Effects of Percutaneous Electrical Stimulation in Patients With Chronic Supraspinatus Tendinopathy

Pain Intensity

The Numerical Pain Rating Scale (NPRS) will be used to estimate pain intensity. This scale assigns a number between 0 (no pain) and 10 (worst possible pain) (Farrar et al., 2001). Using this instrument, the patient will rate the intensity of the pain they feel at the worst time of day and the average level of pain experienced over the past week. This easy-to-complete, quick, and simple scale has shown a Minimal Detectable Change (MDC) of 1.3 to 2.8 points in patients with musculoskeletal problems and 1.7 points in subacromial pain syndrome.

Pressure Pain Threshold (PPT)

The test will be performed using a mechanical pressure algometer at specific study points to determine the amount of pressure applied at which the sensation of pressure changes to pain. The patient will be seated in a comfortable and relaxed position. The procedure consists of applying the tip of the algometer perpendicular to the skin and maintaining a pressure that will be progressively increased until the pain threshold is reached. Subjects will be instructed to signal when this pressure pain threshold (PPT) is exceeded. The physiotherapist will take three measurements, with a 30-second rest period between each measurement, calculating the average value in kg.. Measurements will be taken on the affected side, in the subacromial space region (treatment area), in the upper trapezius muscle (midpoint between the neck and shoulder muscle fibers), in the ventral part of the middle head of the deltoid muscle (segmental area), and in the tibialis anterior muscle,

Function

The Constat-Murley (CM) questionnaire is a commonly used, specific instrument for assessing overall shoulder joint function (Roy et al., 2010). The maximum score is 100 points, with 90 to 100 considered excellent, 80 to 89 good, 70 to 79 fair, and below 70 poor, although scores may vary with age. This tool includes a subjective assessment of the patient's pain and ability to perform daily activities (35 points), and an objective assessment of mobility and strength through physical examination (65 points). Its use has been specifically validated in shoulder arthroplasty, rotator cuff repair, adhesive capsulitis, and proximal humerus fractures. This tool has shown a Minimal Detectable Change (MDC) of 11.6 points in patients with subacromial impingement.

Disability

The Shoulder Pain and Disability Index (SPADI) focuses on the degree of pain or disability caused by shoulder problems during the past week. It is a self-administered questionnaire consisting of two dimensions: one for pain and one for functional activities. The pain dimension comprises five questions about the severity of pain. Functional activities are assessed with eight questions, designed to measure the degree of difficulty a person has performing various activities of daily living that require the use of the upper extremities. The patient answers the questions using a visual analog scale (from 0 to 10), both in the pain dimension (0 equals no pain and 10 equals the worst pain imaginable) and in the disability dimension (0 equals no difficulty and 10 equals so difficult that help was required). In patients with subacromial pain syndrome, this questionnaire has shown a Minimal Detectable Change (MDC) of 20.5 points.

Overall Perception of Clinical Change

The overall change rating will be obtained using an 11-point scale, used to estimate the clinical change perceived by the patient. Participants will be asked to rate the overall perceived change in their shoulder pain condition, from the start of the study to the present, based on three possible options: worse, no change, or better. If participants indicate worse, they will be asked how much worse on a 5-point scale (from much worse to slightly worse). Similarly, if participants indicate better, they will be asked how much better on a 5-point scale (from slightly better to much better). The minimum clinically significant change is 2 points.

Kinesiophobia

The Tampa Scale for Kinesiophobia (TSK-11) is a widely used instrument to assess fear of movement or re-injury. The abbreviated version is the most common in current clinical practice and consists of 11 items, to which the patient responds on a 4-point Likert scale, indicating their level of agreement with the statements. The range is from 11 to 44 points (minimal: ≤ 22 points; low: 23-28 points; moderate: 29-35 points; and high: ≥ 36 points). The resulting instrument demonstrates good reliability (internal consistency and stability) and validity (convergent and predictive), with the advantage of its brevity. A high score indicates extreme fear of movement, while a low score indicates insignificant fear of movement. This scale has been used in various clinical contexts, especially to assess fear of movement in patients with chronic musculoskeletal pain, including shoulder pain.

Perceived self-efficacy with pain

A 10-item Pain Self-Efficacy Questionnaire will be used to assess patients' confidence in performing daily activities while experiencing pain, in this case, shoulder pain. The Pain Self-Efficacy Questionnaire (PSEQ-10) is a reliable and valid tool for the point assessment of self-efficacy in people with chronic shoulder pain (Medina et al., 2025). Findings suggest a moderate association between pain self-efficacy, chronic shoulder pain, and disability. This variable is considered to modulate the results after treatment, and even has implications for patients' functioning in their daily lives.

Adherence to the exercise program

Adherence to the prescribed exercise program will be assessed using, on the one hand, an exercise diary documenting the completion of scheduled sessions and, on the other hand, the Exercise Adherence Rating Scale (EARS). This is a 6-item instrument designed for this purpose. The items are scored using an ordinal response scale (from 0 = strongly agree to 4 = strongly disagree). The six items are summed, and items with positive statements (items 1, 4, and 6) are scored in reverse. Higher scores indicate greater adherence (0 to 24). The scale would be completed at the end of the intervention (12 weeks) and at the end of the follow-up period. The exercise session diary will allow for the calculation of the percentage of training sessions completed by the subject in each intervention group. Regarding the total number of sessions between T0 and T3 (36 sessions - 3 sessions per week, for 12 weeks). A minimum of 12 completed sessions, equivalent to 4 weeks of in