PROJECT SUMMARY/ABSTRACT Health disparities for Latinas remain a persistent problem leading to increased incidence of chronic disease, comorbidities and premature mortality. The NIH has called for interventions that improve adherence to prevention regimens (NOT-OD-21-100) because of the potential to decrease health disparities by reducing disparities in meeting health guidelines. There has been little research into interventions to improve meeting and adhering to behavioral health guidelines, especially in understudied Latinas. Often the process of adopting new health habits is challenging for marginalized communities who have fewer resources and time to invest in healthy behaviors. In particular, stress can be a barrier to adopting new habits. This study aims to address the everyday stress faced in the general population of Latina women in their daily lives that can be interfering with their ability to adhere to prevention regimens such as meeting physical activity (PA) guidelines. Our research team has significantly improved total PA minutes and the number of Latinas meeting PA guidelines through rigorous research and theory-based interventions, delivered remotely with technology. Nonetheless, only 40% of women meet PA guidelines at 6 months. We have shown that participants who experience the stress relieving benefits of PA, regardless of baseline stress levels, are more likely to meet and adhere to PA guidelines and that Mindfulness-Based Stress Reduction (MBSR) can increase PA minutes, improve other health behaviors, as well as reduce stress. It is our goal to optimize our PA intervention by integrating the most potent ingredients from MBSR for those women who do not meet PA guidelines at 6 months. With an innovative SMART design, all participants, inactive Latinas aged 18-65 (n=258), will receive our evidence based PA intervention. At 6 months, participants will be objectively assessed for meeting PA guidelines. Women who meet the guidelines will continue to receive the standard intermittent PA for another 6 months. Women who do not meet the PA guidelines (»60%), will be randomized to continue intensive PA counseling or attention matched PA counseling incorporating the most potent components from MBSR adapted for PA. Participants in all arms will be followed and compared over 18 months. We will also rigorously evaluate stress as a mechanism for meeting PA guidelines using multiple measures to better assess the causal relationship including cortisol, self report, and daily Ecological Momentary Assessment and stress context. Finally, we will strengthen evidence for the longer term heart health benefits of meeting PA guidelines and reducing stress, by using laboratory based assessments of weight, blood pressure, HbA1c, and lipid profiles. This study has the potential to advance intervention science by optimizing an evidence based intervention to deliver greater improvements in health behaviors and health outcomes.