In this study, the block randomization method was used through the website www.randomization.com. For this purpose, each subject was first assigned a number as a unique identification code and an 18-digit sequence (equal to the sample size) was created. Then, the names of the intervention groups were defined in the relevant section of the website, including: Experimental Group 1, first brain stimulation and then MVF (tDCS offlin-pre), Experimental Group 2, first MVF and then brain stimulation (tDCS-offlin-post), and the control group (sham stimulation group with MVF). After defining the groups and in order to prevent potential problems caused by blocking with fixed-size blocks, the method of randomly selecting blocks of different sizes was used for blocking. In this case, since the sample size was known, the block sizes were unequal and a multiple of the number of intervention groups (for example, blocks of 2, 4, 6, or 8). The website has the ability to randomly create sequences of blocks of different sizes. In the final step, by executing the Plan Generate command on the website, all subjects were randomly assigned to blocks of different sizes that themselves had a random sequence. Finally, by using the number (code) assigned to each subject and examining the blocks, the group of each subject was determined.
In this double-blind study, the researcher and participants will be blinded to the type of transcranial electrical stimulation used in each session. In the present study, the Neurostim stimulator will be used to induce direct current electrical stimulation. For this purpose, a person outside the research team will be responsible for applying electrical stimulation in the experimental sessions. In order to blind the participants, after they sit on a special chair, the brain electrical stimulation device is hidden from their sight and is completely covered by a cover, and the electrodes will be placed on the desired areas by the test taker. In order to blind the researcher, the researcher also leaves the laboratory before applying the intervention and returns to the testing site after the stimulation period has elapsed, the electrodes are removed, and the stimulator is turned off. Also, in the sham stimulation mode, according to standard protocols, an active current is induced on the head for 30 seconds to induce a sensation similar to the active stimulation mode, and then the current is interrupted and the stimulation is deactivated.