Transcranial Direct Current Stimulation (tDCS) is a non-invasive neuromodulation technique used in this study to enhance the central analgesic effects of the combined Active Pain Coping treatment. The intervention involves the delivery of a low-intensity electrical current through the scalp to modulate cortical excitability. The Anode is positioned over the Primary Motor Cortex (M1) (C3) and the Cathode is placed over the Orbitofrontal region (FP2). The Active Group receives a constant 2 mA current for 20 minutes to modulate brain activity.

Therapeutic Exercise (TE) is the most extensive component of the multimodal program, administered in structured group sessions lasting approximately one hour. The protocol is designed to be adapted to each patient's physical condition, and includes a graded exposure component to ensure safety and mitigate pain flares. Each session includes a warm-up (mobility/activation); a main phase focused on conscious movement, coordination, balance, agility, and muscular strength; and a final cool-down that incorporates flexibility, relaxation, and mindfulness. The primary purpose of this structured exercise is to safely promote physical activity, reverse physical deconditioning and muscle atrophy, reduce fear of movement (kinesiophobia), and reinforce the new neuroscientific understanding of pain acquired, thereby sustaining the overall analgesic effects of the treatment.

Control Group receives an identical-looking Sham (Placebo) stimulation, where the device runs for only the initial minute (at 2 mA) before turning off silently, ensuring the participants remain blinded to the treatment they receive.

Pressure Pain Thresholds (PPTs) are measured using a Wagner brand Fisher digital algometer to quantify local pain sensitivity in $\text{kg/cm}^2$. Measurements are taken at four specific anatomical reference points bilaterally: the midpoint between the posterior border of the acromion and the C7 spinal process, and the midpoint between the highest part of the superior border of the iliac crest and the spinal process at the same height. At each point, two consecutive measurements are taken by increasing pressure at a rate of $1\text{ kg/cm}^2$ per second. The threshold is determined when the participant reports that the sensation of pressure turns into pain. The final PPT score for each site is the average of the two consecutive measurements. A lower PPT indicates increased local pain sensitivity.

Temporal Summation (TS) is used to assess central sensitization (the wind-up phenomenon). It is provoked by applying 10 consecutive pulses using a pressure algometer at the previously determined Pressure Pain Threshold (PPT) for the specific location. For each pulse, pressure is gradually increased at a rate of 2kg/s to reach the PPT, held for 1 second, and then released with a 1-second interval before the next pulse. The participant rates the pain intensity of the first, fifth, and tenth pulse on a Numerical Rating Scale (NRS) from 0 (no pain) to 10 (worst possible pain). A score increase between the first and tenth pulse indicates efficient temporal summation (central sensitization).

The Pain Catastrophizing Scale (PCS) is a 13-item psychometric tool used to assess negative cognitive and emotional responses related to actual or anticipated pain. The scale evaluates three subcomponents: Rumination (inability to stop focusing on pain), Magnification (exaggerating the threat of pain), and Helplessness (feeling unable to cope with the pain).

Each of the 13 items is rated on a 5-point Likert scale, ranging from 0 ("not at all") to 4 ("all the time").

The total score is calculated by summing the scores from all 13 items, resulting in a final score that ranges from 0 to 52. A higher score on the PCS indicates greater pain catastrophizing (a worse cognitive outcome), which is strongly associated with increased pain intensity and functional disability.

The Hospital Anxiety and Depression Scale (HADS) is a 14-item screening tool used to assess the severity of Anxiety and Depression symptoms in medical patients, avoiding confounding physical symptoms. It comprises two subscales: HADS-A (Anxiety) and HADS-D (Depression), each containing 7 intermingled items. Each item is rated on a 4-point Likert scale ranging from 0 ("not at all") to 3 ("most of the time"). The total score for each separate subscale ranges from 0 to 21. A higher score on either the HADS-A or HADS-D subscale indicates greater severity of anxiety or depressive symptoms, respectively. Scores are used both as continuous variables and often categorized for clinical interpretation.

The Tampa Scale for Kinesiophobia (TSK-11) is an 11-item tool used to assess fear of movement, injury, or re-injury (kinesiophobia). It specifically evaluates the patient's belief that physical activity is dangerous or harmful. Each of the 11 items is scored on a 4-point Likert scale, ranging from 1 ("strongly disagree") to 4 ("strongly agree"). The total score is calculated by summing the scores from all 11 items, with some items being reverse-scored to maintain consistency. The final score ranges from 11 to 44. A higher total score on the TSK-11 indicates greater kinesiophobia and subsequent avoidance behaviors, which are linked to increased pain intensity and functional disability in chronic pain populations.

12-item questionnaire that assesses a person's sleep quality and problems over a four-week period. It measures six key areas: sleep disturbance, sleep adequacy, somnolence (daytime sleepiness), snoring, waking due to shortness of breath or headache, and quantity of sleep. The scale yields scores for these six domains, as well as two global sleep problem indices

The International Physical Activity Questionnaire (IPAQ) is a standardized tool that defines and measures physical activity based on frequency and duration over a week. It categorizes physical activity into vigorous-intensity, moderate-intensity, and walking, and also assesses time spent sitting. The IPAQ covers activity across different domains, including work, transportation, domestic chores, and leisure time, to provide a comprehensive picture of a person's physical activit