The objective of this clinical trial is to evaluate the effects of transcranial direct current stimulation (tDCS) combined with constraint-induced therapy (CIT) on upper limb motor recovery in individuals after stroke.

The main questions it aims to answer are:

Does the combination of tDCS and CIT improve upper limb motor function compared to CIT alone?

Does the combined intervention promote changes in muscle morphology and electromyographic activity?

Researchers will compare the group receiving tDCS combined with constraint-induced therapy to the group receiving constraint-induced therapy alone to determine whether the addition of cortical neuromodulation enhances motor recovery outcomes.

This is a randomized, controlled, and blinded clinical trial in which participants will be divided into two groups: one group will receive tDCS combined with CIMT, and the other will undergo only CIMT. The protocol will include 18 sessions over six weeks, three times a week.

Clinical and instrumental assessments will be performed before, during, and after the intervention, including the Fugl-Meyer scale for the upper limb, musculoskeletal ultrasound for morphological analysis, and surface electromyography for muscle activity assessment.

The target population will include individuals aged between 40 and 80 years, of both sexes, diagnosed with stroke as defined by the International Classification of Diseases (ICD-10) with mild to moderate impairment in the upper limb according to the Fugl-Meyer Assessment - Upper Extremity (FMA-UE) scale, who present alterations in the muscle function of the affected upper limb.

A convenience sample will be used, with an estimated inclusion of 40 (forty) individuals who meet the inclusion and exclusion criteria.

In this study, individuals will be included who: (1) have a clinical diagnosis of stroke confirmed by imaging examination and/or a report issued by a neurologist; (2) are in the chronic phase of the lesion with an occurrence time greater than six months; (3) hemiparesis with brachial predominance, mild to moderate motor deficit in the affected upper limb defined by a score between 19 and 55 points on the FMA-UE; (4) possess minimum joint integrity to perform the movements required in the protocol with an active range of motion of at least 20° of wrist extension, 10° of extension of the metacarpophalangeal and interphalangeal joints and 20° of elbow extension considering the standard position of 90° elbow flexion, measured with a Carci® goniometer; (5) demonstrate the ability to understand and follow simple commands in the Mini Mental State Examination (MMSE) (ANNEX II) with a score higher than 23 points for literate individuals and lower than 15 points for illiterate individuals. Individuals with the following will be excluded from the study: (1) diagnosis of epilepsy; (2) intracranial metallic implants or implantable electronic devices; (3) contraindications to transcranial direct current stimulation (tDCS), including skin lesions on the scalp; (4) severe musculoskeletal limitations that prevent the execution of tasks; (5) history of recurrent stroke; (6) associated musculoskeletal and neurological pathologies of a disabling nature; (7) use of botulinum toxin in the previous three months; (8) uncontrolled systemic arterial hypertension or diabetes mellitus; (9) clinically relevant heart disease; (10) apraxia and aphasia of comprehension; (11) fracture and pain during movement or displacement of the affected limb, or pain related to shoulder subluxation. Those who feel uncomfortable, withdraw from the research, do not respect the rules established in the Informed Consent Form, or do not attend the stages of the study will also be excluded.

STAGE 1: Patients will be recruited through UEAFTO and contacted by the responsible researcher. Initially, the objectives and procedures of the research will be briefly explained and, after the participant's agreement, the evaluation will be scheduled.

STAGE 2: Subsequently, the evaluation form constructed by the student will be applied to rule out exclusion criteria and the FMA-UE and MMSE scales will be applied. After this stage, volunteers who are eligible and in accordance with the study's inclusion criteria and who are interested in participating will sign the Informed Consent Form (APPENDIX C), referring to voluntary participation, where the researchers will explain and deliver in duplicate the document reporting how the research will take place and its objectives. It is worth noting that the Informed Consent Form will be signed on all pages by the volunteers.

The measurement of all assessment instruments will be carried out at three times: (1) in the pre-treatment period, on the first day, before the start of the interventions; (2) during the treatment, in the 9th session; and (3) in the post-treatment period, 15 days after the end of the 18 sessions, corresponding to the follow-up period.

STAGE 3: After signing the Informed Consent Form, the participant will be prepared for the evaluation of muscle trophism with kinesiological ultrasound of the biceps brachii muscle on both sides.

Structural and functional data of the upper limbs will be collected by kinesiological ultrasound, using the Saevo EVUS 8 ultrasound device, with a linear transducer. All measurements will be obtained with the participant in the supine position, ensuring complete muscle relaxation.

The muscle thickness and pennation angle of the brachialis and biceps brachii muscles will be measured in B-mode, as described by Valla et al. (2017). For standardization of the evaluation site, the arm length will be measured from the lateral border of the acromion to the lateral epicondyle of the humerus and divided into three equal parts, with the middle third being used for image acquisition and measurement of variables.

The muscle distance and the ratio between subcutaneous tissue and muscle tissue of the brachialis and biceps brachii muscles will be obtained with the transducer positioned transversely to the arm, with the probe mark oriented medially. The pennation angle assessment will be performed with the transducer positioned perpendicularly, with the probe mark oriented superiorly. As an anatomical reference for measuring the pennation angle, the biceps brachii muscle will preferably be used, due to the greater ease of access and ultrasonographic identification, without prejudice to the complementary analysis of the brachialis muscle. All measurements will be performed bilaterally (right and left side) due to greater feasibility and reproducibility (Kim, et al 2021).

Additionally, the muscle amplitude of the biceps brachii muscles will be analyzed in the contraction and relaxation states using M-mode, with the probe mark positioned medially.

The transducer location will be marked with a dermatographic pencil, with the aim of increasing the consistency of the measurements, considering that muscle thickness presents heterogeneity along its surface. For each variable, three consecutive and independent measurements will be taken, and the average of the values obtained will be used to minimize the variability of the measurements.

A generous amount of ultrasound gel will be applied to ensure ideal coupling of the ultrasound beam, avoiding deformation of the soft tissues caused by the pressure of the transducer during the examination. To obtain standardized and uniform images, the transducer will be positioned perpendicular to the skin and possibly slightly angled (in the elevational direction) in order to obtain the brightest echo of the muscle fascia.

4th STAGE: Following the aforementioned stage, an evaluation will be performed using electromyography (EMG) of the target muscles, biceps brachii, wrist flexors and extensors, bilaterally, with the aim of measuring electrical activity and maximum contraction force.

Electromyographic signal collection will be performed using surface electromyography (EMGs), utilizing the Miotool 400® electromyograph (Miograph 2.0 USB®), with a four-channel module, 14-bit resolution, and a sampling frequency of 2000 Hz per channel. The signals will be captured by differential surface sensors (SDS 500), with circular Ag/AgCl electrodes (10 mm in diameter), positioned in pairs with an interelectrode distance of 2 cm (Rocha, 2017). For standardization and reduction of skin impedance, trichotomy, asepsis with 70% alcohol, and local exfoliation will be performed before electrode placement. The motor points of the muscles of interest will be previously located using a portable electrical stimulator, according to SENIAM recommendations. The reference electrode will be placed over the tuberosity of the medial malleolus (Hermens, 2000).

Data collection will be performed in a controlled environment, with a well-lit room, an approximate temperature of 23°C, and without interference from electronic devices. Initially, the participant will be positioned in a seated position (90° of hip, knee, and ankle flexion), with the trunk stabilized and upper limbs supported on a fixed surface, to record the activity of the biceps brachii, wrist flexors, and extensors.

To obtain the maximum voluntary contraction (MVC), the participant will perform three sustained contractions for 15 seconds, with a one-minute interval between them, upon the standardized verbal command "force" and "hold." The raw signals (RAW), the RMS (root mean square), and the maximum force will be recorded by the Miograph® system, with a 10-second interval selected for analysis, starting two to three seconds after the beginning of the contraction. For each muscle and side evaluated, the average of the three MVCs will be used for the final analysis (Santos et al, 2016).

STAGE 5: After the initial assessment, volunteers will be randomized and distributed into two groups: anodal electrical stimulation and containment therapy (α-tDCS + CIMT) and CIMT alone. Randomization will be performed using the block method, with the aim of ensuring a similar number of participants in each group. This process will be conducted by an independent and blinded researcher, using a computerized random sequence generator (https://www.randomizer.at/), which will allocate participants to one of the two study groups (α-tDCS + CIMT or CIMT).

To ensure concealment of the allocation, opaque and sealed envelopes will be used, which will only be opened at the time of the intervention. The group allocation will not be revealed until the data analysis is complete.

In this study, the researcher responsible for randomization, the evaluator, and the statistician will be blinded. Only the therapist responsible for applying the interventions will have knowledge of the distribution of participants among the groups, adopting all necessary measures to ensure the blinding of the other participants until the end of the study.

The research data will be stored in coded spreadsheets, without identification of the groups, for later statistical analysis. All documents related to the study will be duly archived for a minimum period of five years, in accordance with current regulations.

STAGE 6: After randomization of participants, treatment will begin using the protocol previously established by the researcher, consisting of 18 supervised sessions over six weeks, with a frequency of three times per week and a duration of 50 minutes per session.

For tDCS application, the Microestim tDCS model stimulator (NKL Electronic Products Ltd., Brazil) will be used, with a pair of 5 cm x 7 cm (35 cm2) sponge electrodes, which will be soaked in saline solution providing a current density of 0.04 mA/cm2 that will be within safety limits (Russo et al 2017).

Regarding electrode placement, the anodic electrode will be fixed over the primary motor cortex (M1) of the affected hemisphere, corresponding to point C3 or C4, according to the international 10-20 electroencephalography system. The cathodic electrode will be positioned over the primary motor cortex of the unaffected hemisphere, at point C4 or C3, respectively, according to the same system. This choice was based on a study by Sun Ho et al (2021) that studied the effects of tDCS and ICT to improve upper limb function after stroke.

Volunteers in the a-ETCC group will undergo anodal stimulation in M1 with constant direct current at an intensity of 2 mA, for 20 minutes per session. Recent studies have demonstrated the efficacy and safety of these parameters when applied to adult post-stroke patients along with CIMT (Schlaug et al 2025, Garrido et al 2023, Kim et al. 2021).

At the time of CIMT application, a sling will be used positioned on the healthy upper limb (UL), then the affected or paretic UL will be stimulated to perform tasks involving activities of daily living and/or everyday life, with the volunteers seated, ergonomically and with the material used for the activities positioned on a table. The healthy UL will be restrained by the sling, while the paretic UL will perform the activities.

The CIMT protocol will involve three main components: repetitive task-oriented training of the affected upper limb; the transfer package, developed to facilitate the generalization of therapeutic gains obtained in the clinical setting to the participant's daily activities; and the restriction of the unaffected upper limb, with the aim of inducing functional use of the affected limb, as described in the classic study by Taub et al. (2006).

It is worth noting that the restraint of the unaffected limb will occur exclusively during the intervention period, corresponding to the total time of each session. The activities will be organized into different categories, according to the therapeutic objectives:

• Ringing the bell: This consists of alternately pressing five bells positioned on the table, using the affected upper limb, with the fingers extended and the palm of the hand in contact with the devices. The patient's position remains fixed during the execution of the task, while the therapist adjusts the location of the bells according to the participant's functional level.
• Placing rubber balls in the basket: The participant must hold, with their affected hand, rubber balls with a diameter of less than 7 cm and transfer them to a basket with an approximate diameter of 15 cm. The patient's position is kept fixed, and the difficulty level of the task is adjusted by the therapist by modifying the distance, position, and height of the basket.
• Placing pegboard pegs in the basket: From a seated position, the participant must move cylindrical pegs, approximately 2 cm in diameter and 8 cm long. height, from left to right or vice versa, using the affected upper limb. The therapist adjusts the height and position of the target basket according to the patient's functional level.
• Turning cards: Several cards positioned on the table are turned one by one with the affected hand, stimulating grasping, pronation and supination movements of the forearm, as well as fine motor coordination.
• Reaching for a pitcher and pouring water: The participant must reach for a pitcher with an approximate capacity of 500 ml, hold it with the affected hand and pour water into five glasses positioned on the table, training reach, grasping, postural control and bimanual coordination when necessary.
• Bringing the glass to the mouth: Consists of picking up a glass with the affected hand and bringing it to the mouth, simulating the functional action of drinking liquids.
• Bringing a spoon to the mouth: The participant must hold a spoon with the affected hand and perform the movement of bringing the utensil to the mouth, reproducing the functional activity of eating.
• Combing hair: The task involves holding a comb or brush and performing functional movements of combing hair, stimulating range of motion, coordination, and motor control of the affected upper limb.
• Cleaning the table with a sponge: This consists of performing circular and directional movements on the table surface using a sponge, promoting training in reach, strength, coordination, and motor control.
• Fitting games: Activities that involve fitting pieces of different shapes and sizes together, stimulating manual dexterity, fine motor coordination, motor planning, and visuomotor control.

These exercises were based on the protocols described by (Garrido et al. 2023, Saygili et al 2024, Kim et al. 2021 and Terranova et al. 2021), with adaptations made by the author. Each task will be performed for 5 minutes, totaling 50 minutes of therapy per session. The degree of difficulty of the tasks will be progressively increased from the 9th session onwards, by modifying the distance, size, weight and material of the objects used.

Before the start of each session and immediately after its completion, the vital signs of all volunteers will be measured, with the aim of monitoring the safety and tolerability of the interventions.

Inclusion Criteria:

• (1) present a clinical diagnosis of stroke confirmed by imaging examination and/or report issued by a neurologist; (2) are in the chronic phase of the lesion with an occurrence time greater than six months; (3) hemiparesis with brachial predominance, mild to moderate motor deficit in the affected upper limb defined by a score between 19 and 55 points on the FMA-UE; (4) have minimum joint integrity to perform the movements required in the protocol with an active range of motion of at least 20° of wrist extension, 10° of extension of the metacarpophalangeal and interphalangeal joints and 20° of elbow extension considering the standard position of 90° elbow flexion, measured with a Carci® goniometer; (5) demonstrate the ability to understand and follow simple commands on the Mini Mental State Examination (MMSE) (ANNEX II) with a score higher than 23 points for literate persons and lower than 15 points for illiterate persons.

Exclusion Criteria:(1) diagnosis of epilepsy; (2) intracranial metallic implants or implantable electronic devices; (3) contraindications to transcranial direct current stimulation (tDCS), including skin lesions on the scalp; (4) severe musculoskeletal limitations that prevent the execution of tasks; (5) history of recurrent stroke; (6) associated disabling musculoskeletal and neurological pathologies; (7) use of botulinum toxin in the previous three months; (8) uncontrolled systemic arterial hypertension or diabetes mellitus; (9) clinically relevant heart disease; (10) apraxia and aphasia of comprehension; (11) fracture and pain during movement or displacement of the affected limb, or pain related to shoulder subluxation. Those who feel uncomfortable, drop out of the research, do not respect the rules established in the Informed Consent Form (APPENDIX C), or do not attend the stages of the study will also be excluded.