心率的快慢受竇房結節律細胞的基本發電頻率和自律神經系統的調控這兩個主要因素影響。竇房結節律細胞的基本發電頻率是固定的，並不會在短時間內改變，而自律神經系統的活性則無時無刻不在變化，以因應身體的需要。竇房結放電頻率因自律神經系統的調控而表現出的變異度即為心率變異度。將心率的訊號作快速傅立葉轉換，就可得心率的功率頻譜圖，在功率頻譜圖上通常可以發現兩個明顯的波峰，即在0.15到0.40赫茲的高頻處有由副交感神經調控的波峰，以及在0.04到0.15赫茲處有由副交感神經及交感神經共同調控的低頻波峰。一般以高頻功率比（＝100 ×高頻功率/總功率）做為副交感神經活性的指標，以低頻功率比（＝100 ×低頻功率/總功率）做為交感與副交感神共同調控的指標，且以低高頻功率比（＝ 低頻功率/高頻功率）做為交感－副交感神經活性平衡的指標。
在太極拳的研究方面，我們邀請二十名打太極拳及二十名對照組參與本研究，我們比較兩組參與者心率變異度、血流動力學及肺功能的差異，以及太極拳運動後心率變異度的變化情形。結果顯示太極拳組運動前的總功率、極低頻功率、低頻功率、低頻功率比及低高頻功率比都顯著地大於對照組，而心跳速率、收縮壓及舒張壓則沒有差異。太極拳組在太極拳運動後，高頻功率比從運動前的22.8 ± 14.6 nu 上升到運動後30分鐘的28.2 ± 16.1 nu，運動後60分鐘又持續又上升到30.6 ± 18.4 nu。相反的，低高頻功率比則由運動前的2.5 ± 2.4 下降到運動後30分鐘的1.8 ± 1.4 ，以及運動後60分鐘的2.2 ± 2.9。心跳速率、收縮壓、舒張壓、平均動脈壓及脈壓於運動後都顯著地下降。這些數據顯示太極拳的短期效應是提升副交感神經的活性，並使得交感神經的活性下降，故太極拳值得被推荐給中老年人，作為一種健身運動。
在外丹功方面，有二十名的外丹功組及二十名的對照組參與本研究。我們比較兩組參與者心率變異度、血流動力學及肺功能的差異，以及外丹功運動後心率變異度的變化情形。結果顯示外丹功組運動前的心跳間期標準偏差與變異係數、總功率、低頻功率及低頻功率比都顯著地大於對照組。外丹功組在外丹功運動後，高頻功率比從運動前的27.7 ± 13.2 nu 上升到運動後30分鐘的37.6 ± 16.0 nu，運動後60分鐘又持續又上升到39.8 ± 20.1 nu。相反的，低高頻功率比則由運動前的1.3 ± 1.0 下降到運動後30分鐘的1.0 ± 0.9 ，運動後60分鐘持續下降到0.8 ± 0.6。這些數據顯示外丹功的短期效應是提升副交感神經的活性，並使得交感神經的活性下降；外丹功的長期效應是增加交感神經的活性，而不影響副交感神經的活性。，外丹功值似得被推荐給中老年人作為一種健身運動。
Aging and many diseased states have been shown by heart rate variability (HRV) analysis to be associated with depressed vagal activity. The extent of vagal depression correlated with the severity or poor prognosis of the disease. Methods that can increase the vagal modulation of the subjects have been a goal of clinician. Health promotion and disease prevention have become increasingly important to the public and health professionals since 1990s. Good nutrition and regular exercise can reduce the risk of various kinds of diseases, and may extend the duration of life for many people, thereby serving as the best current prescription for a long and healthy life. Tai Chi Chuan (TCC) and Wai Tan Kung (WTK) are two very popular and distinct conditioning calisthenics in Oriental countries. Both TCC and WTK are claimed to be suitable for older people and patients with chronic diseases. The aim of this study was to investigate the effects of TCC and WTK on the autonomic nervous modulation in the aged subjects, and to compare the physiological effects of TCC and WTK.
The heart rate is modulated by the sinus node in the heart, and the autonomic nervous system in the body. The electrical rhythm of the sinus node within the heart is relatively fixed, but the autonomic nervous activity is changed from time to time to maintain the physiological function of the body. The heart rate variability is the variability in the firing of the sinus node that is modulated by the autonomic nervous system. The heart rate variability as studied by power spectral analysis can then be used as a tool to evaluate the activity of the autonomic nervous system. The power spectrum of the heart period obtained by means of fast Fourier transformation usually demonstrates two significant groups of peaks. The vagally mediated high frequency groups of peaks are located within 0.15-0.40 Hz. The noemalized high-frequency power (high-frequency power/total power) is usually used as the index of vagal modulation, the noemalized low-frequency power (low-frequency power/total power) as the index of sympathetic and vagal modulation, and the low-/high-frequency power ratio (low-frequency power/high-frequency power) as the index of sympathovagal balance.
Twenty TCC practitioners and twenty normal controls were included in the first study. The stationary state spectral heart rate variability (HRV) measures, hemodynamics and spirometry between TCC practitioners and normal controls, and the sequential changes in HRV measures after classical Yang”s TCC were compared. The total power (TP), very low frequency power (VLFP), low frequency power (LFP), normalized low-frequency power (nLFP) and low-/high-frequency power ratios (LFP/HFP) in TCC practitioners were all significantly higher than those of normal controls, whereas the heart rate (HR) and systolic (SBP) and diastolic blood pressures (DBP) were not different between these two groups of subjects. After TCC, the nHFP increased significantly from 22.8 ± 14.6 normalized units (nu) before TCC to 28.2 ± 16.1 nu 30 min after TCC and to 30.6 ± 18.4 nu 60 min after TCC. In contrast, the LFP/HFP decreased significantly from 2.5 ± 2.4 before TCC to 1.8 ± 1.4 30 min after TCC and to 2.2 ± 2.9 60 min after TCC. The HR, SBP, DBP, mean arterial blood pressure (MABP), and pulse pressure (PP) also decreased sequentially after TCC. It is evident that the short-term effect of TCC was to enhance the vagal modulation and tilt the sympatho-vagal balance toward deceased sympathetic modulation in older persons. TCC might be good health-promoting calisthenics for older persons.
In the second study, twenty WTK practitioners and twenty normal controls were recruited in this study. The stationary state spectral HRV measures, hemodynamics and spirometry between WTK group and normal controls, and the sequential changes in HRV measures and hemodynamics after WTK, were compared. We found that the standard deviation and coefficient of variation of RR intervals, TP, LFP, and nLFP in WTK practitioners before WTK were all significantly higher than those of normal controls. After WTK, the nHFP increased significantly from 27.7 ± 13.2 normalized unit (nu) before WTK to 37.6 ± 16.0 nu 30 minutes after WTK, and to 39.8 ± 20.1 nu 60 minutes after WTK. In contrast, the LFP/HFP decreased significantly from 1.3 ± 1.0 before WTK to 1.0 ± 0.9 30 minutes after WTK, and to 0.8 ± 0.6 60 minutes after WTK. We concluded that the short-term effect of WTK was to enhance the vagal modulation and to suppress the sympathetic modulation, whereas the long-term effect of WTK was to enhance the sympathetic modulation without compromising the vagal modulation of the elder adults. The WTK is a good health promotion calisthenics that can be recommended to the elder adults.
In the third study, thirty WTK practitioners, thirty TCC practitioners and thirty normal controls were included in this study. The hemodynamics, spirometry, and stationary state HRV measures among normal controls, WTK and TCC practitioners were compared. Before exercise, the percentage forced vital capacity (%FVC) of the TCC practitioners was significantly higher than that of WTK practitioners, and both nLFP and LFP/HFP of the TCC and WTK practitioners were significantly higher than those of normal controls. After WTK or TCC, while both nVLFP and LFP/HFP decreased significantly, the nHFP increased significantly. In addition, the SBP, DBP, MABP, PP and HR all decreased significantly after WTK or TCC. The SBP and MABP in the TCC practitioners 30 or 60 min after TCC were significantly lower than those of the WTK practitioners 30 or 60 min after WTK. It is evident that while the effect of TCC and WTK on the autonomic nervous modulation is comparable to each other, the TCC is superior to WTK in lowering the arterial blood pressure and improving the vital capacity in the elderly.
In conclusion, while the short-term effect of WTK on the autonomic nervous modulation is comparable to TCC, the short-term effect of TCC on lowering the blood pressure seems to be better than WTK, and the long-term effect of TCC on increasing the vital capacity seems to be better than WTK in the elderly. WTK and TCC are two good health promotion calisthenics that are worthy of recommending to the elderly in terms of their effects on the autonomic nervous modulation and cardiopulmonary functions.