Cardiac autonomic control immediately after exercise in female distance runners

The purpose of this study was to examine the timing of recovery of the high-frequency (HF) component of heart rate variability (HRV) after exercise in female distance runners using frequency analysis of HRV. Twenty-two female young (n=11; YG) and middle-aged (n=11; MG) distance runners participated in this study. The two groups performed incremental cycle exercise with progressive intensity until exhaustion. The R-R intervals were processed by the maximum entropy method for determination of HF power on successive 7-second segments of 70 seconds of the recovery period. In the YG, the HF power of the second 7-sec segment showed significantly higher values than the 7 sec before cessation of exercise (p<0.005), whereas the MG exhibited significantly higher values in the third segment (p<0.005). The YG indicated significantly higher HF power than the MG in the fifth segment (p<0.0045). These findings suggested the occurrence of parasympathetic reactivation at an earlier period compared to the previous findings. Multiple influences of various factors including the subjects' characteristics to HF recovery were suggested. However, the detection of the timing of HF recovery despite the duration of sharp change in HR indicated that HRV was an effective evaluation technique for determination of autonomic control immediately after exercise.