The goal of this clinical trial is to learn if graded motor imagery can reduce pain sensitivity and period pain in women with primary dysmenorrhea (painful periods with no medical cause).

The main questions it aims to answer are:

1. Is there a decrease in pressure pain threshold (increased pain sensitivity) with graded motor imagery?
2. Is the intensity of menstrual pain reduced by graded motor imagery?
3. Is GMI helpful to reduce menstrual symptoms and pain catastrophizing (negative thinking about pain)?

Researchers will compare full GMI (active intervention), a sham GMI(inactive intervention), and a wait-list (no intervention) to see if GMI works better than the alternatives.

Participants will:

1. Take part in a 6-week graded motor imagery program, sham program, or no intervention control.
2. Do laterality recognition, motor imagery, and mirror therapy exercises in the graded motor imagery group.
3. Complete pain and symptom assessments before and after the program, and again at follow-up.

Women with primary dysmenorrhea have decreased pressure pain threshold (PPT) at local abdominal and lumbar sites and at remote sites (tibialis anterior). This is indicative of central sensitization, rather than just peripheral, prostaglandin-driven pain. This sensitization extends out of the menstrual window and is associated with increased pain catastrophizing (a cognitive-affective amplifier of central pain processing). All of these factors contribute to primary dysmenorrhea being an appropriate target for brain-directed intervention.

Graded Motor Imagery (GMI) is a three-phase physiotherapy program aimed at restoring the normal representation of pain in the cortex and reducing movement-related threat appraisal. Phases progress from implicit motor imagery using left/right body-part recognition tasks, followed by explicit mental rehearsal of pain-free movement. The third phase involves mirror therapy with visual feedback of normal movement. This sequenced approach targets the two measurable mechanisms underlying central sensitization in dysmenorrhea: altered pressure pain sensitivity and elevated pain catastrophizing. GMI has proven to be effective in complex regional pain syndrome, phantom limb pain, and genito-pelvic pain. However, it has not been specifically tested in primary dysmenorrhea.

This three-arm randomized controlled trial compares full GMI, sham GMI, and a wait-list control over six weeks of online-delivered sessions. The sham program is identical to GMI in terms of therapist contact time and structure of sessions, but employs non-pelvic imagery content (to control for non-specific effects of attention and engagement). The outcome is measured at baseline, 6 and 10 weeks by a blinded assessor.

Inclusion Criteria:

1. Female sex (aged 18-30 years)
2. Diagnosis of primary dysmenorrhea confirmed by a physician (painful menstruation for ≥6 consecutive cycles, in the absence of identifiable pelvic pathology on clinical and/or ultrasound evaluation)
3. Pain ≥4/10 NRS experienced during the last period.
4. Confirmed altered pressure pain threshold: PPT ≥2 standard deviations below published norms for age-matched healthy women, measured at baseline assessment
5. Regular menstrual cycle (21-35 days)
6. Capable of engaging in virtual video sessions and taking online tests.
7. Consent to withhold new analgesic or hormonal treatments during the study period.

Exclusion Criteria:

1. Secondary dysmenorrhea (endometriosis, adenomyosis, fibroids, pelvic inflammatory disease, ovarian cysts ≥3 cm confirmed on imaging)
2. Current use of hormonal contraceptives (which alter prostaglandin levels and pain processing)
3. Pregnancy or lactation
4. Concurrent chronic pain condition (fibromyalgia, CRPS, chronic low back pain, chronic pelvic pain unrelated to menstruation)
5. Neurological or psychiatric disorder that would impair motor imagery ability (stroke, schizophrenia, active psychosis)
6. Cognitive impairment affecting informed consent capacity
7. Participation in another clinical trial within 4 weeks before enrollment
8. Previous exposure to graded motor imagery or mirror therapy
9. Regular use of NSAIDs or opioids for non-menstrual indications

Individual participant data will not be shared owing to the confidentiality of study participants as well as the institutional restrictions. De-identified data may be available upon request to the corresponding author after getting institutional's approval.