Effects of endurance training and detraining on cardiac autonomic nervous system activity in young males

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 (V̇O₂max), 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∼0.50Hz) and the ratio of the low frequency power (LF : 0.04∼0.15 Hz) to the HF (LF/HF), respectively. The V̇O₂max 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 increased 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 detraining : 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 enhances 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.