Treadmill running produces both positive and negative physiological adaptations in Sprague-Dawley rats

Exercise training produces a vast array of physiological adaptations, rangi ng from changes in metabolism to muscle mitochondrial biogenesis. Researche rs studying the physiological effects of exercise often use animal models t hat employ forced exercise regimens that include aversive motivation, which could activate the stress response. This study examined the effect of forc ed treadmill running (8 wk) on several physiological systems that are sensi tive to training and stress. Forced treadmill running produced both positiv e and negative physiological adaptations. Indicative of positive training a daptations, exercised male Sprague-Dawley rats had a decrease in body weigh t gain and an increase in muscle citrate synthase activity compared with se dentary controls. In contrast, treadmill running also resulted in the poten tially negative adaptations of adrenal hypertrophy, thymic involution, decr eased serum corticosteroid binding globulin, elevated lymphocyte nitrite co ncentrations, suppressed lymphocyte proliferation, and suppressed antigen-s pecific IgM. Such alterations in neuroendocrine tissues and immune response s are commonly associated with chronic stress. Thus treadmill running produ ces both positive training adaptations and potentially negative adaptations that are indicative of chronic stress. Researchers employing forced activi ty need to be aware that this type of exercise procedure also produces phys iological adaptations indicative of chronic stress and that these changes c ould potentially impact other measures of interest.