Adolescence is a period of dynamic behavioural and emotional development that can increase young people's vulnerability to mental health problems. With 70% of mental disorders having their onset during childhood or adolescence, identifying modifiable factors of these disorders among adolescents can help inform future interventions aiming to improve mental health. One of these factors is electronic technology which has become pervasive in our modern society, occupying an important portion of young people's days and changing their lifestyle. This has created serious concerns regarding the impact of heavy recreational screen use on adolescents' health, especially with the vast majority exceeding the sedentary recreational screen time recommendations of 2 hours or less per day. Evidence suggests that screen time can be associated with adolescent mental health problems. However, little is known about how the extent, nature, and types of recreational screen engagement among adolescents are associated with mental health problems as the body of evidence is very mixed, and many questions remain unanswered. Accordingly, the aims of this dissertation were: i) to summarize the evidence regarding correlates of sedentary screen pursuits among youth, ii) to examine how different types of screens, incorporating their newer forms, are associated with adolescents' mental health cross-sectionally and longitudinally, iii) to examine the nature of screen use and its association with suicidal behaviours; and iv) to explore the moderating role of sex, age, and parental support in the association between screen time and different mental health problems. To achieve these objectives, we completed four manuscripts, all prepared for submission to peer-reviewed scientific journals: 1. A narrative review on the psychological correlates of sedentary screen time behaviour among children and adolescents. 2. Heavy social media use and psychological distress among adolescents: the moderating role of sex, age, and parental support. 3. Problematic technology use, suicidal ideation, and suicide attempt among adolescents: the moderating role of sex. 4. Longitudinal associations between different types of screen use and depression and anxiety symptoms in adolescents. Collectively, our results identified that high levels of sedentary screen behaviour are associated with more severe anxiety, depressive symptoms, and suicidality among adolescents. However, the strength of associations varied between some screen types. Additionally, the findings of this dissertation indicate that a further increase in screen time is associated with increased mental health problems. Lastly, an important role of sex and age in this association was identified. These results can be used to inform future research in this field and guide future interventions designed to manage screen use among adolescents and improve their mental health.

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Energy cost of walking at any given speed is higher for heavier people than for lighter ones. We compared adolescents that were matched for total body mass but had different body composition. Nine pairs of boys (16.37 ± 1.57 years in the lean group and 12.90 ± 1.49 years in the obese group) participated. Metabolic energy expenditure (EE) was compared at three walking speeds and moments and powers at the hip and ankle at push off were analyzed. Assessment of fat mass and distribution was performed using whole body dualenergy x-ray absorptiometry. A repeated measure ANOVA was performed when matched pairs were compared. Based on multiple regression, pooling all subjects together, body mass was the main predictor of EE. Variance explained by adiposity increased with increasing speed. Obese subjects tended to expend more energy than their lean pairs at the two fastest walking speeds (5 and 6kph). There was a significant difference between the pairs in EE (kJ/min) at 6kph (p<0.05). Ventilation showed the same pattern as V02net (exercise V02 minus resting V02), increasing with increasing speed and showing differences between the pairs at the fastest speed. Heart rate was consistently higher in the obese subjects. Stride length, stride rate, progression velocity and moments and powers at the hip and ankle at push off were not correlated with body fat. No relationship between V02net. total amount of body fat, or segment fat content was found. Total amount of fat in the body and the amount of fat in the legs had no influence on gait parameters. In conclusion, excess body fat does not influence the energy cost of walking at low speeds but does so at 6kph. Obese subjects demonstrated higher effort at all speeds. Amount of fat distributed in body segments does not influence either energy cost of walking or mechanical gait parameters. / Thesis / Master of Science (MSc)

Participating in organized sports activities can result in developmental benefits to the adolescent. Increased fitness, self-esteem, competency, academic success and increased recognition by peers are few of the benefits cited by researchers. Participation can also provide opportunities for developmental liabilities to occur. Researchers have cited liabilities such as stress, anxiety and physiological injury. Developmental benefits and liabilities have been the foci of the controversy that has existed over adolescents participating in interscholastic sports programs in the middle and junior high school. Although research has studied the impact of interscholastic sports on the high school and collegiate athlete, few studies have investigated the impact of interscholastic sports on the middle school athlete. This qualitative case study of four middle school athletes investigated the benefits and liabilities of participating on an interscholastic team to the adolescent athlete. Based on the literature, four domains were identified as benefits and two domains were identified as liabilities. These six domains were achievement, competency, fitness, self-esteem, sports injuries, stress and anxiety. Interviews were held with students, coaches and parents. These interviews were based on domain specific questions. A journal was kept, and a document review of achievement, attendance and medical records was completed. The study revealed a pattern of improved grades, increased skill levels in the sport, improved fitness, and increased self-esteem. The students experienced injuries and moments of stress and anxiety. / Ed. D.

Adherence to treatment recommendations following medical care for pediatric conditions is critically important for promoting optimal physical and psychological well-being. While it has been a focus of many studies across pediatric chronic illness populations, there is a dearth of research examining adherence following pediatric unintentional injury. Empirical evidence from studies with pediatric chronic illness samples indicates that youth experience a number of barriers to adherence to medical recommendations. Adherence is especially difficult for adolescents due to the unique challenges of this developmental period. A mixed methods research approach was utilized to gain a holistic understanding of potential psychological barriers to adherence following adolescent injury. Quantitative analyses examined the potential predictive roles of adolescent psychological [i.e., posttraumatic stress (PTSD), depression, quality of life] and relational (i.e., parent PTSD and depression) factors on adherence. Results of analyses were insignificant; thus, qualitative data was collected to deepen the understanding of barriers to adherence. Findings from qualitative data analyses suggested that a number of barriers to adherence to treatment recommendations exist, including: concern of pain medication addiction, competing activities, treatment side effects, health status, desire for autonomy, and symptoms of depression. Results of qualitative analyses also revealed the presence of additional factors that could facilitate adherence to treatment recommendations. Taking into consideration findings from both quantitative and qualitative analyses, adherence may be best conceptualized as a result of a dynamic decision-making process influenced by numerous interacting factors. This study is the first to examine barriers to adherence among adolescents following unintentional injury and provides an initial roadmap for understanding the mechanisms involved in this complex process. / Ph. D.

Since the 1990s, medical and media articles containing the word "obesity" inevitably included the word "epidemic" as well. These articles usually pointed to the exponential growth in overweight and obese persons in high-income and low-income countries alike. A recent field of literature called "fat studies" has sought to question this so-called epidemic, bringing to light inconsistencies or down-right falsehoods present in obesity research. While researchers in this field have importantly uncovered many myths surrounding obesity and overweight, examinations of the rhetorical strategies used to approve potentially dangerous weight loss or weight maintenance procedures remain few. This thesis project hopes to cover just a portion of that gap by examining two groups targeted most directly by obesity researchers: women and children. Particularly, this research examines potentially dangerous recommendations made by doctors and the media to pregnant obese women and obese adolescents. Ultimately, this project uncovers dualisms of wrong versus right bodies and fat stigmatization in the "objective" language of health about obesity. This polemic leaves pregnant women and adolescents little choice except either to conform or to face a world of media and medicine that blames these two groups for the "choice" to remain fat. / Master of Arts

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Th. Etat--Psychologie clinique--Paris 5--René Descartes, 1999. / Bibliogr. p. 434-447.