Vimolratana O.Lackmy-Vallee A.Aneksan B.Hiengkaew V.Klomjai W.Mahidol University2023-05-152023-05-152023-12-01BMC Sports Science, Medicine and Rehabilitation Vol.15 No.1 (2023)https://repository.li.mahidol.ac.th/handle/20.500.14594/81337Background: Transcranial direct current stimulation (tDCS) is a technique that modulates brain excitability in humans. Increasing the stimulation intensity or duration within certain limits could enhance tDCS efficacy with a polarity-dependent effect; anodal stimulation increases cortical excitability, whereas cathodal stimulation decreases excitability. However, recent studies have reported a non-linear effect of cathodal tDCS on neuronal excitability in humans, and there is no conclusive result regarding the effect of cathodal tDCS on muscle performance. Methods: Our study aimed to investigate the immediate effects of different intensities (i.e., 1, 1.5, and 2 mA and sham tDCS) of cathodal tDCS on muscle strength in healthy participants. All participants [mean age 23.17 (3.90) years] were recruited and randomly allocated into four groups (1, 1.5, and 2 mA cathodal tDCS and sham tDCS). Muscle strength in bilateral upper and lower extremities was measured before and immediately after tDCS using a handheld dynamometer. Results: Our results showed that cathodal tDCS at 1 and 1.5 mA reduced muscle strength bilaterally in upper and lower extremity muscles, whereas stimulation at 2 mA tended to increase muscle strength on the dominant limb. Conclusion: These findings support the non-linear effects of cathodal tDCS on muscle strength, which should be considered for the clinical use of tDCS in motor rehabilitation. Trial registration: NCT04672122, date of first registration 17/12/2020.Health ProfessionsArticleSCOPUS10.1186/s13102-023-00621-72-s2.0-8514699587920521847