Influence of moderate and high intensity interval training on infarcted rat diaphragm

Abstract

Background Respiratory muscle dysfunction is commonly observed in heart failure (HF) patients and contributes to early fatigue and dyspnea. As there is no specific pharmacological therapy to treat skeletal muscle changes, physical exercise is considered an important strategy to prevent HF-associated skeletal myopathy. However, which exercise type is better during HF is unsettled. Purpose To evaluate the effects of aerobic and high intensity interval (HIIT) training on diaphragm morphometric, biochemical, and molecular parameters in infarcted rats. Methods Three months after inducing myocardial infarction (MI), male Wistar rats were assigned into three groups: sedentary MI (MI-Sed, n=8), MI subjected to aerobic exercise (MI-A, n=8), and MI subjected to HIIT (MI-HIIT, n=8). Results were compared to a Sham group (n=8). Exercise was performed in treadmill three times a week for three months. Functional capacity test and echocardiogram were performed before and after exercise protocols. Myosin heavy chain (MyHC) isoforms were analyzed by electrophoresis; diaphragm mitogen activated protein kinases (MAPK), NF-κB, TNF-α, and Pax-7 protein expression was evaluated by Western-blot. Statistical analysis: ANOVA. Results Functional capacity was similarly improved by both exercise protocols. Infarction size evaluated by histological analysis did not differ between groups (MI-Sed 27.7±10.8; MI-A 29.6±12.9; MI-HIIT 27.4±12.2% of total left ventricle area; p=0.91). Echocardiographic parameters did not differ between MI groups before and after exercise. Cross sectional area of diaphragm fibers (Sham 1922±230; MI-Sed 1808±264; MI-A 1926±209; MI-HIIT 2007±286 μm2), collagen interstitial fractional area (Sham 4.93±1.76; MI-Sed 5.01±1.88; MI-A 4.55±1.18; MI-HIIT 3.94±1.15%), and percentage of MyHC isoforms did not differ between groups. Pax-7 expression was lower in MI-HIIT than MI-Sed and MI-A [Sham 1.15 (0.58–1.44), MI-Sed 1.19 (0.90–2.85), MI-A 1.46 (0.77–2.14), MI-HIIT 0.46 (0.29–0.66) arbitrary units]. Total p-38 expression was higher in MI-Sed than the other groups and lower in MI-HIIT than Sham [Sham 1.00±0.52; MI-Sed 1.77±0.47; MI-A 0.66±0.22; MI-HIIT 0.46±0.31 arbitrary units]. The other proteins did not differ between groups. Conclusion Both aerobic and high intensity interval training improves functional capacity with no influence on diaphragm of rats with myocardial infarction. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): FAPESP (São Paulo Research Foundation)