The purpose of this study is to investigate the effects of applying Transcranial direct current stimulation on pain levels and function, quality of life, muscle strength and range of motion in individuals with subacromial pain syndrome.

This is a controlled, randomized and blind clinical trial, which will be carried out with individuals from the city of Natal/RN, aged between 18 and 65 years, of both sexes, diagnosed with subacromial pain syndrome, who present a level of pain greater than 3 on the Numerical Pain Scale, at rest, for at least 3 months. The research sample will be non-probabilistic, in which they will be randomly distributed into two distinct groups: active tDCS (active stimulation) and sham tDCS (stimulation turned off after 20 seconds). This research was submitted to the UFRN Research Ethics Committee through the national interface Plataforma Brasil. This research covers the ethical aspects guided by Resolution 466/2012 of the National Health Council and the Declaration of Helsinki for research with human beings. In addition, the research will be registered in Clinical Trials. All data will be recorded in the laboratory's database under confidentiality and may only be processed by the responsible researchers. The study will only begin after the issuance of the reference opinion approving the project. All subjects will be duly informed and guided regarding the scheduled procedures, which will only be carried out after reading, accepting and signing the Informed Consent Form. After approval by the Research Ethics Committee, following resolution 466/2012, a pilot study was carried out to adapt all research procedures, as well as training the researchers involved. Volunteers will be duly informed about the objectives and advantages of their participation in the study, and will then undergo an assessment of pain sensation, using the Numerical Pain Scale; assessment of shoulder range of motion, using the Smartphone clinometer application; assessment of muscle strength through flexion, hyperextension, medial and lateral rotation movements of the shoulder, using a portable dynamometer; will complete the Douleur Neuropathique 4 questionnaire (DN4) to screen for neuropathic pain, the Disabilities of the arm, shoulder and hand questionnaire (DASH) to assess upper limb function, and the Short Form 36 Health Survey questionnaire (SF-36) to assess health-related quality of life. They will then undergo 20 minutes of stimulation for 5 consecutive days, according to the pre-determined group. The assessments will be repeated at the end of the intervention and in a 1-week follow-up, in which they will receive an educational booklet.

Inclusion Criteria:

• Unilateral pain in one shoulder
• Pain level ≥ 3 on the Numerical Pain Scale (END), at rest, for at least 3 months
• No previous treatment with tDCS
• Present graded disability on the DASH questionnaire (> 15 points)
• At least three positive tests, among the five indicated below: Neer, Hawkins, Jobe, Patte or painful abduction arch.

Exclusion Criteria:

• Indication for surgical repair and/or history of shoulder surgery
• Shoulder fracture and/or dislocation
• Partial or total rupture of one of the rotator cuff tendons and/or the long head of the biceps
• Fibromyalgia
• History of epilepsy
• Panic syndrome
• Implantable devices in the skull
• Significant neurological or psychiatric diseases
• Severe cardiopulmonary, renal and hepatic diseases
• Current pregnancy.