Randomization and masking
MCI
The random grouping sequence of the participants in this study was generated by dedicated statistical staff using Statistical Package for the Social Sciences (SPSS) Statistics 20.0 (IBM, Chicago, IL, USA). Random grouping sequences were stored in a light-impermeable sealed envelope. A total of 180 eligible participants with MCI were randomly assigned into the Tai Chi combined with tDCS group (TCT), Tai Chi combined with sham tDCS group (TCS), walking combined with tDCS (WAT), and walking combined with sham tDCS group (WAS) in order of inclusion. Although blinding is not possible for participants in exercise intervention research, the staff collecting the outcomes and data analysts will have no knowledge of the group assignment. Blinding was performed after the statistical analysis of the study was completed.