Introduction: Transcranial direct current stimulation (tDCS) is a non-invasive technique used to modify the activity of the cortex of the brain. This form of current is capable of inducing changes in the electrical activity inside and outside of the neurons, which leads to a change in the resting membrane potential and thus improves the efficiency of the neural synapse. Therefore, the aim of this study was to investigate the effect of tDCS over motor cortex on strength and endurance performance of healthy collegiate subjects.
 
Materials & Methods: In total, 10 young and healthy male subjects (age range: 21.23±1.41 year) voluntarily participated in this study. One-repetition maximum (1 RM) of knee extension and anthropometric measurements were determined on the first session. In the next session, the subjects performed 4 sets with 90% of 1 RM to exhaustion for right knee extensors on the leg extension. In the other session, 3 sets with 70% of 1 RM to exhaustion for the right elbow flexors was performed with an interval of 72 h on the preacher curl machine. The rest time between the turns in the activity of the knee-lowering muscles and elbow flexing of the elbows was 3 min and 90 sec, respectively. Meanwhile, the electrical activity of the involved muscles and the number of repetitions performed in each set were recorded in this study. Immediately after performing all sets, anodal stimulation (2 mA for 15 min) and sham (2 mA for 15 min, which was interrupted after 30 sec) were used in two sessions in a randomized cross-over design over cranium of the subjects. The electrodes (anode and reference) were connected to a constant current excitation device with a maximum of 10 mA. Immediately after applying tDCS, the subjects again performed the initial tests, and the electrical activity of the involved muscles and the number of repetitions were re-recorded in each set. The electromyography signal amplitude data were collected using a 2000 Hz electromyography device. Data were analyzed using ANCOVA. P-value less than 0.05 were regarded statistically significant. Ethics code: IR.LUMS.REC.1396.303
 
Findings:  The results showed a significant difference within the two stimulation methods regarding the number of repetitions and the volume of work performed in the strength training session (P=0.001). However, there was no significant difference within the two stimulation methods in terms of the number of repetitions and the volume of work performed in the endurance training session (P>0.05). Moreover, no significant difference was observed within the two stimulation methods regarding the electrical activity of rectus femoris (P=0.197), vastus lateralis (P=0.363), vastus medialis (P=0.227), and biceps brachialis (P=0.078) muscles before and after the treatment.
 
Discussion & conclusions: The results of this study indicate that an anodal tDCS stimulation session leads to an increase in the strength of the knee extensor muscles. However, it has no effect on the endurance performance of elbow flexors which may result from the electrode montage in this study. Moreover, an anodal tDCS stimulation session has no significant effect on the muscular electrical activity during performing strength and endurance activities.