Pathological exercise (PE) is a common feature of individuals with eating disorders (ED) and
represents a key maintaining factor of eating pathology. However, little is known about
underlying mechanisms that maintain PE and whether these mechanisms are influenced by the
occurrence of PE in the context of an ED. The present study tested hypotheses that women with
PE would 1) experience exercise as more reinforcing, 2) show greater cortisol reactivity in
response to exercise, and 3) that greater cortisol reactivity in response to exercise would predict
greater increases in positive affect following exercise. Participants (N=64 women total, n=16 PE
with ED, n=16 PE Only, n=16 ED Only, n=16 Control) completed a computerized progressive
ratio (PR) task to earn running time on a treadmill as a measure of the reinforcing value of
exercise. HPA-axis response to acute exercise was measured through salivary cortisol and
changes in affect were measured by a self-report questionnaire. Participants provided four saliva
samples and self-report ratings directly prior to and 0-, 20-, and 40- minutes after running for 30
minutes on a treadmill at 75% maximum heart rate. Results indicated that women with PE had
significantly higher reinforcing value of exercise (p<.001) and showed higher cortisol reactivity
to exercise (p<.001). Contrary to hypotheses, cortisol reactivity to acute exercise did not predict
exercise-induced changes in affect in the full sample. Cortisol reactivity significantly predicted
breakpoint on the PR task (p<.001) in the full sample. Overall, findings provide preliminary
evidence that women with PE may experience exercise as more rewarding than normal
exercisers, which may be attributable to dysregulations in underlying biological mechanisms that
influence its reinforcing value. Given limitations of the current study, future studies should use
ecological momentary assessment to better understand factors driving associations between PE,
reward, and dysregulations in HPA-axis activity in participants' natural environment.