Rates of obesity and related medical conditions (e.g., diabetes) are high in the Latino population, particularly among Latinas [1
]. Lifestyle factors, such as inactivity, contribute to this public health crisis. Sedentary behaviors (i.e., television viewing) are often an integral part of family life in this community. For example, in past studies, Latina focus group participants reported frequently watching telenovelas in the evening with family, watching TV during meals, and using TV as babysitter and tool to learn English [2
]. On the other hand, finances, gender roles, and caretaking responsibilities can be major barriers to Latinas engaging in the recommended levels of physical activity (150 minutes of weekly moderate or vigorous physical activity). According to recent CDC data [4
], 53.4% of Latinos reported engaging in no leisure time activity, compared to 35.3% non-Hispanic Whites. Effective interventions are obviously needed, yet the high (and rising) rates of obesity in this group highlight the need to determine if existing physical activity interventions are equally effective across the body mass index (BMI) range.
While previous research has shown that higher BMI is associated with less physical activity [5
], there is limited evidence regarding the relationship between baseline BMI on subsequent change in a physical activity intervention. King and colleagues found that individuals with BMI > 31
were engaging in, on average, far less than the recommended activity levels at every measurement point over a 2-year intervention. In contrast, participants with BMI < 31
were, on average, exceeding the guidelines. While this study was conducted with predominantly White, non-Hispanic men and women, such findings emphasize the need to understand the role of BMI on adoption of physical activity and raises questions about whether general physical activity interventions will meet the needs of obese participants as well as nonobese participants. As prevalence rates of obesity among Latinas are much higher than non-Hispanic Whites, investigation into how BMI might specifically affect the success of Latinas in a physical activity intervention is needed and will help inform future efforts to better serve this population.
The Transtheoretical Model (TTM) [7
] and the Social Cognitive Theory (SCT) [8
] are two theoretical models frequently used in physical activity promotion. TTM states that individuals move through a series of stages (i.e., Precontemplation, Contemplation, Preparation, Action, and Maintenance) when starting and maintaining physical activity. As individuals move through the stages, TTM states that people weigh the pros and cons of becoming active. In addition, individuals use behavioral and cognitive processes or strategies to help them move through the stages. Behavioral processes refer to engaging in activities such as enlisting social support, rewarding yourself, and reminding yourself. Cognitive processes refer to activities such as increasing knowledge, comprehending benefits, and increasing healthy opportunities. Similarly the SCT states that there are behavioral and cognitive factors that influence individual's behaviors, such as social support and self-efficacy. Self-efficacy is one of the most central factors to behavior change for the SCT and refers to an individual's confidence about being physically active. Using a theoretical framework, such as SCT, is important for being able to properly implement and test an intervention. A review of physical activity interventions with Latinas found that only 6 out of the 12 interventions used any theoretical model, and the model that was most commonly used was the Social Cognitive Theory (Sharma, 2008 obesity reviews). Four out of those 6 studies used the SCT and all 4 studies that used SCT were successful in increasing physical activity, further supporting the need for theory-based interventions.
Thus, using data from the intervention arm of a trial of a six-month, culturally and linguistically adapted intervention for Latinas (N
= 45) [9
], that was developed and individually tailored based on TTM and SCT, the current study assessed whether baseline BMI predicted changes in minutes of at least moderate intensity physical activity and changes in associated SCT and TTM theoretical constructs (self-efficacy, cognitive and behavioral processes, and social support) targeted by the intervention over time. The two aims of the study were (1) to assess how BMI impacts Latinas' success in increasing physical activity and (2) to assess how BMI impacts success in changing theoretical constructs targeted by the intervention. We hypothesized that participants with lower BMIs would report greater increases in physical activity and greater changes to the theoretical constructs self-efficacy, cognitive and behavioral processes, and social support, in response to a theory-based physical activity intervention than women with higher BMIs.