Prior Aerobic Exercise Training Fails to Confer Cardioprotection Under Varying Exercise Volumes in Early...

Background: There is no information on how the dose of exercise training prior to myocardial infarction (MI) affects cardioprotection. Objective: This study aimed to evaluate the cardioprotective role of different volumes of exercise training prior to MI. Methods: Wistar female rats were allocated to one of the following groups: SHAM (not trained and undergoing simulated MI surgery), NT+MI (untrained and undergoing MI surgery), T60+MI (trained 60 min per session and undergoing MI surgery), T90+MI (trained 90 min per session and undergoing MI surgery), and T180+MI (trained 180 min per session and undergoing MI surgery). The training protocol was performed in a swimming pool for eight weeks. On the seventh day after MI, the animals underwent left ventricular (LV) structural and functional evaluation and were euthanized for molecular analyses. Results: Exercise training groups had greater VO₂peak and LV mass than did the SHAM group. The MI size did not differ statistically among the experimental groups. Compared with the SHAM group, all the MI groups presented a lower LV shortening fraction. LV systolic pressure was significantly lower in the T60+MI group than in the SHAM and T180+MI groups. The +dP/dt of the LV was significantly lower in the NT+MI, T60+MI, and T90+MI groups than in the SHAM group. We did not find significant changes in the inflammatory mediators and oxidative stress markers as well as proteins involved in calcium handling. Conclusions: Exercise training prior to MI enhanced cardiorespiratory fitness and induced LV hypertrophy, however, regardless of volume, was unable to counteract the detrimental effects of MI.