Participants will undertake a 6-week therapeutic exercise program, consisting of two sessions per week (12 sessions total), with a primary objective of reducing fibromyalgia's impact on daily life. Each session will involve ten exercises performed in one or two sets each, depending on the week of the protocol. Exercise repetitions and intensity will be individualized using the Borg Rating of Perceived Exertion (RPE) scale (6-20), maintaining an intensity range of RPE 13-17. Specifically, intensity will start at RPE 14 (moderate) in Weeks 1-2, increase to RPE 15 (moderate-high) in Weeks 3-4, and peak at RPE 16 (high) in Weeks 5-6. No external load will be applied during the first three weeks to allow participants to adapt to the program, while progressive resistance will be introduced during the final three weeks according to individual capacity, ensuring a safe and gradual overload.

Measured using the validated Spanish version of the Pittsburgh Sleep Quality Index (PSQI), a 19-item self-report measure evaluating sleep over the past month across seven components. Total scores range from 0 to 21, with higher scores indicating poorer sleep.

Assessed with the Widespread Pain Index (WPI; 0 - 19), the 19 item body map component of the 2016 ACR Fibromyalgia criteria. Participants mark each anatomical region in which they have experienced pain during the previous week; the total score corresponds to the number of painful sites, ranging from 0 (no pain) to 19 (pain in all sites), with higher scores indicating a wider pain distribution and greater disease burden.

Measured with the Symptom Severity Scale (SSS; 0 - 12), the second component of the 2016 ACR Fibromyalgia criteria. Participants rate the severity of fatigue, non-restorative sleep, cognitive problems and extent of additional somatic symptoms on 0 to 3 Likert items (0 = none, 3 = severe). Scores are summed to yield a total ranging from 0 (no symptoms) to 12 (maximal severity), with higher values reflecting a greater symptom severity.

The FSDC total score will be calculated by summing the Widespread Pain Index (WPI) and Symptom Severity Scale (SSS) scores. This yields an aggregate score ranging from 0 to 31, with higher values reflecting a greater overall fibromyalgia symptom burden.

Measured using the Spanish EQ-5D-5L, a validated self-reported tool measuring five dimensions on five severity levels. Responses yield an index score (-0.5 to 1.0), with lower values indicating worse health, calculated using the Spanish value set.

Assessed using the Spanish version of the Hospital Anxiety and Depression Scale (HADS), a 14-item self-report tool comprising two subscales, HADS-Anxiety and HADS-Depression, each scored 0-21. Items are rated on a 4-point Likert scale (0-3), with higher scores indicating greater severity.

Measured using the Spanish version of the 13-item Pain Catastrophizing Scale (PCS), which evaluates the frequency of catastrophic thoughts and feelings related to pain across three subscales: rumination, magnification, and helplessness. Items are rated from 0 to 4, yielding a total score of 0-52, where higher scores indicate greater catastrophizing.

Assessed using the Spanish version of the 16-item Fear-Avoidance Beliefs Questionnaire (FABQ), scored on a 7-point Likert scale (0-6), where higher scores indicate stronger avoidance beliefs.

Assessed using the Spanish version of the Tampa Scale for Kinesiophobia (TSK-11), an 11-item self-report measure of fear of movement and reinjury. Items are scored on a 4-point Likert scale (1-4), with total scores ranging from 11 to 44. Higher scores indicate greater kinesiophobia.

Measured using the Central Sensitization Inventory (CSI), a validated 25-item self-report measure assessing symptoms associated with central sensitization. Scores range from 0 to 100, with scores of 40 or higher indicating the presence of a central sensitization syndrome.

Assessed with a handheld digital algometer (Force One™, Wagner Instruments). Measurements will be taken at two sites: (1) the dorsal surface of the right third finger, midway between the distal and middle interphalangeal joints; and (2) a point 5 cm lateral to the right of the spinous process of the third lumbar vertebra (L3). A 1 cm² rubber tip will apply steadily increasing force until the participant first perceives pain; the force will be recorded in kilograms (kg). Three trials will be performed at each site, with 30 seconds of rest between trials, and the mean of the three readings for each site will be used for analysis. Lower pressure pain threshold (PPT) values (kg) indicate higher pain sensitivity. Higher PPT values indicate lower pain sensitivity.

Measured with a handheld digital algometer (Force One™, Wagner Instruments) applied to the dorsal surface of the right third finger. Ten pressure pulses, each rising at 2 kg·s-¹ to the individual's mean pressure pain threshold, will be delivered at 1 Hz. Participants will rate pain intensity on a 0-10 verbal Numeric Rating Scale after the first and tenth pulses. The temporal summation (TS) score is calculated as NRS₁₀ - NRS₁ (range: -10 to +10), with positive values indicating temporal summation of pain, a marker of central sensitization.

Assessed with a cuff-induced ischemic stimulus on the left upper arm. The cuff is inflated at 20 mm Hg·s-¹ until the first pain sensation, held for 30 seconds, then adjusted to maintain a pain intensity of 3/10 on the Numeric Rating Scale (NRS), and kept inflated. While the cuff remains on, a digital algometer delivers 10 pressure pulses to the dorsal surface of the right third finger: rising at 2 kg·s-¹ to the site-specific mean pressure pain threshold (PPT), held for 1 second, with 1 second of rest between pulses. Pain intensity is rated (0-10 NRS) after the first and tenth pulses. The conditioned pain modulation (CPM) effect is expressed as NRS₁₀ - NRS₁ (range -10 to +10). Lower or more negative values denote weaker endogenous pain inhibition.

Assessed using the 30-Second Sit-to-Stand Test (STS-30), a functional test that evaluates lower limb strength and endurance by measuring an individual's ability to repeatedly rise from a chair without upper limb support over a 30-second period. The total number of repetitions performed during the 30-second period serves as an indicator of functional capacity, with higher scores reflecting better performance.

Assessed using the Timed Up and Go (TUG) Test, a widely used clinical tool that evaluates gait speed, dynamic balance, and overall functional capacity. Participants are timed while rising from a chair, walking three meters, turning around, walking back, and sitting down. Shorter times indicate better functional performance.

Measured using a handheld dynamometer, a widely applied tool for quantifying neuromuscular function in individuals with fibromyalgia. The portable device will be placed just above the ankle while the participant is seated with the knee flexed at 90°, in order to measure maximal voluntary isometric contraction (MVIC) of the quadriceps muscle.

Measured with a Jamar hydraulic dynamometer, according to the protocol described by Hamilton et al. Participants will sit with feet flat on the floor, shoulder adducted and neutrally rotated, elbow flexed at 90°, and wrist and forearm in a neutral position. Three maximal trials will be performed with verbal encouragement, with at least 4-minute rest intervals between attempts. The average of the three trials will be used for analysis.

Motivational regulation was assessed using the Behavioral Regulation in Exercise Questionnaire-3 (BREQ-3), a 24-item self-report instrument grounded in Self-Determination Theory. Each item is rated on a 5-point Likert scale (0 = "not true for me" to 4 = "very true for me"), producing six subscale scores-Amotivation, External Regulation, Introjected Regulation, Identified Regulation, Integrated Regulation, and Intrinsic Regulation-each ranging from 0 to 16. The total raw score ranges from 0 to 96, with higher values reflecting stronger endorsement of the statements. Depending on the pattern of subscale scores, elevated Intrinsic and Integrated Regulation scores indicate more autonomous motivation, whereas higher External Regulation and Amotivation scores denote more controlled or amotivated regulation.

Dizziness will be monitored at every session using a 0-10 Numeric Rating Scale (NRS), where 0 indicates "no dizziness" and 10 indicates "worst imaginable dizziness." Dizziness will be captured as a continuous safety outcome, as it is expected to be the most frequent adverse effect of VR. Documenting its intensity will allow for timely adjustments to the intervention protocol. Higher scores will indicate greater levels of dizziness experienced during VR use.

Pain intensity will be recorded immediately before and after each exercise session using an 11-point Numeric Rating Scale (NRS-11) ranging from 0 ("no pain") to 10 ("worst imaginable pain"). Participants will be asked: "On a scale from 0 to 10, how intense is your pain right now?". Higher scores indicate greater pain intensity. The outcome will be calculated as the within-session change in pain (post-exercise minus pre-exercise score).

Total weekly physical activity will be estimated using the International Physical Activity Questionnaire - Short Form (IPAQ-SF), a 7-item self-report tool validated in Spanish and recommended by the World Health Organization. Participants report the frequency and duration of walking, moderate, and vigorous physical activities over the previous seven days. Minutes of walking are weighted by 3.3 METs, moderate activity by 4.0 METs, and vigorous activity by 8.0 METs. These values are summed to yield a total MET-minutes-per-week score. The possible range is from 0 to no upper limit; higher values indicate greater energy expenditure.