Endurance Training in Young Subjects: Effects on the Autonomic Nervous System

We examined the effects of exercise on the autonomic nervous system and blood parameters in young men and women before and after training. Ten healthy young subjects (5 men, age 21 to 28; 5 women, age 19 to 27) were instructed to exercise two days per week for 10 weeks. Each subject was told to adjust his/her running speed to 80% maximum heart rate. A mechanically-braked cycle ergometer was used before and after training for loading, and the heart rate was recorded. After 12 min of supine resting, all subjects were instructed to exercise on the bicycle for 10 min. Steady state exercise was set at a 50 rpm (40W) load. The power spectrum of heart rate variability was computed using the fast Fourier transform (FFT). Blood samples were obtained from the subjects before and after training. After training, low frequency (LF) power and LF/HF significantly decreased, while high frequency (HF) power significantly increased during exercise. Blood analysis revealed a significant decrease in red blood cell count (RBC), hemoglobin concentration (HGB), and hematocrit concentration (HCT) after training. The present results indicate that moderate exercise can lead to improvement in the autonomic nervous balance in non-athletes