Study design: Systematic review and meta-analysis.
Objectives: To summarize the available evidence regarding the effects of trans-spinal direct current stimulation (tsDCS) on spinal monosynaptic circuit excitability in healthy individuals.
Setting: Applied Neuroscience Laboratory, Brazil.
Methods: Abstract screening was performed independently by two authors for studies found in the following databases: PubMed, CINAHL, PsycINFO, Web of Science, and LILACS. If the authors were unable to agree, a third reviewer was consulted. Randomized clinical trials that reported monosynaptic reflex measures were included. Methodological quality was assessed using the Cochrane tool for assessing the risk of bias, and information extracted about the spinal neurophysiological and stimulation protocols and their results.
Results: The initial search identified 538 studies. After applying the inclusion criteria and excluding duplicates, seven crossover studies were included in the risk of bias assessment, and six studies in the meta-analyses. The meta-analysis results did not show any significant differences between anodal (pooled standardized mean difference (SMD) = -0.09, 95% CI = -0.72 to 0.55, p = 0.79, I2 = 67%) or cathodal tsDCS (pooled SMD = 0.28, 95% CI = -0.07 to 0.63, p = 0.11, I2 = 0%) and sham tsDCS for Hoffmann reflex modulation.
Conclusion: tsDCS did not affect the Hoffmann reflex, as shown in six studies. However, these findings come from studies with selection, performance and detection bias, and further research is needed to examine the effect of this intervention.