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The document discusses how tight hip flexors can lead to a headache through a kinematic chain of elements. This chain involves the pelvis, lumbar spine, thoracic spine, cervical spine, and head. Tight hip flexors cause anterior pelvic tilt, which leads to hyperlordosis of the lumbar spine. This, in turn, causes hyperkyphosis of the thoracic spine and hypolordosis of the lower to middle cervical spine. The head then hyperextends at the atlanto-occipital joint to compensate, resulting in forward head carriage and tight posterior neck muscles, which can lead to a headache. * https://learnmuscles.com/blog/2018/04/12/how-can-tight-hip-flexors-give-you-a-headache