Does Cathodal Preconditioning Enhance the Effects of Subsequent Anodal Transcranial Direct Current Stimulation on Corticospinal Excitability and Grip Strength?

Abstract: Lewis, A, Rattray, B, and Flood, A. Does cathodal preconditioning enhance the effects of subsequent anodal transcranial direct current stimulation on corticospinal excitability and grip strength? J Strength Cond Res XX(X): 000-000, 2024-Inconsistent effects of transcranial direct current stimulation (tDCS) on corticospinal excitability (CSE) and exercise performance are commonly reported. Cathodal preconditioning, involving cathodal tDCS delivered before anodal tDCS over the same region, may enhance changes in CSE and exercise beyond that resulting from anodal tDCS alone. This study aimed to investigate whether the effects of anodal tDCS on CSE and isometric grip strength can be enhanced by cathodal preconditioning. Thirty-five healthy subjects aged 19-37 years completed a familiarization session followed by 4 stimulation conditions presented in a randomized cross-over design across 4 separate sessions. tDCS doses were applied at 2 mA over the primary motor cortex for 10 minutes. Corticospinal excitability was assessed using 120% of resting motor threshold and an input/output curve of motor evoked potentials of the first dorsal interosseous. Grip strength was evaluated as time to exhaustion (TTE) in a sustained isometric contraction. Relative to conventional sham stimulation, TTE was significantly increased by 15% after conventional anodal tDCS. Corticospinal excitability increased in response to tDCS, but this effect did not differ across conditions. Cathodal preconditioning before anodal stimulation did not increase CSE or grip strength beyond that seen in the other stimulation conditions. Our findings did not reveal any significant impact of stimulation type on CSE. Notably, anodal tDCS led to a significant improvement in grip strength endurance. However, cathodal preconditioning did not seem to increase the effect of subsequent anodal stimulation on CSE nor grip strength.