Abstract:
Adolescence is a high-risk period for physical inactivity as well as depressed affect, both related to various short-, mid-, and long-term negative consequences for adolescents' physical and mental health. Therefore, this developmental period is ideally suited for studying the association between change processes of everyday physical activity and change processes of depressed affect within person by applying an intensive longitudinal design. Given that physical activity substantially decreases during adolescence, researchers are working hard to better understand what actually impedes adolescents' physical activity participation. The present dissertation is based on three manuscripts and focuses on the nature and many facets of adolescents' barriers to physical activity, culminating in the development of a valid questionnaire for measuring multiple dimensions of barriers that can impede adolescents' physical activity participation most. Moreover, this dissertation aims to examine the within-person association between adolescents' daily everyday physical activity and depressed affect among adolescents with varying levels of vulnerability for elevated depressed affect (e.g., hyperactivity). Deeper insight into adolescents' barriers to physical activity and the temporal within-person associations between their everyday physical activity and depressed affect seems to be an important prerequisite for developing targeted, tailored interventions that enable adolescents to manage their most impeding barriers to physical activity in order to increase their physical activity and, thereby, reduce their depressed affect. However, despite the apparent relevance of both re-search topics for adolescents' general physical and mental health, data are still sparse. The aim of this dissertation is to make a contribution towards narrowing these research gaps.
Manuscript I addresses barriers to adolescents' physical activity. To date, this is the only publication that investigates the dimensional structure of barriers to physical activity in adolescents by applying both a qualitative and a quantitative approach. In Study 1 (qualitative study, item development), adolescents self-generate those barriers that impede their everyday physical activity most. Based on the categorization of 602 barrier items by two coders, 46 most commonly cited barriers to physical activity that should cover a broad range are selected for Study 2. In Study 2 (quantitative study, questionnaire validation), as a first step, we con-duct an exploratory factor analysis (EFA) using Mplus which provides the opportunity to interpret EFA results by means of established continuous fit indices (χ2, CFI, RMSEA, and SRMR). Item selection (25 out of 46 items) is based on these EFA results. A seven-factor model (leisure activities, lack of motivation, screen-based sedentary behavior, depressed mood, physical health, school workload, and preconditions) is the first model that shows an acceptable fit in all indices. As a second step, we conduct a confirmatory factor analysis (CFA) to test the seven-factor solution of the EFA and evaluate the model fit by using the χ2 test, CFI, RMSEA, and SRMR. Taken together, results indicate that a multidimensional approach for measuring adolescents' barriers to physical activity is valid within our sample and is more appropriate than uni- or two-dimensional approaches, which were predominately applied in prior research.
Study 1 of Manuscript II focuses on the within-person association between everyday physical activity (steps per day measured through pedometers) and same-evening depressed affect among adolescents and examines, as one of very few studies, whether higher levels of hyperactivity moderate this link. Results show that on days with higher-than-usual physical activity (i.e., more steps per day) adolescents experience less evening depressed affect than on days with lower-than-usual physical activity. As expected, this within-person physical activity–depressed affect link is stronger in adolescents with higher levels of hyperactivity. On a given day, with a 1-unit increase in physical activity (i.e., an additional 10,000 steps taken per day) above the within-person mean, adolescents' depressed affect decreased to almost zero ("not at all").
Manuscript III targets the within-person association between everyday physical activity (determined by minutes spent with moderate-to-vigorous physical activity (MVPA), per day measured by accelerometers) and next-morning and same-evening depressed affect among adolescents and, thus, supplements Study 1 of Manuscript II. However, Manuscript III exceeds Manuscript II with respect to sample size, measurement of physical activity (accelerometers instead of pedometers) and frequency of assessing depressed affect (twice instead of once per day). Moreover, as opposed to Manuscript II, Manuscript III investigates gender and day of the week (i.e., weekday versus weekend day) as moderators of the within-person link. Results indicate that for young women on weekdays, a 60-minute increase in MVPA above the within-person mean predicts a 50% decrease in next-morning depressed affect. There is no such time-lagged predictive relationship regarding MVPA on weekend days or among young men. Moreover, there was no within-person association between MVPA and evening depressed affect (same-day link).
Based on the results of the three manuscripts, the present dissertation highlights the importance of (a) considering multiple, diverse barriers to physical activity relevant to adolescents in health research and practice (with respect to the development and improvement of targeted intervention strategies to enhance adolescents' physical activity) and (b) systematically examining naturally occurring time-lagged or same-day change processes under everyday conditions to gain a better understanding of the association between adolescents' physical activity and depressed affect within person. In addition, results from Manuscripts II and III illustrate the great potential of everyday physical activity for alleviating depressed affect among adolescents on a day-to-day basis. However, further research is needed to replicate the results of this dissertation.
physical activity