Clinical research question: Is more effective therapeutic exercise combined with high definition transcranial direct current stimulation (HD-tDCS) than therapeutic exercise combined with sham HD-tDCS in athletic adult patients with chronic ankle instability (CAI)? Objectives: To analyse the effectivity of high definition transcranial direct current stimulation (HD-tDCS) combined with therapeutic exercise in athletic adult patients with chronic ankle instability, compared to therapeutic exercise and sham HD-tDCS. Methodology: Research design: A prospective, double-blind, randomized controlled trial (RCT) is designed in athletic adults with CAI. Sample: The sample will be formed by athletic adults diagnosed with CAI following the selection criteria of the International Ankle Consortium. Randomization: Subjects will be divided into two groups by means of balanced randomization performed with free software, simple randomization will be performed. Also, the patients and physiotherapist will be blinded and do not know in which group are. Intervention: There will be two groups, the experimental group treated with therapeutic exercise and real HD-tDCS and the control group treated with therapeutic exercise and sham HD-tDCS. The intervention is for 8 weeks and afterwards the patients will be followed during 8 weeks more. The treatment is divided in 3 stages in which the patients will overtake in proportion with their progression. Measures: There will be 7 assessment for the study patients. One before the rehabilitation start, two between intervention, another when the rehabilitation is finished and three more at 2,4 and 8 weeks respectively from the rehabilitation finish. The variables that are assessed are pain (NRS scale), motor control (Jump test), Health related quality of life (DPA scale) and ROM (My ROM app).