Autonomic nervous system adaptations to short-term exercise training

Signs of sympathetic hyperactivity and low parasympathetic activity have been found during the acute and recovery phases of myocardial infarction and have been associated with an increased risk of cardiac mortality. Beneficial effects of physical training have been recently reported in postmyocardial infarction patients. We tested the hypothesis that physical training would be effective in improving the autonomic balance by studying 22 patients with a first and recent myocardial infarction who were randomly assigned to enter or not enter a 4-week in-hospital physical training program. Spectral indices of heart rate variability were analyzed at rest and during 70° head-up tilt before and after the index training, not training period. As expected, physical training induced a significant increase in exercise duration (13.7±0.8 vs 17.1±0.1 min, p