Research (1) (2) has demonstrated that weakness of specific muscles, and stiffness of the neck joints can both be associated with headache.
Hall and Robinson (1) found that when the upper cervical spine (the top of your neck) does not have the flexibility to rotate as much as normal, you are more likely to suffer from headaches. We can help increase the flexibility of the muscles and joints of your neck with specific mobilisation techniques, massage and exercise.
After completing a study involving 200 patients with and without neck pain, Gwen Jull (2) was able to conclude that both manual therapy by physiotherapists and a specific neck exercise program were both effective in reducing headaches, and that this effect lasted. In other words, physiotherapy joint and muscle treatment was significantly better at reducing headaches than no treatment at all.
(1) T. Hall and K. Robinson: MANUAL THERAPY, Volume 9, Issue 4, pp 197-202 (November 2004)
(2) G. Jull et al: SPINE Bulume 27, Number 17 pp1835-1843, 2002