Mean ACTH concentrations (+/− SEM) of the exercise, increased cage complexity, or control groups over the successive days (1, 4, 8, and 11) of repeated loud noise (98-dBA) stress. On day one, exercise animals had a reliably reduced ACTH response compared to increased cage complexity and control animals. Responses were statistically equivalent on each of the remaining sampling days. #: Exercise group significantly different from both control and increased cage complexity groups, Tukey's HSD (p'< 0.05).