abstract: This study utilized targeted messages and expert and referent sources in an effort to promote physical activity behavior in college students. College students aged 18-25, excluding collegiate athletes, were randomized into three conditions using their current physical activity level. Two of the conditions received targeted messages highlighting three primary components of social cognitive theory - self-efficacy, outcome expectations, and goals - while the third condition received no messages. In addition, the experimental conditions received the messages from either an expert (i.e., a personal trainer) or a referent (i.e., a close friend). In this way, this experiment analyzed whether receiving social cognitive theory messages increased physical activity indicators compared to the control condition, as well as if the message source caused differences in the physical activity indicators. Moreover, participants completed Time 1 and Time 2 measures to determine if receiving messages or not caused changes over a one week time period. Seven physical activity indicators were assessed: self-efficacy, positive outcome expectations, negative outcome expectations, attitudes, response-efficacy, intentions, and physical activity behavior. Results revealed that both the personal trainer and close friend conditions had significantly higher scores than the control condition for intentions at Time 1 and Time 2, as well as physical activity behavior at Time 2. Moreover, the personal trainer condition had significantly higher positive outcome expectations compared to both the friend and control conditions. No other significant differences were found across conditions for Time 1 attitudes, response-efficacy, negative outcome expectations, self-efficacy, and Time 2 attitudes, and self-efficacy. Overall, targeted messages were effective in increasing physical activity intentions and behavior regardless of the message source. / Dissertation/Thesis / Ph.D. Communication 2012