Studies of the "activitystat" hypothesis Public Deposited

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  • March 22, 2019
Creator
  • Baggett, Christopher David
    • Affiliation: Gillings School of Global Public Health, Department of Epidemiology
Abstract
  • This dissertation explored the potential existence of an "activitystat:" a biologically controlled regulatory mechanism for physical activity. This was accomplished through two studies of participants in the Trial of Activity for Adolescent Girls (TAAG). The first study examined the tracking of physical activity over a two-year time period. In the second study we investigated the associations between physical activity and inactivity. It has been suggested that tracking, or stability, of physical activity levels over time is indication that an "activitystat" exists. That is, despite changes in social and environmental influences on physical activity over time, an individual's relative rank of physical activity within a group remains consistent. TAAG provided a unique opportunity to examine tracking since it included both an objective and subjective measure of inactivity and physical activity. In 951 participants who were measured in 6th grade and two years later in 8th grade, tracking of inactivity, moderate-to-vigorous physical activity, and vigorous physical activity was fair-to-moderate. Objectively measured tracking tended to be higher than that from self-reported inactivity and physical activity. These results cast some doubt on the "activitystat" hypothesis as they suggest that physical activity and inactivity habits are dynamic for most girls during early adolescence. The "activitystat" hypothesis also posits that increases in moderate-to-vigorous physical activity are accompanied by a compensatory reduction in light physical activity and an increase in inactivity in order to maintain a consistent total physical activity level from day to day. In 6,916 8th grade TAAG participants we found no associations over 6 days of measurement between physical activity and inactivity that would suggest compensatory changes occur that would result in the maintenance of total physical activity levels. As girls increased their inactivity total physical activity decreased, as moderate-to-vigorous physical activity increased inactivity decreased, and as moderate-to-vigorous physical activity increased light physical activity increased. This dissertation failed to find support for the "activitystat" hypothesis. These findings may indicate that well-designed physical activity interventions for adolescent girls should be able to produce positive results through either increasing physical activity or decreasing inactivity.
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  • In Copyright
Advisor
  • Stevens, June Sheppa
Degree granting institution
  • University of North Carolina at Chapel Hill
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