Browsing by Subject "Physical activity"

Physical activity has many benefits including promoting healthy aging, reducing risk of chronic disease, and supporting general well-being. Despite this, many adults do not get significant amounts of daily physical activity. The effects of interventions promoting physical activity are highly variable and typically modest. Even when behavioral interventions are effective, the understanding of how and why they work is lacking. Understanding the determinants of physical activity behavior change, along with identifying evidence-based behavior change techniques that target these determinants, is critical for developing effective interventions. In this dissertation, across two studies, I examine the role of neural and behavioral determinants of physical activity behavior change. Chapter 1 provides a review of the two prominent theoretical approaches to physical activity behavior change, social cognitive theory and dual-process theory, and highlights how neuroimaging techniques can be utilized to help inform gaps in both theoretical and applied knowledge of physical activity. Chapter 2 (Study 1) evaluates if there are brain regions correlated with physical activity behavior change. In the study, participants wore a pedometer for a week before and after an fMRI session where they read and heard statements about walking. Behavioral analysis demonstrated that participants walked significantly more following exposure to the walking-related messages. Whole-brain analysis examined regions positively associated with walking behavior change and produced two significant clusters in the frontal pole region and the precuneus/posterior cingulate gyrus region. The frontopolar cortex is implicated in pre-commitment, a self-control strategy where people anticipate self-control failures and prospectively restrict their access to tempting alternatives. The precuneus/posterior cingulate cortex region has been found to play a role in self-relevant processing. Both self-control and self-relevant processing are believed to be important for behavior change. Chapter 3 (Study 2) focuses on neural and self-report responses to different types of health messages and their ability to predict physical activity behavior change. In the study, participants completed an fMRI task where they read positively or negatively framed walking-related messages with either social or non-social based content and rated how personally motivating they were as well as other self-reported ratings. Neural activity in regions involved in positive valuation and self-referential processing were measured to evaluate whether sensitivity in these regions to individual messages could predict the effectiveness of those messages when delivered in an intervention weeks or months later. For the next 80 days, participants completed a SMS-based mHealth intervention where they received one of the same walking-related messages from the scanner task daily. We assessed physical activity using a wearable fitness tracker throughout the 80 days and a baseline period. Individual participant ratings on how relevant the message would be to others predicted the effectiveness of the messages. People were more physically active on days when they received messages that were rated as more relevant to others. Brain activation in the regions of interest selected were not associated with message effectiveness during the intervention.

The current study examined the relationships among the neighborhood environment, levels of self-efficacy, health behaviors, and health outcomes among adults in the United States. The goals of the research were as follows: 1. To examine the role that health behaviors play in the relationship between neighborhood and health; 2. To determine whether health-related self-efficacy mediates or moderates the relationship between neighborhood and health behaviors; 3. To investigate potential gender, education, and race differences in the relationships among the constructs.

The study included 5,600 whites and 321 blacks who participated in the first wave of the National Survey of Midlife Development in the Unites States (MIDUS I). The age range of the sample was 20-75 (mean= 47.14 years) and roughly half of the participants were male (47.4%). Data on the neighborhood (including safety, physical conditions, social cohesion, and homeplace), health-related self-efficacy, health behaviors, and the health outcomes of self-rated health, obesity, and cardiovascular disease were collected through telephone interviews and self-report questionnaires.

Structural equation modeling was employed to address the research goals. The results showed that self-efficacy mediated the relationship between neighborhood and physical activity and that health behaviors mediated the path between neighborhood and physical activity. However, self-efficacy did not serve as a moderator in the association between neighborhood and physical activity. Demographic differences were found according to age, gender, race, and education. Specifically, the model was particularly salient for late midlife and older adults, females, and those with some college education. Furthermore, the impact of neighborhood factors on self-efficacy was greater for blacks than whites.

The present findings contribute to the literature by elucidating the interrelations among neighborhood and the individual-level factors of self-efficacy and physical activity in predicting health outcomes. Furthermore, the direct effect of physical activity on health outcomes suggests that physical activity engagement should be a particular area of intervention focus, especially among older adults and women. Future research should include objective measures of neighborhood, physical activity, and health, additional contexts such as the workplace, individuals above the age of 75, and greater representation of minority groups.

Over the past decade, exercise has gained increasing attention from both clinicians and patients as a beneficial adjunct therapy to maintain or enhance quality of life in breast cancer patients. Recent epidemiological studies indicate that aerobic exercise following a diagnosis of breast cancer may be associated with reductions in cancer-specific and all-cause mortality. However, the mechanisms by which physical activity affects tumor physiology are poorly understood. Accordingly, clinicians lack critical information to properly advise breast cancer patients on the use of exercise as an adjunct to more conventional therapies.

The beneficial effects of exercise on systemic vasculature are well known, including improved endothelial function and increased perfusion. In this work, we evaluate the hypothesis that exercise slows tumor growth and improves the structure and function of tumor blood vessels, resulting in decreased hypoxia and increased effectiveness of cyclophosphamide chemotherapy

To investigate the effects of exercise on tumor microenvironment, we injected syngeneic 4T1 breast tumor cells into the mammary fat pad of immunocompetent BALB/c mice. The exercise intervention (voluntary wheel running) was designed to mimic four clinically relevant scenarios: 1- patients who are sedentary before and after diagnosis, 2- previously sedentary patients who begin exercising after diagnosis, 3- previously active patients who stop exercising after diagnosis, and 4- previously active patients who continue to exercise after diagnosis. Animals in Groups 3 and 4 exercised prior to tumor cell transplant, whereas Groups 1 and 2 were sedentary during that time. Immediately after transplant, Groups 2 and 4 were running, and Groups 1 and 3 were sedentary. Tumor growth was monitored for 18 days, and then perfusion was mapped using MRI and tumors were removed for analysis. In a follow-up experiment, BALB/c mice were immediately implanted with tumor cells and then randomized to running or sedentary conditions with or without cyclophosphamide chemotherapy given one week after tumor transplant (three 100 mg/kg doses, every other day). Tumors were again allowed to progress for three weeks, and MRI was performed prior to tumor removal.

Animals voluntarily ran 5-6 km per day prior to transplant and 4-5 km per day after transplant. Body weight was unaffected by exercise. Voluntary wheel running reduced tumor growth rate nearly twofold and significantly increased apoptosis. Additionally, running after tumor implantation caused significant increases in microvessel density (CD31) and vessel maturity (colocalization of CD31 with NG2 and desmin). Hypoxia (EF5) was significantly reduced in the exercising animals, and MRI showed that tumors were more uniformly perfused in the running groups. Furthermore, exercise significantly enhanced the effectiveness of cyclophosphamide in slowing tumor growth. Taken together, these results suggest that aerobic exercise slows breast tumor growth, improves tumor vessel structure and function, and augments the effectiveness of cyclophosphamide chemotherapy.

These findings have important implications for the use of exercise in cancer treatment. Using a clinically relevant animal model, we provide the first conclusive evidence that exercise may do more than decrease symptoms and improve quality of life for cancer patients. Our data suggest that exercise may, in fact, be an effective anti-tumor intervention both alone and in combination with other cytotoxic therapies.

Background

Methods

Discussion

Trial registration