Tai chi has been claimed to generate beneficial effects with respect to a wide range of diseases. The purpose of this systematic review was to evaluate evidence from randomised clinical trials (RCTs) testing the effectiveness of tai chi for increasing aerobic capacity. Systematic searches were conducted on 14 electronic databases without restrictions on population characteristics or the language of publication. The outcome measures considered for inclusion were changes in maximal oxygen consumption as a test for aerobic capacity. Five RCTs met all inclusion criteria. Three RCTs compared the effects of tai chi with no treatment. The meta-analysis failed to show an effect of tai chi on aerobic capacity compared with sedentary controls (n = 151, weight mean difference, ml/kg/min, 0.50, 95% CI −1.14 to 2.15, p = 0.55). Two RCTs compared tai chi with conventional physical exercise including brisk, low intensity and moderate intensity walking, and aerobic exercise. The results show that tai chi was not statistically significantly superior to physical exercise. In conclusion, the existing evidence does not suggest that regular tai chi is an effective way of increasing aerobic capacity.
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Maximal oxygen uptake or consumption is an important determinant of endurance performance, which represents a measure of cardiovascular capacity for an individual at a given degree of fitness and oxygen availability.1 It is also an independent risk factor for all-cause and cardiovascular disease mortality.2
Tai chi is a form of complementary therapy with similarities to aerobic exercise which, according to some of its proponents, improves cardiovascular fitness.12 It comprises a series of postures linked by gentle and graceful movements.3
Several reviews have suggested that tai chi is beneficial for improving cardiorespiratory function including aerobic capacity.4567 However, these reviews had several limitations, such as no systematic approach and the use of meta-analysis despite statistical and clinical heterogeneity of the primary data. The value of tai chi as a means of improving aerobic capacity therefore remains uncertain. The aim of this systematic review is to clarify this issue by critically evaluating all RCTs of tai chi for improving aerobic capacity.
Electronic databases were searched from their respective inceptions through July 2008 using the following databases: MEDLINE, CINAHL, EMBASE, The Cochrane Library 2008, Issue 3, six Korean medical databases (Korean Studies Information, DBPIA, Korea Institute of Science and Technology Information, Research Information Center for Health Database, KoreaMed, and Korea National Assembly Library) and four Chinese databases (China Academic Journal, Century Journal Project, China Doctor/Master Dissertation Full text DB, China Proceedings Conference Full text DB). The search terms used were based around two concepts. Concept one included all terms for tai chi and concept two included terms for aerobic capacity. Two concepts were combined using the Boolean operator AND. Korean and Chinese terms for tai chi and aerobic capacity were used in the Korean and Chinese databases. In addition, our own files and our review journal (FACT—Focus on alternative and complementary therapies, from 1996 to 2008) were manually searched. The references of all located articles and the proceedings of the first International Conference of Tai Chi for Health (December 2006, Seoul, South Korea) were hand-searched for further relevant articles.
All prospective randomised clinical trials (RCTs) of tai chi including the outcome measures of aerobic capacity were included. There were no restrictions on population characteristics. No language restrictions were imposed. Dissertations and abstracts were included. Hardcopies of all articles were obtained and read in full.
Data extraction and quality assessment
Data were extracted systematically in a predefined, standardised manner according to design, number of subjects, and treatments for intervention and control groups (table 1). The Jadad score was calculated by assessing three criteria: description of randomisation, blinding and withdrawals; the score ranges from a minimum of 0 to a maximum of 5 points.89 Taking into account that patients and therapists are virtually impossible to blind to tai chi, one point was given if the outcome assessor was blinded. Allocation concealment was assessed using the Cochrane Collaboration’s classification.10 Selection, data extraction and quality assessment were performed independently by two reviewers (MSL, ENL). Discrepancies were resolved by discussion between two reviewers (MSL, ENL) and if needed, by seeking the opinion of the third reviewer (EE).
The mean change of maximal oxygen consumption compared with baseline was used to assess the differences between the intervention groups and the control groups. Weight mean differences (WMD) and 95% confidence intervals (CI) were calculated using the Cochrane Collaboration’s software (Review Manager (RevMan) V.5.0 for Windows, The Nordic Cochrane Centre, Copenhagen, Denmark). The variance of the change was imputed using a correlation factor of 0.5.11 We then pooled the data across studies using a random effects model. The χ2 test and the Higgins I2 test were used to assess heterogeneity.
The searches identified 43 potentially relevant articles, of which 37 were excluded. The excluded articles referred to six non-RCTs, six trials without a control-group, nine cross-sectional studies, two duplicate studies, 13 non-clinical trials and two trials unrelated to tai chi. Six RCTs met our inclusion criteria. The key data are summarised in table 1.121314151617 Five trials originated from the USA1213141617 and one trial was conducted in Korea.15 One RCT failed to mention the type of tai chi employed,12 four employed the yang style tai chi13141617 and one employed the sun style.15 The studies varied in duration from 12 to 16 weeks. The number of tai chi sessions ranged from 24 to about 48. The number of supervised interventions ranged from two to three sessions weekly. The session duration ranged from 60 min to 90 min per session. Four of the included trials adopted a two-armed parallel-group design,14151617 one was a three-armed parallel group design13 and one was a five-armed trial.12 Three of the included RCTs used a cycle ergometer test,131415 one employed maximal graded walking treadmill test,12 one used bicycle a ramp protocol16 and one employed six minute work protocol.17
The methodological quality of the RCTs was high on average (average Jadad score = 3.2 (1.2)). Five RCTs described the methods of randomisation.1314151617 Details of drop-outs and withdrawals were described in five trials.1314151617 Three reported details about allocation concealment with adequate methods.151617 Three RCTs adopted assessor blinding for measurement for VO2max.131416 Adverse events were mentioned in two studies.1617
Tai chi versus sedentary group
Three RCTs compared the effects of tai chi with usual life style or usual care.121516 The meta-analysis failed to show the effect of tai chi for aerobic capacity compared with sedentary controls (n = 151, WMD, ml/kg/min, 0.50, 95% CI −1.14 to 2.15, p = 0.55; heterogeneity: τ2 = 0.00, χ2 = 1.50, p = 0.68, I2 = 0%, fig 1A). There was no difference between the random effect model and the fixed effects model. One RCT compared tai chi with psychosocial support therapy in breast cancer patients and failed to show superiority of tai chi.17
Tai chi versus physical exercise
Three RCTs compared tai chi with conventional physical exercise, that is, brisk, low intensity and moderate intensity walking and aerobic exercise.121314 Pooling the results of these RCTs together, that the overall effect of tai chi on aerobic capacity was not statistically significantly superior to conventional physical exercise (n = 175, WMD, −1.01, 95% CI −3.56 to 1.54, p = 0.44) although marked heterogeneity was observed in this model (τ2 = 7.00, χ2 = 17.58, p = 0.004, I2 = 72%, fig 1B). Subgroup analysis also failed to show beneficial effects of tai chi compared with walking exercises, but there was high heterogeneity in this data set (n = 113, WMD, −1.19, 95% CI −4.59 to 2.21, p = 0.49, heterogeneity: τ2 = 11.37, χ2 = 17.49, p = 0.002, I2 = 77%, fig 1C).1213
Only few rigorous trials have tested the effects of tai chi on aerobic capacity. In comparison to sedentary controls, the results failed to show any effects of tai chi. Comparing tai chi to physical exercise, the data failed to suggest that tai chi is superior to conventional exercise. Whether these findings reflect equivalence of effect or ineffectiveness of tai chi is as yet unclear. Overall our findings provide no convincing evidence that tai chi is beneficial for improving aerobic capacity.
We assessed the methodological quality of the primary studies using a modified Jadad scale. It allocates one point for subject blinding and assessor blinding separately. Considering difficulty for patients blinding, most of the trials (except one) have higher methodological quality. The concealment of treatment allocation was reported in three trials.141516 Trials with inadequate blinding and inadequate allocation concealment may be subject to selection bias and are likely to generate exaggerated treatment effects.18 Details of drop-outs and withdrawals were described in five trials.1314151617 One of the included trials, which only reported favourable effects of tai chi compared with brisk walking, was burdened with a small sample size.13 Single small trials, even if performed impeccably, can give the wrong result because of random play of chance.19
A potential weakness of measuring maximal oxygen uptake during longitudinal training studies is its sensitivity to methodological details.2021 Several methods were employed to measure the maximal oxygen uptake in the RCTs included in this review. Two of the RCTs employed direct measurements of maximal oxygen uptake,1216 while others used indirect method. Direct measurement provides a better estimate of maximal oxygen uptake. Three RCTs,131415 which employed submaximal exercise testing, used the results to predict maximal oxygen uptake from the heart rate-workload relationship. Although measurement procedures cannot account for the intergroup differences reported, it may have contributed to the variability of the data.
The fact that there is no good evidence could be due to tai chi being ineffective or to the fact that it was not practiced properly. One possibility is that treatment periods could have been too short to generate significant effects. Previous analysis with cross-sectional studies showed that longer practice of tai chi is beneficial for aerobic capacity compared with short period participating.22 Consequently, the duration and the frequency of tai chi practice may be important. Furthermore, the type of tai chi employed is relevant. There are significant differences between the numerous variations of tai chi, and so a clear description of the tai chi intervention should be provided together with a description of the level of expertise of the instructors.2324
Limitations of our systematic review, and indeed systematic reviews in general, pertain to the potential incompleteness of the evidence reviewed. In this review, there were no restrictions in terms of publication language and a large number of different databases were searched. Selective publishing and selective reporting are other major causes for bias, which have to be considered.2526 These biases might have changed the meta-analytic result. Another limitation is the paucity and often suboptimal quality of the studies. Furthermore, we did not consider including other indicators of aerobic fitness including lactate, ventilatory thresholds and physical walking capacity.
In conclusion, the evidence that tai chi might improve aerobic capacity is not convincing. Whether the finding of no difference compared with exercise reflects equivalence of effects is yet unclear. Currently there are few good quality trials More rigorous RCTs, with larger sample sizes and longer treatment periods are required if we want to determine whether tai chi improves aerobic capacity.
What is already known on this topic
Tai chi is a form of complementary therapy with similarities to aerobic exercise that improves cardiovascular fitness.
Tai chi is beneficial for improving cardiorespiratory function including aerobic capacity.
What this study adds
The evidence that tai chi might improve aerobic capacity is not convincing.
Whether the finding of no difference compared with exercise reflects equivalence of effects is unclear.
Funding MSL was supported by Korea Institute of Oriental Medicine (K08010). The study sponsor had no involvements in study design; in the collection, analysis and interpretation of data, in the writing of the report or in the decision to submit the paper for publication.
Competing interests None.
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