Castien R,et al.
J Orthop Sports Phys Ther. 2013 Oct;43(10):693-9. doi: 10.2519/jospt.2013.4868. Epub 2013 Sep 9.

Abstract
STUDY DESIGN: Prospective longitudinal study.

OBJECTIVE: To explore the working mechanism of manual therapy, we investigated whether 3 cervical spine variables were mediators of the effect of manual therapy on headache frequency. Background Manual therapy has been shown to reduce headache frequency in participants with chronic tension-type headache (CTTH). To what extent specific elements of treatment contribute to the effectiveness of manual therapy in CTTH is unknown.

METHODS: One hundred eighty-two participants with CTTH participated in a prospective longitudinal study: 142 underwent manual therapy and 40 participants received usual care by their general practitioner. Regression analysis was performed according to the steps described by Baron and Kenny, and the proportion of mediated effect was estimated for 3 potential mediators: (1) cervical range of motion, (2) neck flexor endurance, and (3) forward head posture. Outcome was defined as a 50% or greater reduction in headache days.

RESULTS: Neck flexor endurance mediated 24.5% of the effect of manual therapy. Cervical range of motion and forward head posture showed no mediated effect.

CONCLUSIONS: Increased neck flexor endurance appears to be a working mechanism of manual therapy. This finding supports isometric training of neck flexors in participants with CTTH.

PubMed Reference:  http://www.ncbi.nlm.nih.gov/m/pubmed/24256171/