Sub-occipital Muscle Inhibition in Tension Type Headache (TTH)

Our primary outcome will consist of changes at each session in self-reported pain, which will be measured with a visual analogic scale (VAS).

Anxiety will be assessed with the State-Trait Anxiety Inventory. This questionnaire is designed for the self-assessment of anxiety (Cronbach's α for this scale ranges from .83 to .92).

The Spanish version of the Headache Disability Inventory (HDI) which has shown a strong consistency/reliability will be used to measure neck disability. The HDI consists of 25 items assessing emotional (13 items) and functional aspects (12 items) with 4 possible response options, the total score ranging from 0 to 52 points and 0 to 48 points for emotional and functional aspects, respectively, with higher scores indicating more disability.

The impact of headache on daily life will be measured by the Headache Impact Test-6 (HIT-6) (Cronbach alpha 0.89; test-retest reliability ranging from 0.78 to 0.90). The HIT-6 consists of 6 items with 4 response options. The total score of HIT-6 ranging from 36 to 78 points, where a higher score indicates a greater impact of headache on the daily life of the respondent.

Upper cervical range of motion will be measured with the CROM-device (Performance Attainment Associates. 958 Lydia Drive, Roseville, Minnesota, USA. 55113) which has demonstrated a good intra-tester reliability for cervical extension, flexion, lateral flexion and rotation. The flexion, extension and lateral flexion ranges of motion will be measured actively with the patient sit in a straight-back chair. The subject will be instructed to move their head and neck through all cardinal planes. The range of motionwill be determined either by the patient reporting the onset of pain or firm resistance met by the evaluator. Three measurements will be done, and the average will be selected for future analysis.

Neck Dissability Index (NDI) is a modification of the Oswestry low back pain disability index, and has the most commonly used self-report measure for neck pain. It is a patient-completed, condition-specific functional status questionnaire with 10 items including pain, personal care, lifting, reading, headaches, concentration, work, driving, sleeping and recreation. The tool is 5-ordinal scale from 1 (I can't) to 5 (I can), with a maximum score 50. The NDI has good reliability and validity in persons with mechanical neck pain.

The SF36 is a shortened version of a battery of 149 health status questions developed and tested on a population of over 22,000 patients as part of the medical outcome study.

BECK II will be used to measure the participant's depression. The Beck Depression Inventory consists of 21 items, assessing depressive symptoms on a Likert scale of 0-3, ranging from 0 = "rarely or not at all" to 3 = "most of the time or always", with overall scores ranging from 0 to a maximum of 63 points.