Adaptations of the hypothalamic pituitary adrenal (HPA) axis to voluntary exercise in rodents are not clear, as most investigations use forced exercise protocols, which are associated with psychological stress. In the present study, we examined the effects of voluntary wheel running on the circadian corticosterone (CORT) rhythm as well as HPA axis responsiveness to, and recovery from restraint stress. Male, Sprague-Dawley rats were divided into exercise (E) and sedentary (S) groups, with E rats having 24h access to running wheels for 5 weeks. Circadian plasma CORT levels were measured at the end of each week, except for week 5 where rats were exposed to 20 minutes of restraint stress, followed by 95 minutes of recovery. Measurements of glucocorticoid receptor (GR) content in the hippocampus and anterior pituitary were performed using western blotting at the termination of the restraint protocol. In week 1, circadian CORT levels were 2-fold higher in E compared to S animals, but progressively decreased in the E group throughout the training protocol to reach similar values observed in S by week 4. During restraint stress and recovery, CORT values were similar between E and S, as was GR content in the hippocampus and pituitary gland following sacrifice. Compared with E, S animals had higher plasma ACTH levels during restraint. Taken together, these data indicate that 5 weeks of wheel running are associated with normal circadian CORT activity, and normal negative feedback inhibition of the HPA axis, as well as, increased adrenal sensitivity to ACTH following restraint stress.