Abstract
The effects of endurance training and detraining on cardiac autonomic nervous system activity were studied by using the power spectral analysis of heart rate (HR) variability. Twenty-one sedentary male subjects were trained for 8 weeks using cycle ergometer exercise [70% of maximal oxygen uptake (VO2max), 60 min, 3.4 times/wk] . Resting HR for 5 min was recorded before the training, after the 8-week training period, and after the 2-week and 4-week detraining period. The indices of cardiac parasympathetic and sympathetic nervous system activity were determined by Mem-Calc method, as the high frequency power (HF : 0.15-0.50 Hz) and the ratio of the low frequency power (LF : 0.04-0.15 Hz) to the HF (LF/HF), respectively. The VO2max after the training and 4 weeks detraining period were significantly higher than the initial value (before training : 41 ± 1 ml/kg/min ; after training: 48±2, P<0.0001; after detraining: 46±2, P<0.001) . The HF was significantly in-creased by the training (P<0.05), and maintained the increased level for the 2-week detraining period (before training : 6.4±0.3 In ms2; after training: 7.0±0.2, P<0.01; after 2-week detrain-ing: 7.0±0.2, P<0.05) . The increase in the HF, however, disappeared after the 4-week detraining period (6.8±0.31n ms2) . The LF/HF did not show any significant changes during the training and detraining period. These results suggest that an endurance exercise with moderate intensity enhan-ces cardiac parasympathetic nervous system activity, but not cardiac sympathetic nervous system activity. The enhanced cardiac parasympathetic nervous system activity, however, may regress rapidly during detraining period.
