The effects of intensive aerobic exercise, weight control, and no treatment on (1) stress reactivity (measured by weight loss, glucocorticoid elevation, and incidence of gastric lesions) and (2) myocardial morphology were compared in male Sprague-Dawley ulcer susceptible rats. Animals were allocated to a free-feeding exercise group aerobically conditioned by a 26 week treadmill-running program; a sedentary group whose mean body weight was made to parallel that of the exercise group; and a free-feeding sedentary group. In week 27 animals were stressed for five days with daily presentation of escape trials on a variable interval schedule. Differences were found between the heart tissues of the exercised and the sedentary animals: both sedentary groups evidenced adverse morphological changes in ventricular tissue and microcirculation, while the myocardia of the exercise group were completely free of such changes. In response to the stress procedure significant differentiation between groups was obtained only on the weight index. After an initial loss, the exercise group commenced to gain weight on the fourth stress day, while the control groups continued to lose weight. © 1978.
Birrell, P., & Roscoe, C. (1978). Effects of intensive aerobic exercise on stress reactivity and myocardial morphology in rats. Physiology and Behavior, 20(6), 687–692. https://doi.org/10.1016/0031-9384(78)90293-7