PROJECT SUMMARY Approximately 42% of new cancer cases in the U.S. are viewed as potentially avoidable, including 15% caused by excess body weight and physical inactivity. However, most U.S. adults are physically inactive. Physical activity intervention research has focused primarily on modifying cognitions about what a rationally-thinking person “should” do to improve their health, resulting in modest effects on long-term behavior change. A factor that has been largely overlooked in intervention research is that while engaging in physical activity may be pleasant for some, it can be an extremely unpleasant experience for others. How someone feels during behavior can trigger associative processes including implicit attitudes (e.g., favorable/unfavorable) towards the target behavior that operate quickly and involuntarily outside of cognitive control. A recent meta-analysis showed a significant positive association between positive implicit attitudes towards physical activity and physical activity engagement. Our data show implicit attitudes towards physical activity differ from day to day and across situations. A variety of experimental strategies such as guided imagery and visualization have shown promise in changing implicit attitudes towards physical activity. However, rarely have these intervention strategies been delivered in real- world settings on a regular basis to address variations in implicit attitudes. We will examine whether implicit attitudes towards physical activity can be experimentally manipulated by “affect-based” intervention strategies delivered daily through interactive mobile technology and mediate intervention effects on physical activity behavior. The proposed study will add innovative real-time measures of implicit attitudes during daily life among adults (18+ years) at elevated cancer risk due to inactivity and overweight/obesity participating in an ongoing trial (N=120). An “affect” condition provides daily goals related to enjoyment and feeling good during physical activity. In contrast, an “intensity” comparison condition provides daily heart rate goals. Two daily enhancements to the affect-based condition are evaluated: (1) tailored activity type and context recommendations to satisfy personally important psychological needs (TYPE/CONTEXT) and (2) savoring practices to increase the saliency of positive emotions during physical activity (SAVOR). On each day that they plan to engage in physical activity, implicit attitudes will be assessed by a morning mobile Implicit Associations Test (IAT) on their smartphone capturing reaction times to categorize physical activity and sedentary words as good or bad. Physical activity outcomes are measured using accelerometry. Specific aims are (1) determine whether implicit attitudes mediate effects of treatments on physical activity and (2) explore cross-situation moderating effects such as situational constraints (e.g., incidental stress, pain, fatigue). This study will elucidate h...