Older adults (55+ yrs) represent a rapidly growing population and are at an increased risk of developing age-related, non-communicable diseases. Despite the health benefits of aerobic exercise, poor adherence remains a concern. As feelings of pleasure/displeasure (affective valence) during exercise predict future intentions/behavior, researchers have explored determinants of affective valence during aerobic exercise, but no studies used a sample of older adults. PURPOSE: To understand the determinants of recalled in-task affective valence experienced during a regularly performed aerobic bout in older adult exercisers. METHODS: Participants were regular exercisers (≥90 min/week, ≥ 3 mo.). Qualitative data were collected using 1-on-1 interviews conducted virtually, and heart rate (HR) was collected using a smartphone application. Interviews were structured so that individuals recalled deviations (feeling more pleasant or more unpleasant than normal) in affective valence in response to a regularly completed aerobic bout. Thematic analyses were conducted to construct themes and sub-themes. RESULTS: Sixteen older adults (69% women, 61±5yrs, HR 66±10 bpm) provided data. Two themes emerged regarding determinants of recalled in-task affective valence. Theme one, ‘Person-Specific Conditions,’ was composed of two sub-themes: perceived performance, and physiological and psychological readiness to exercise. Theme two, ‘External Conditions,’ was composed of two sub-themes: environmental context of exercise and social context of exercise. When recalling a more pleasant session, 44% of participants indicated an associated increase in volume and/or intensity. When recalling a more unpleasant session, 75% indicated an associated decrease in volume/intensity. CONCLUSIONS: When recalling differing affective responses to a regularly performed aerobic bout, the older adults in this sample indicated that such responses were determined by factors cited previously (pre-exercise states, performance), as well as novel factors (physical and social environment) that may pertain to performing exercise in the free-living environment versus a controlled laboratory setting. Further, volitional modifications to planned exercise volume appear more responsive to feelings of displeasure.