Within-person relationships among pain intensity, mood and physical activity in chronic pain: a naturalistic approach.

Fifty-seven chronic pain patients rated their pain intensity, mood and activity level, at a random time schedule, eight times a day during 6 consecutive days, according to the Experience Sampling Method (ESM). Within-person correlations among pain intensity, mood and activity level were calculated. We found pain intensity to be significantly associated with mood. However, the associations between pain intensity and activity level, and activity level and mood could not be supported. Further, we examined whether the relationship between pain intensity and mood was the result of a pattern across the day. Results showed that pain intensity and mood were worst in the morning and improved during the afternoon among participants whose pain intensity and mood were correlated significantly. We suggest that attentional as well as behavioural processes might explain the established day pattern of pain intensity and mood.