Exercise-induced modulation of pain sensitivity in healthy women

Exercise influences pain sensitivity. Research shows that sensitivity to pain decreases during and following exercise (exercise-induced hypoalgesia, EIH) and that being physically active is associated with being less sensitive to pain. However, exercise itself is often painful. This contradiction forms the basis for three studies which were designed to determine how acute exercise and physical activity and sedentary behaviors influence pain processing and perception in women. Study 1: Primary Aim - To test whether conditioned pain modulation (CPM) is a mechanism of EIH. Sixteen women completed pain testing during three separate sessions: 10 minutes of painful cycling exercise, 10 minutes of non-painful exercise and 10 minutes of quiet rest. Results demonstrate that naturally occurring muscle pain induced by exercise may contribute to EIH through CPM. Study 2: Primary Aim - To determine whether having a physically active lifestyle is associated with reductions in sensitivity to pain. Relationships between pain sensitivity and physical activity and sedentary behaviors were assessed in 21 women. Results showed that women with an active lifestyle consistent with current physical activity recommendations were less sensitive to pain than their less active peers and that vigorous physical activity was important for this benefit. Study 3: Primary Aims - To assess brain responses associated with EIH, the effects of physical activity and sedentary behaviors on brain and behavioral responses to pain, and the effects of acute exercise on the fMR1 BOLD response. Twelve women were exposed to pain stimuli during two functional neuroimaging scans: one post-exercise and one following quiet rest. Results showed that physical activity and sedentary time predicted brain and behavioral responses to pain and that acute exercise influenced these relationships but did not result in EIH. The cardiopulmonary response to exercise resulted in greater variability in the BOLD signal compared to quiet rest. Our results suggest that naturally occurring muscle pain may serve as a mechanism of EIH through CPM and that physical activity is beneficial for pain sensitivity while sedentary time may be detrimental. Further, acute exercise influences the BOLD response and cardiopulmonary responses to exercise should be accounted for in functional neuroimaging research.