The authors stated that the drawbacks of this present study were: First, its small sample size and insufficient statistical power. Second, the stimulation parameters and duration of the studies were not consistent, which made these investigators doubted whether meta-analysis could be performed. However, the results based on RCTs were excellent despite inconsistent variables. Third, when analyzing the data of Pad test, a hug heterogeneity that most likely caused by incomplete experimental design was recorded if these researchers added the study by Manganotti et al (2007) to the analysis. Therefore, this study data were finally excluded by performing sensitivity analysis. These researchers stated that further well-designed RCTs with a long-term follow-up with a large sample size are needed.