[Approximate entropy analysis of changes in heart rate dynamics associated with aerobic training]

To elucidate the effects of aerobic training on heart rate dynamics, heart rate variability (HRV) of eight students before and after a six-month aerobic training and HRV of six athletes, were analyzed with conventional time and frequency domain methods as well as with the approximate entropy(ApEn). The results showed that after a six-month aerobic training, heart rate ApEn significantly decreased (P < 0.01, P < 0.05) during both supine control and -6.67 kPa/30 min lower body negative pressure (LBNP). The heart rate ApEn of the athletes during supine control and early stage of LBNP testing was significantly lower (P < 0.01, P < 0.05) than that of the students before training. It was found that the values of ApEn were negatively correlated with the duration of LBNP in the student group (P < 0.01). However, both the time and frequency domain analyses were unable to detect the aforementioned changes. The results suggest that aerobic training can decrease the complexity of heart rate dynamics, and the synchronization in heart rate control during LBNP is probably a sustained process.