Date of Award

8-9-2014

Document Type

Open Access Dissertation

Department

Exercise Science

First Advisor

Steven N. Blair

Abstract

Most physical activity research to date narrows its focus toward intensities and durations only encompassed in the Physical Activity Guidelines of moderate to vigorous intensity in at least 10 minute bouts (MVPA-10). Examining activity in this manner excludes light activity and shorter bouts, sometimes referred to as baseline physical activity (BPA) as it consists of the activity accumulated during daily life at durations and/or intensities below what is recommended. This dissertation provides an evaluation of the entire spectrum of physical activity (PA). Physical activity was studied in a unique way by looking at MVPA-10, then adding shorter bouts and light intensity to see if these additions further influence study outcomes. This dissertation incorporated this concept into the analyses while linking behavioral investigations of physical activity to a physiological investigation of how such activity influences adiposity and weight. Thus, it transitioned from what characteristics influence physical activity behavior to how physical activity influences health. Three separate papers used this concept to 1) examine the intrapersonal-level determinants of the full spectrum of PA 2) examine how the total number of life events and the self-reported stress of life events influences the full spectrum of PA; and 3) examine the longitudinal relationship of the full spectrum of PA with adiposity and weight. This dissertation used objectively measured physical activity data collected as part of The Energy Balance Study to examine the three specific aims. The purpose of the Energy Balance Study was to examine the extent to which variation in total energy expenditure (TEE) and variation in total energy intake (TEI) contribute to changes in body weight and fat among adults. A secondary aim was to examine specific components of TEE and TEI that drive changes in body weight and fat. This dissertation contributes answers to this secondary aim, by examining the physical activity component of TEE.

Study 1 showed that intrapersonal variables within categories of biological, socioeconomic, family structure, behavioral, and psychological can influence activity. The associated characteristics differ based on whether physical activity is quantified as MVPA-10, total MVPA, or total PA. Adding components of baseline PA, first short bouts of total MVPA followed by light intensity PA influences the results.

In the second study, the average number and associated stress of life events per quarter did not have much influence on physical activity. However, many life events when examined separately had significant associations with MVPA-10, total MVPA and total PA. For young adult men, changing jobs and marriage had negative impacts on activity while starting/ending a relationship and beginning a mortgage had positive influences. For young adult women, starting a new job, moving, engagement, and the loss of a family/friend had negative consequence while quitting a job resulted in increases in PA. The degree of influence on activity often went beyond the typical recommendations of MVPA in 10 minute bouts.

In the third study, physical activity had an influence on various anthropometric measures and varied by gender. The accumulation of greater amounts of activity was associated with a lower body fat percentage for both men and women. There were also associations with PA for waist circumference, hip circumference, and BMI for the women. For all anthropometric associations there were similar degrees of association for MVPA-10 and total MVPA, suggesting that the accumulation of all MVPA regardless of bout length can have a similar influence on anthropometrics. The association of anthropometrics with total PA was typically half of the impact when comparing the MVPA categories. Thus an increase of MVPA has a greater influence on anthropometric outcomes than an increase in total PA.

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