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Many studies and reviews have shown Tai Chi to be effective in improving balance in relatively healthy older people, but some studies who used the general healthy older population found no significant change in balance (Fong & Ng, 2006; Lelard, Doutrellot, David & Ahmadi, 2010; Woo et al., 2007) or no difference between groups (Lelard et al., 2010; Woo et al., 2007).

Randomization

A meta- analysis by Wu et al. (2018) found that three articles reviewed described the

method of randomization. One study reviewed fail to mention their method of randomization (Hart, Kanner, Giboa-Mayo, Haroeh-Peer & Rozenthul-Sorokin, 2004). Au-Yeung, Hui-Chan

& Tang, (2009) randomized participants with the aid of a computer program that treated gender and side of hemiplegia as stratification variables. Zeng et al. (2014) randomized their participants by using random number tables, where even numbers were allocated to the control group and odd numbers allocated to Tai Chi. Li et al. (2012) randomized participants using permuted-block randomization. Seven studies did not randomize participants (Burschka, Keune, Hofstadt-van Oy, Oschmann & Kuhn, 2014; Desrochers, Kairy, Pan, Corriveau & Tousignant, 2017; Hain, Fuller, Weil & Kotsias, 1999; Hakim, Kotroba, Teel, & Leininger, 2010; Kim, Kim & Lee, 2015; Li et al., 2007; Pan, Kairy, Corriveau & Tousignant, 2017). Hakim et al. (2010) comment that causation could, therefore, not be determined.

Nine of the nineteen studies reviewed by Chen et al. (2007) were not randomized, with Maciaszek and Osiński (2010) suggesting that studies without a control group were not reliable in terms of their results. The reviewers also questioned whether experimental and control groups were equal because some participants in studies were already experienced in Tai Chi at baseline (Tsang & Hui-Chan, 2005; Wong, Lin, Chou, Tang & Wong, 2001).

Therefore, it was difficult for the reviewers to assume groups within studies were

equivalent. Hakim et al. (2010) used a convenience sample, whereas Burschka et al. (2014) recruited via mail to patients who were or had been in out-patient care. Hackney and

Earhart (2008) used simple random assignment which was performed by the first author by tossing a coin. Kim et al. (2015) acknowledge that they randomly allocated participants into one of two groups but did not mention which method they used. Maciaszek and Osiński (2010) question the reliability of some of the results generated from the studies they reviewed. Participants also volunteered and were categorized into groups, limiting the generalizability of the findings. Li et al. (2007) acknowledge that a pre-test/post-test design was susceptible to uncontrolled threats to both internal and external validity. For example, Li et al. (2007) could not be sure that improvements made were directly related to Tai Chi because other confounding factors such as maturation, testing effect or selection bias may have influenced the outcomes.

Hwang et al. (2016) comment that their study may be biased due to the volunteer effect which may restrict generalization of results to frail elderly people. Participants were enthusiastic and may have had high expectations of Tai Chi (Li et al., 2007). Zeng et al.

(2014) comment that the Tai Chi group may have been influenced by positive effects from the group, such as receiving more attention from the Tai Chi instructor and social

interactions. Li et al. (2012) recognize awareness of group allocation may have introduced biases in the results, and the authors suggest that those interested in participating may have had positive expectations about the benefits of Tai Chi.

Intervention

Optimal training duration and most effective period of exercise were not established from the review by Maciaszek and Osiński (2010). Studies reviewed varied in duration. For example, some studies recommended 12 months (Pereira, Oliveira, Silva, Souza & Vianna, 2008; Woo et al., 2007), whereas others recommended eight weeks (Zhang et al., 2006).

Optimum intensity and frequency were also not established with the reviewers concluding that frequent training did not improve balance (Tsang et al, 2004). However, it is unclear whether participants included in the reviews by Jiménez-Martin et al. (2013) and Maciaszek and Osiński (2010) had balance impairments to begin with in order see an improvement.

Hackney and Earhart (2010) recognise that Tai Chi duration was short with the authors suggesting longer training may increase benefit from Tai Chi.

Home practice

Three studies encouraged home practice (Au-Yeung et al., 2009; Choi et al., 2013; Zeng et al., 2014), where one encouraged home practice to be done outside in a park or in nature (Zeng et al., 2014). Choi et al. (2013) only recommend home practice once a week,

whereas Au-Yeung et al. (2009) recommend three hours of home practice a week. Zeng et al. (2014) do not specify time. Burschka et al. (2014) specifically told participants not to practice at home because it would be unsupervised. Au-Yeung et al. (2009) encouraged home practice by offering a video clip of the lesson to be practiced. Home practice with a video and written materials was encouraged every day for 30 minutes. Hain et al. (1999) included home practice in their study but did not measure compliance. However, compliance with home practice was low, despite all participants continuing with Tai Chi after the study ended. The authors cite that the Tai Chi exercises may have been too difficult compared to the exercises given to the control group. Therefore, it is difficult to assess how this part of the programme contributed to the results. Adherence to home practice was advised by Zeng et al. (2014) who suggest a family member supervise this. The authors acknowledge that in China, families live together with their elderly to make this feasible. This supervisor may also have prevented any falls rather than the Tai Chi according to the authors.

Control group

Two studies offered stretching and breathing exercises to their control groups (Au-Yeung et al., 2009; Li et al., 2012). It is acknowledged by Li et al. (2012) that the control group participated in low-level exercise. The authors suggest that by using a non-exercise control group, the net gain of Tai Chi training can be gauged. Li et al. (2012) offered a third group

resistance training which included muscle training important for balance, whereas Zeng et al. (2014) used strength and hip ROM training. This training included bilateral lower-extremity strength training. The control groups in the studies by Li et al. (2012) and Zeng et al. (2014) cannot be compared to community physiotherapy because stroke survivors would not be receiving such intense training as part of their rehabilitation. Therefore, it cannot be confirmed if Tai Chi can supplement rehabilitation by comparing with such a control group.

Hakim et al. (2010) included two control groups; one that practised Yoga and one that did not engage in any exercise programme. However, intensity and duration of Yoga is not mentioned by the authors. Kim et al. (2015) involved general physiotherapy with both the Tai Chi group and the control group, suggesting that Tai Chi may be a supplement to the physiotherapy already being received. Hackney and Earhart (2008) do not include a control group in their study, and Choi et al. (2013) offered no exercise to their control group.

Adherence

Overall, adherence to Tai Chi among all studies was good. Out of 195 participants, 176 completed the study (Li et al., 2012). Five participants dropped out of Tai Chi and 11 dropped out of the control group (unrelated to the study) in Zeng’s study. Zeng et al.

(2014) commented that due to 40 per cent of participants dropping out, the sample size was reduced greatly. In contrast, Au-Yeung et al. (2009) acknowledge that the Tai Chi group had lower compliance than the control group. The authors suggest this was because the control group exercises were easier to learn and practice at home. To improve

adherence to Tai Chi, Au-Yeung et al. (2009) recommend forming Tai Chi groups in convenient community venues.

Hakim et al. (2010) do not mention adherence but participants had voluntarily enrolled in Tai Chi or Yoga prior to taking part in the study, as well as not seeming to have any chronic medical conditions. Therefore, adherence was good in the Tai Chi group (76.1 per cent) and Yoga group (54.5 per cent). Only 30 per cent completed in the no exercise group. Hackney and Earhart (2008) required their participants to attend at least 20 sessions over 13 weeks.

Four participants dropped out of Tai Chi (two for transportation reasons, one thought Tai Chi was not challenging, one was hospitalised). Three dropped out in the usual care group but no reason was given. Kim et al. (2015) and Burshka et al. (2014) do not mention attendance or drop-out rates.

Effectiveness of Tai Chi on balance

Jiménez-Martin et al. (2013) found that studies evaluated two types of balance: static and dynamic. Thirteen studies of the 27 reviewed by Jiménez-Martin et al. (2013) showed that

Tai Chi caused significant improvements in static balance. Kim et al. (2015) comment that improved static balance was due to improvement in proprioception of the trunk and lower limb. Further, control of muscle and joints was enhanced with Tai Chi training, even though it was subtle. Repetitive weight-shifting to the paralysed side had a significant effect on the asymmetrical posture of stroke survivors. The authors conclude that combining Tai Chi with general physiotherapy was more effective for improving static balance of stroke survivors.

Most studies and reviews retrieved from the databases found that balance improved in the Tai Chi groups compared to the controls within the populations investigated (Burschka et al., 2014; Hackney & Earhart, 2008; Hain, Fuller, Weil & Kotsias, 1999; Hakim et al., 2010;

Kim et al., 2015). However, Wu et al. (2018) conducted a meta-analysis and found that despite an improvement in balance among the Tai Chi group using the BBS, there was unexplained statistical heterogeneity observed, which may be related to differences among studies in the study population, different types of Tai Chi, intensity and duration. Therefore, the authors advised caution when accepting the results. Results in the meta-analysis by Wu et al. (2018) reached high heterogeneity and low reliability. The authors acknowledged that this low quality of evidence was due to lack of information on random sequence generation, allocation concealment and the blinding of outcome assessors.

Limitations

Only short-term effects of Tai Chi on balance were evaluated by Wu et al. (2018). The authors recommend long-term effects to be assessed, particularly after long-term use of medication. Maciaszek and Osiński (2010) and Yang, Li, Gong, Zhu & Hao (2014) agree that the follow-up effects of Tai Chi should be done on those with Parkinson’s disease.

Chen et al. (2015) recognise that according to the Cochrane Collaboration

recommendations, all studies included in their review were of low quality with a high bias risk. Out of the three studies they reviewed which implemented Tai Chi, only one was clear about the style of Tai Chi used (Yang). Jiménez-Martinez al. (2013) acknowledge the difficulty in performing a meta-analysis due to the different Tai Chi styles, outcome

measures and sample sizes. Subgroup analyses are recommended by Maciaszek and Osiński (2010) to determine the effectiveness of interventions in people with different

characteristics.

Improvements in balance may not directly relate to a reduction in falls. Therefore, a direct measure of the number of falls should be included (Maciaszek and Osiński, 2010).

Hain et al. (1999) suggest that Tai Chi may be useful for balance rehabilitation but stated an appreciable risk of falls may be present, especially in a class of ten participants, if close supervision is not given.