis established sample-specific accelerometer-intensity thresholds through calibration research with ActiGraph accelerometers (counts•2s-1) in boys. The second study in the thesis demonstrated that relationships between time accumulated at different activity intensities and health (fatness, peak oxygen consumption and resting blood pressure) in boys were similar irrespective of whether sample-specific or published thresholds were employed as long as the threshold was at least equivalent to a brisk walk (i.e. >4 METs). However, the prevalence of children reported as meeting activity guidelines did differ according to thresholds employed. Study three showed that, despite little difference between overweight and normal weight boys in overall activity, time spent sedentary and minutes of light, moderate and vigorous intensity activity accumulated, aspects of the activity pattern (frequency, intensity and duration of ≥4 s (short) and ≥5-min (long) bouts of ≥light, ≥moderate, ≥vigorous and ≥hard intensity activity) differed by weight status. Overweight boys accumulated fewer and shorter bouts of activity, particularly sustained bouts of activity which were of moderate intensity or greater. Study four examined the relationship between activity pattern and health in boys further, focusing on body fatness, aerobic fitness, blood pressure and microvascular function. Results demonstrated that summary measures of activity were negatively related to body fatness, and positively related with both aerobic fitness (i.e., total, moderate, vigorous and hard activity) and endothelial function (i.e., total and light activity). Time spent sedentary was negatively related to endothelial function. The frequency and duration of activity bouts of ≥moderate intensity and the intensity of all activity bouts (i.e., ≥light intensity) were most important for body fatness and aerobic fitness. The frequency of all bouts (short and long) of at least light intensity was most important for endothelial health. Finally, study five moved away from chronic measures of health and examined the acute physiological effects of the recommended daily amount of physical activity (60 minutes of physical activity of ≥moderate intensity) on postprandial lipaemia and microvascular function in boys the following day. Furthermore, the study aimed to assess whether the effects differed depending on whether the activity was accumulated continuously or in a manner more similar to the children’s typical activity patterns identified in studies 3 and 4. In contrast to findings from adolescents and adults, 60 minutes of >moderate intensity activity did not impact on postprandial lipaemia or microvascular function the following day in healthy, active boys, regardless of how it was accumulated. The results of the present thesis indicate that aspects of the activity pattern are significantly related to health in boys and differ according to type of day and weight status. Furthermore, the benefits of sporadically-accumulated activity are equally as strong as continuously-accumulated activity to body fatness, aerobic fitness and endothelial health in boys. Since children typically accumulate short, intermittent bouts of activity, the promotion of sporadic activity (i.e., in intervention research and current physical activity guidelines for children and youth) might increase enjoyment and adherence. The benefits of acute intermittent exercise (which simulates free-living activity) on postprandial lipaemia and microvascular function in inactive children with risk factors for cardiovascular disease should be investigated. Longitudinal investigations into the activity pattern of a much larger and more age-diverse sample of boys and girls are needed to determine whether any changes in aspects of the activity pattern might alter these and other health outcomes (i.e., cardiovascular risk factors).

Im Vergleich zu den traditionellen Risikofaktoren wurde die Bedeutung körperlicher Aktivität für die primäre und sekundäre Prävention der koronaren Herzerkrankung nur ungenügend berücksichtigt. Insbesondere bei Jugendlichen hat sich in den letzten Jahren eine deutliche Abnahme an körperlicher Aktivität verbunden mit einer gleichzeitigen Zunahme des Übergewichtes bemerkbar gemacht. Inzwischen gelten bis zu 25% der Schulkinder in Europa als übergewichtig, der Trend ist weiter steigend. Als einer der wichtigsten Ursachen für diese Entwicklung wird die Abnahme der körperlichen Aktivität diskutiert. Körperliches Training ist einer der Hauptpfeiler der Primär- und Sekundärprävention bei Patienten mit kardiovaskulären Erkrankungen. Die protektive Wirkung auf das kardiovaskuläre System und die prognostische Bedeutung körperlicher Aktivität wurde in großen Kohortenstudien überzeugend dokumentiert und die zugrunde liegenden Mechanismen sind zumindest teilweise aufgeklärt. Bei erwachsenen und älteren Menschen ist die Bereitschaft körperlich aktiv zu sein jedoch gering und nimmt mit zunehmendem Alter ab. Um ein hohes Niveau körperlicher Aktivität lebenslang zu erhalten, muss bei Kindern und Jugendlichen begonnen werden, diesen Lebensstil zu erzeugen und zu pflegen. Ziel des Leipziger Schulprojektes ist es, durch gezieltes körperliches Ausdauertraining im Rahmen eines täglichen Sportunterrichts in Verbindung mit Unterrichtsstunden zur gesunden Lebensführung eine Steigerung der körperlichen Aktivität (gemessen anhand der maximalen Sauerstoffaufnahme VO2 max) der Schulkinder zu erreichen. Des Weiteren sollen als sekundäre Studienvariablen der Einfluss täglichen intensivierten Sportunterrichts auf das atherogene Risikoprofil gemessen und anhand verschiedener Parameter untersucht werden. Zusammen mit der sportwissenschaftlichen Fakultät (Frau Prof. Alfermann) werden zudem psychosoziale Aspekte analysiert. Das Leipziger Schulprojekt wurde 2005 an 3 Schulen begonnen. In diesem Pilotprojekt sollte zudem geprüft werden, inwieweit ein Interventionsprogramm mit täglichem Sportunterricht in den Schulen etabliert werden kann. Die Effizienz dieses Projektes sollte ebenfalls nach einem Jahr durch Erfassung verschiedener Parameter überprüft werden.

Abstract Aim The aim of this study was to describe levels and patterns of three-year-old children´s physical activity. Furthermore, to investigate if there were any weight status-, gender- and parental SES differences in three-year-old children’s physical activity levels, using objective and subjective measurements from Early Stockholm Obesity Prevention Project (Early STOPP). Methods Data from 93 children, three years of age, included in the Early STOPP study was used. Children wore an actigraph GT3X+ accelerometer for at least four consecutive days including one weekend day. Average activity in counts per minute (CPM), time spent in sedentary, light PA and moderate to vigorous physical activity (MVPA) was assessed (5 s epoch) and used to examine differences between gender, weight status (ISOBMI according to Cole et al) and socioeconomic status (SES). For this reason an index measuring SES was created using subjective data; parental reported information on living conditions and background characteristics, from the Early STOPP study. Differences between weekdays and weekend days was also examined.    Results The result showed neither any differences in PA between gender nor weight status and no differences between SES-groups. There was a difference in PA levels between weekdays and weekend days and a difference in PA between housing types. The children spent more time being active on weekdays and children living in apartments were more active than children living in villas. Children spent approximately 67% of their time being sedentary and an average of 12,5 minutes in MVPA. Conclusion The study concludes that PA-levels in children three years of age are low. There was a difference between housings, suggesting that parents/guardians play an important role in young children’s PA. However more research is needed to fully understand the PA-behavior of young children and their parents. The absence of PA differences between genders implies that gender differences later in childhood is an effect of social structures rather than innate differences. Objectively measured PA on children at this age is rare and therefore this study contributes to the knowledge regarding young children’s PA-behavior. Furthermore there is also a need to establish agreed upon definitions for SES and of thresholds to use when examining PA with accelerometer. / Sammanfattning Syfte Syftet med denna studie var att beskriva tre år gamla barns fysiska aktivitetsmönster och nivåer. Samt att undersöka om det fanns några skillnader i fysisk aktivitet (FA) beroende på viktstatus, kön och socioekonomisk tillhörighet genom objektiva och subjektiva mått från Early Stockholm Obesity Prevention Project (Early STOPP). Metod Data från 93 treåriga barn inkluderade I Early STOPP studien användes. Barnen använde en Actigraph GT3X+ rörelsemätare under minst fyra sammanhängande dagar med minst en helgdag. Genomsnittlig FA i slag per minut (CPM), tid i stillasittande, lätt aktivitet samt måttlig till kraftig fysisk aktivitet (MVPA) bedömdes (5 s intervaller) och användes för att undersöka om det fanns skillnader mellan kön, viktstatus (ISOBMI enligt Cole et al) samt socioekonomisk status (SES). Av denna anledning skapades ett index för SES med hjälp av subjektiva data; föräldrarapporterad information kring bakgrund och levnadsförhållanden från Early STOPP-studien. Även skillnader i FA mellan vardagar och helger undersöktes. Resultat Resultaten visade inga skillnader i FA mellan könen, viktstatus eller socioekonomisk tillhörighet. Det fanns däremot en skillnad mellan veckodagar och helger samt mellan boendeformer. Barnen var mer aktiva under veckodagarna och barnen boende i lägenhet var mer aktiva än barnen boende i villa. Ca 67 % av tiden spenderades i stillasittande och ungefär 12,5 min per dag spenderades i MVPA. Slutsats Studien drar slutsatsen att aktivitetsnivån hos tre år gamla barn är låg. Det fanns en skillnad i FA mellan boendeformer vilket indikerar att föräldrar/vårdnadshavare spelar en viktig roll för små barns aktivitet. Dock behövs mer forskning för att till fullo förstå barn och föräldrars aktivitetsmönster och hur dessa samvarierar. Avsaknaden av skillnader i FA mellan könen indikerar att könsskillnader senare i barndomen är en effekt av sociala strukturer snarare än medfödda skillnader. Objektivt uppmätt fysisk aktivitet hos barn i den här åldern är ovanligt och därför bidrar denna studie med kunskap kring små barns FA. Avslutningsvis drar denna studie slutsatsen att det finns ett behov av internationella bestämmelser kring definitioner av SES och av tröskelvärden att använda när FA mäts med accelerometri.