Heart rate responses and oxygen consumption during Tai Chi Chuan practice
Abstract: Tai Chi Chuan (TCC) is a popular Chinese conditioning exercise, however, its exercise intensity remains controversial. The objective of this study was to determine the exercise intensity of Yang TCC by measuring heart rate (HR) responses and oxygen consumption (V[O.sub.2]) during practice. Fifteen men aged 39.9 [+ or -] 9.5 yrs (range 26-56 yrs) participated in this study. Subjects had practiced classical Yang TCC for 5.8 [+ or -] 2.4 years. HR responses and V[O.sub.2] were measured during practice of TCC by using a K4 telemetry system. Blood lactate was measured before and immediately after TCC practice. Additionally, breath-by-breath measurement of cardiorespiratory function and sequential determination of blood lactate were performed during the incremental exercise of leg cycling. Measurements obtained during the TCC practice and exercise testing were compared to determine the exercise intensity of TCC. While performing TCC, the mean HR of subjects was 140 [+ or -] 10 bpm, and the mean V[O.sub.2] was 21.4 [+ or -] 1.5 mL*[kg.sup.-1][min.sup.-1]. Compared with the data of the exercise test, the HR during practice was 58% of the heart rate range. Meanwhile, the V[O.sub.2] during TCC practice was 55% of the V[O.sub.2peak]. Additionally, the level of blood lactate immediately after TCC practice was 3.8 mM, which reflected the level of lactate during TCC, approximated the onset of blood lactate accumulation (OBLA). The results demonstrate that TCC is an exercise with moderate intensity, and is aerobic in nature.
Tai Chi Chuan, a branch of traditional Chinese martial arts, has been widely practiced since the 17th century. During its development, TCC gradually evolved into many styles. Among them the Chen’s style is the oldest, while the Yang’s style is the most popular. Classical TCC consists of many complex postures, and performing a complete set takes 20 to 30 minutes. In 1956, a simplified form of TCC was developed to facilitate promotion (China Sports, 1983). Simplified TCC consists of fewer postures and takes only five minutes to perform. Although simplified TCC is easier to learn, it may have lesser training benefits owing to the reduction of exercise intensity and duration.
Recent studies have shown that TCC can improve cardiorespiratory function (Lan et al., 1998; Lan et al., 1996; Lai et al., 1995), muscle strength (Lan et al., 1998) and balance (Tse et al., 1992; Wolf et al., 1997; Wolfson et al., 1996), as well as reducing blood pressure (Young et al., 1999) and the risk of falls (Wolf et al., 1996). Additionally, TCC can improve cardiorespiratory function in patients with coronary artery bypass grafting surgery (Lan et al., 1999). However, the exercise intensity of TCC remains controversial. Some studies only used several TCC postures for training (Wolf et al., 1996; Young et al., 1999), and the intensity and training effect might not be equal to a complete set of TCC. We believe that TCC-like calisthenics may have some benefits, but can not substitute for a complete set of TCC. From the perspective of exercise prescription, the intensity of standard TCC should be determined to facilitate the application of this exercise among different populations. To our knowledge, no study has continuously measured the HR responses and V[O.sub.2] of TCC. The purpose of this study was to determine the exercise intensity of the classical form of Yang TCC by simultaneously measuring the HR responses and V[O.sub.2] during the performance. Lactate response before and immediately after TCC practice was also measured.
Subjects and Methods
Subjects and Study Design
Subjects who had practiced Yang TCC for at least one year were recruited from a TCC club, with those who had a history of significant cardiovascular, pulmonary, metabolic, and musculoskeletal diseases being excluded. A total of 15 men were selected following the screening process. HR responses and V[O.sub.2] were measured by telemetry during the performance of TCC, and blood lactate was measured before and immediately after the TCC practice. Afterwards, subject underwent a maximal exercise test with gas analysis, and sequential measurements of blood lactate were obtained during this test. The Human Research Committee of the National Taiwan University Hospital approved this study. The procedures were fully explained to all subjects, and informed consents were obtained.
Tai Chi Chuan Training
Subjects practiced classical Yang TCC at least three times weekly. Each session included 20 minutes of warm up (low back and hamstrings stretching, gentle calisthenics and balance training), 24 minutes of TCC practice, and 10 minutes of cool down. Each set of TCC included 108 postures, with some repeated sequences. During the TCC practice, subjects were led by a Tai Chi instructor and imitated the motions and postures at the same speed. Subjects performed each posture according to a prerecorded form sequence on tape to ensure the same time course.
Measurements during TCC Practice
While performing TCC, subjects were fitted with K4 telemetry equipment (Cosmed s.r.l., Rome, Italy). The Cosmed K4 system consists of a photoelectric turbine flowmeter attached to a face mask. The flowmeter calculated the minute ventilation and measured the number of expiratory cycles per minute. A capillary tube conveyed expired air sampled from the turbine to the oxygen and carbon dioxide sensor in the transmitter unit for measuring FE[O.sub.2] and FEC[O.sub.2]. Before measurement, the turbine flowmeter was calibrated using a three liter calibration syringe. The oxygen analyzer was calibrated with room air that was assumed to contain 0.209 [O.sub.2]. The carbon dioxide analyzer was calibrated with room air of 0.03 C[O.sub.2]. Heart rates were measured via a Polar transmitter (Polar Electro, Port Washington, NY) secured to the chest.
Before the TCC practice, a 22-gauge intravenous catheter was inserted into the antecubital vein. An intermittent injection cap was then fastened to the indwelling catheter and secured to the forearm. Venous blood samples were taken before exercise, and at 1, 3, and 5 min after exercise, thus avoiding any interference with the TCC practice. Blood lactate concentrations were analyzed later with the sequential blood samples taken during the exercise test.
Measurements during Exercise Test
Maximal exercise testing was conducted for all subjects. Cigarette smoking and consumption of caffeinated beverages were forbidden on the morning of the test. The resting heart rate and blood pressure were recorded after sitting quietly for five minutes. Afterwards, each subject performed a continuous incremental bicycle exercise test with a pedaling rate of 60 [+ or -] 10 rpm until intolerable dyspnea or muscular fatigue occurred. The workload was increased by 10 watts every minute. Blood pressure was measured before the test and upon termination of the exercise.
A cycle ergometer (Erich Jaeger, Ergotest, Wuerzburg, Germany) was used for the test. The expired air was measured and analyzed breath-by-breath using an automated system (Cosmed s.r.l., B2 system, Rome, Italy). The exercise test was conducted in an air-conditioned laboratory with atmosphere temperature of 18 to 22 [degrees] C, barometric pressure of 757 to 768 mmHg, and relative humidity of 50 to 65%. Twelve-lead Electrocardiography was continuously monitored during the exercise. Cardiorespiratory parameters including heart rate, minute ventilation (VE), oxygen uptake, carbon dioxide production (VC[O.sub.2]), were continuously measured. The peak oxygen uptake (V[O.sub.2peak]) was defined as the highest attained [O.sub.2] during the exercise testing. The data were averaged every minute for further analysis.
The ventilatory threshold (VET) was determined by using at least two of the following criteria: 1) the VE/V[O.sub.2] began to increase systematically without a corresponding increase in the VE/VC[O.sub.2] (Davis et al., 1979), 2) the [P.sub.ET][O.sub.2] began to increase without a decrease in the [P.sub.ET]C[O.sub.2] (Davis et al., 1979), 3) departure from linearity for minute ventilation (Wasserman et al., 1973). Two independent observers, who were experienced in cardiopulmonary exercise testing, reviewed the determination of the VeT. If interobserver variations existed in determining the VeT, a third observer would be invited to examine the data. If an agreement could not be made between at least two evaluations, the data was deleted from the study.
Venous lactate and gas exchange data were simultaneously measured during the exercise testing. Venous blood samples were taken at rest; at 3, 6 min and thereafter every 1 min during exercise until exhaustion. To minimize the effects of muscular contraction on lactate measurement, subjects were instructed to minimize involvement of the upper extremities during exercise. Blood samples were analyzed with a lactate analyzer (Analox Instruments, London, England) using an enzymatic method that employs oxidation of lactate to pyruvate. The point of onset of blood lactate accumulation (OBLA) was defined as a level equal to 4.0 mM during the systemic increase of lactate.
Results
Fifteen men aged 39.9 [+ or -] 9.5 yrs (range 26-56 yrs) participated in this study. The subjects had been practicing classical Yang TCC for 5.8 [+ or -] 2.4 years, with an average frequency of 4.9 [+ or -] 1.2 times weekly. The group contained no smokers, and no subject had hypertension or diabetes mellitus. None of the subjects experienced angina, major ventricular arrhythmias or significant myocardial ischemia during the exercise testing.
Table 1 lists demographic data and peak cardiorespiratory variables obtained during the exercise testing. In the peak exercise, the mean peak HR of subjects was 186 [+ or -] 8 bpm, and the V[O.sub.2peak] was 39.1 [+ or -] 7.7 mL*[kg.sub.-1][min.sub.-1]. Table 2 shows the cardiorespiratory variables at the ventilatory threshold and during the TCC practice. At the ventilatory threshold, subjects’ HR was 135 [+ or -] 9 bpm, and the V[O.sub.2] was 22.5 [+ or -] 3.3 mL*[kg.sub.1][min.sub.-1]. During the TCC practice, the mean HR was 140 [+ or -] 10 bpm and the V[O.sub.2] was 21.4 [+ or -] 1.5 mL*[kg.sub.-1][min.sub.-1]. Because the resting HR of subjects was 76 [+ or -] 7 bpm, and the peak HR during exercise testing was 186 [+ or -] 8 bpm, the HR of subjects during TCC was 58% of their heart rate range (HRR = peak HR - resting HR). Meanwhile, the V[O.sub.2] while performing TCC was 55% of their V[O.sub.2peak].
Figure 1 illustrates the heart rate responses during the TCC practice. During the performance of TCC, subjects’ HR increased rapidly during the first 12 minutes, and then increased slowly towards the end of exercise. Figure 2 illustrates the evolution of V[O.sub.2] during the TCC practice. Subjects’ V[O.sub.2] demonstrated a sharp increase in the first three minutes, and then it achieved a steady-state towards the end of exercise.
[FIGURES 1-2 OMITTED]
Subject’s blood lactate concentration maintained its resting level until 110 watts, then gradually increased towards the end of exercise. Meanwhile, blood lactate level during recovery was 8.4 [+ or -] 1.2, 8.6 [+ or -] 1.1 and 8.4 [+ or -] 1.3 mM at 1, 3, 5 min after exercise, respectively. Furthermore, blood lactate concentration after TCC practice was 3.8 [+ or -] 0.6, 3.6 [+ or -] 0.7 and 3.0 [+ or -] 0.6 mM at 1, 3, 5 min, respectively, after the termination of TCC.
Discussion
Previous reports indicated that the exercise intensity of TCC varies among different styles (Brown et al., 1989; Gong et al., 1981; Lan et al., 1996; Zhuo et al., 1984). Zhou and associates (1984) reported a heart rate of 134 bpm in 11 young men while practicing classical Yang TCC. In the present study, the mean HR of 15 men aged 39.9 [+ or -] 9.5 yrs, while performing classical Yang TCC, was 140 bpm. As for the older subjects, we have previously reported that the mean HR of subjects aged 50 to 65 yrs approximated 130 bpm during TCC practice, and 120 bpm for subjects aged 65 to 80 yrs (Lan et al., 1996). In comparison with the HR data, the relative exercise intensity seems similar among different age groups while performing classical TCC. During the performance of simplified TCC, Gong et al. (1981) reported that the heart rate in subjects aged 48 to 80 was only 104 bpm. The data indicates that the exercise intensity of simplified TCC is lower than that of the classical form. This is likely owing to the fact that the simplified form comprises fewer postures and excludes strenuous movements. Brown and colleagues (1989) have reported that the mean HR of six young men was only 117 bpm while performing Yang TCC. However, they only collected variables at 7, 14, and 21 minutes during TCC practice, and the HR might drop while measuring the data. We believe that continuous monitoring of HR and V[O.sub.2] is an appropriate way to determine the intensity of TCC.
This study used the K4 system to measure V[O.sub.2] and HR responses simultaneously during TCC practice. The K4 system contains an O2 and CO2 electrode and weighs only 850 g, so it will not hinder movement of TCC. Additionally, the K4 system is accurate for V[O.sub.2] measurements from rest to maximum exercise levels (Hausswirth et al., 1997). During TCC practice, the mean V[O.sub.2] was 21.4 mL*[kg.sub.-1][min.sub.-1], and the mean HR was 140 bpm. Compared with the data obtained during the exercise testing, the HR while performing TCC was 58% of subjects’ heart rate range, and this value approximated to their HR at the ventilatory threshold. Furthermore, the V[O.sub.2] while performing TCC was 55% of subjects’ V[O.sub.2peak], and it was also close to the V[O.sub.2] at the ventilatory threshold.
Since the mean V[O.sub.2] while performing TCC achieved a steady-state after three minutes of practice (Figure 2), the blood lactate concentration immediately after TCC practice might reflect the level of lactate during the exercise. The blood lactate concentration was 3.8 mM on termination of TCC, and it approximated the OBLA. Because the OBLA implies the maximum exercise intensity a person can sustain over a prolonged period, the exercise intensity during TCC practice appears appropriate for those subjects. Therefore, although Zhou et al. (1984) contended that the intensity of classical TCC was insufficient to improve cardiorespiratory fitness, our data demonstrated that this exercise might benefit the cardiorespiratory function. According to our previous investigation, 12 months of TCC training could significantly enhance the aerobic power of healthy older individuals. (Lan et al., 1998). Furthermore, one year of TCC training also benefited the cardiorespiratory function of patients with coronary artery bypass grafting (Lan et al., 1999).
TCC has several unique characteristics. First, the motions of TCC are slow, harmonious and relaxing. Subjects practice TCC in body motions that are well coordinated and continuous throughout the exercise. Second, TCC is performed in a semi-squatting posture at extremely slow speed. During the performance, various degrees of concentric and eccentric contraction are demanded for lower extremities (Lan et al., 2000). Third, TCC is an exercise with low impact, low velocity, and with minimal orthopedic complication (Kirsteins et al., 1991). From the perspective of exercise prescription, TCC is a suitable conditioning exercise because the training characteristics fulfill recommendations of the American College of Sports Medicine (ACSM, 1998) regarding exercise to develop and maintain cardiorespiratory fitness. Moreover, TCC is a low technology approach to conditioning, which can be implemented in the community at a minimal cost.
In conclusion, this study has demonstrated that the exercise intensity of TCC was 55% of subjects’ V[O.sub.2peak], and 58% of their heart rate range. The results indicate that TCC is an exercise with moderate intensity, and is aerobic in nature. Individuals who regularly practice TCC may improve the exercise capacity and promote their health.
Table 1. Physical Characteristics and
Peak Cardiorespiratory Variables of Subjects
Age (yr) 39.9 [+ or -] 9.5
Body Height (cm) 171.0 [+ or -] 6.2
Body Weight (kg) 67.8 [+ or -] 13.9
V[O.sub.2peak] (ml*[kg.sup.-1]*[min.sup.-1]) 39.1 [+ or -] 7.7
H[R.sub.peak] (beats [min.sup.-1]) 186 [+ or -] 8
Peak [O.sub.2] pulse (mL*[beat.sup.-1]) 13.9 [+ or -] 2.5
V[E.sub.peak] (l*[min.sup.-1]) 95.6 [+ or -] 18.0
RER 1.17 [+ or -] 0.08
W[R.sub.peak] (watt) 217 [+ or -] 39
V[O.sub.2]:[O.sub.2] consumption; HR: heart rate; RER: respiratory
exchange rate; VE: minute ventilation; WR: work rate
Table 2. Cardiorespiratory Variables at the Ventilatory Threshold
and during Tai Chi Chuan Practice
Ventilatory Threshold
V[O.sub.2] (mL*[kg.sup.-1]*[min.sup.-1]) 22.5 [+ or -] 3.3
HR (beats*[min.sup.-1]) 135 [+ or -] 9
[O.sup.2] pulse (mL*[beat.sup.-1]) 11.7 [+ or -] 1.8
VE (l [min.sup.-1]) 39.2 [+ or -] 8.0
TCC Practice
V[O.sub.2] (mL*[kg.sup.-1]*[min.sup.-1]) 21.4 [+ or -] 1.5
HR (beats*[min.sup.-1]) 140 [+ or -] 10
[O.sup.2] pulse (mL*[beat.sup.-1]) 10.5 [+ or -] 0.7
VE (l [min.sup.-1]) 37.8 [+ or -] 4.3
V[O.sub.2]:[O.sub.2] consumption; HR: heart rate; VE: minute
ventilation
Acknowledgment
The authors would like to thank Professor S.H. Tang (School of Physical Education of National Taiwan Normal University) for his assistance in training those TCC practitioners who participated in this study.
by Ching Lan, Ssu-Yuan Chen, Jin-Shin Lai, May-Kuen Wong