# Moderate-Intensity Swimming Alleviates Oxidative Injury in Ischemic Heart
## 4 Discussion  
Our experimental study was aimed at examining the impact of pre-emptive moderate physical exercise, in the form of swimming, on cardiac parameters after myocardial infarction from the perspective of changes in antioxidant capacity and oxidative stress. The positive effects of physical exercise as a preconditioning method in myocardial ischemia and reperfusion injury models are well documented. Running in particular had been shown to improve post-ischemic cardiac output [13], and in one of our previous studies, we found that it also helps in reducing oxidative stress, through increased cardiac heme oxygenase and GSH activity as well as reduced myeloperoxidase activity [12]. Moreover, according to [PERSON] et al. [14], swimming before the onset of ischemia helps regulate heart rate and contractility after reperfusion. In addition, short-duration swimming as a part of a post-infarction treatment reduces mortality, improves left ventricular ejection fraction and fractional shortening, reduces interstitial fibrosis and myocardial apoptosis, improves mitochondrial size homogeneity, reduces ROS content, and inhibits SOD acetylation, thus increasing its enzymatic activity [15]. In our current study, we managed to provide further evidence that preconditioning via moderate-intensity swimming is an efficient method to reduce the severity of cardiac injury caused by myocardial ischemia, through the stimulation of the antioxidant system and the reduction in overall ROS production. For the assessment of cardiac damage after ISO treatment, we decided to use serum atrial and brain natriuretic peptide concentrations as indicators for ischemic injury. Elevated BNP and N-terminal prohormone of BNP (NT-proBNP) levels in particular have long been considered, alongside cardiac troponin, to be one of the most reliable biomarkers  
Figure 5: The effects of swimming training on cardiac ROS concentration (ROS; expressed as U/mg protein). Results shown as means \(\pm\) S.E.M. \(n\) = 5–6. *: \(p\) < 0.05 statistical comparison between ISO and Pre + ISO groups. #: \(p\) < 0.05 statistical comparison between ISO and CTRL groups. Pre + ISO = pre-swimming training + ISO treated; ISO = isoproterenol-treated; CTRL = control; and ROS = reactive oxygen species. in the clinical diagnostic process for heart failure associated with systolic and diastolic dysfunction, left ventricular hypertrophy, valvular heart disease, and ischemia [7]. Furthermore, animal studies focused on post-myocardial infarction also frequently use elevated serum BNP concentration as evidence for the presence of cardiac damage [16]. Similarly, ANP, which is synthesized, stored, and secreted by atrial cardiac cells, is also considered an important factor in establishing the severity of cardiac dysfunctions and heart injuries. Myocardial wall stretching in the atrium, a common pathological feature of acute and chronic congestive heart failure, induces the secretion of pro-ANP, which is converted into biologically active \(\alpha\)-ANP by the serine protease corin, thus rapidly increasing the serum ANP concentration [17]. In animal studies conducted on rats with myocardial infarction-induced heart failure, both ANP and BNP expressions were repeatedly shown to be significantly increased [18; 19]. Our results regarding the connection between ANP and BNP levels and myocardial infarction are in line with the consensus found in the associated literature. We found that both ANP and BNP serum levels were significantly increased after ISO treatment, suggesting post-ischemic cardiac damage; however, in rats preconditioned with moderate-intensity swimming training, these increases in the concentrations of cardiac injury biomarkers are not present. Regarding the oxidative stress theory, the idea that oxidative damage and the alteration in the intracellular antioxidant system have a significant role in the development of pathologic changes followed by myocardial infarction and subsequent ischemia is a well-accepted one.