High-Intensity Interval Training Improves Functional Capacity and Peripheral Skeletal Muscle Energy Metabolism in Infarcted Rats

Introduction: High-intensity interval training (HIIT) has been recommended in post-myocardial infarction (MI) cardiac rehabilitation; however, its effects on MI-induced cardiac remodeling and skeletal muscle remain unclear. This study evaluated the effects of HIIT on functional capacity, cardiac remodeling, and the soleus skeletal muscle in rats after long-term MI. Methods: Three months after MI induction, Wistar rats were assigned to Sham, MI, and MI subjected to HIIT (MI-HIIT) groups. HIIT was performed three times per week for three months on a treadmill. Cardiac function and functional capacity were assessed before and after training. Oxidative stress markers, energy metabolism enzyme activities, and trophism were analyzed in the soleus. The statistical analysis included ANOVA and Bonferroni or Kruskal–Wallis and Dunn tests. Results: HIIT improved functional capacity compared to the Sham and MI groups. The infarcted groups had left ventricular dilation, hypertrophy, and systolic dysfunction, which were not modulated by HIIT. Soleus fiber cross-sectional areas did not differ between the groups. Catalase activity was lower in the MI and MI-HIIT groups than in the Sham group, while other oxidative stress markers were unchanged. HIIT increased citrate synthase activity compared to the Sham and MI groups, and phosphofructokinase and carnitine palmitoyltransferase-1 activities compared to the MI group. Conclusions: High-intensity interval training improves functional capacity despite unchanged cardiac remodeling in long-term infarcted rats. Enhanced physical capacity is associated with the increased activity of the enzymes involved in the energy metabolism of the soleus muscle.