Objective: To understand the predictors and consequences of adolescent moderate-to-vigorous physical activity (MVPA) and sedentary behavior in nearly real-time.Methods: Participants were 26 adolescents ( M age = 15.96, SD = 1.56) who provided 80 self-reports of subjective states and continuous objective reports of MVPA and sedentary behavior over 20 days.Results: Random effects were observed for all of the models with affect and feeling variables predicting MVPA. There was a negative fixed effect for within-person positive affect and sedentary behavior and the inverse association for negative affect. Within-person MVPA was a significant positive predictor of positive affect and energy. There was a random effect for within-person MVPA and fatigue. There was a significant random effect for within-person sedentary behavior predicting positive affect. Within-person sedentary behavior was a significant negative predictor of energy.Conclusions: Findings highlight the importance of the intrapersonal nature of the associations among subjective states and physical activity.