The Nuchal ligament is the cord like part that runs from the withers to the back of the back of skull. From the wither the nuchal ligament widens of the wither area and blends into the less elastic supraspinious ligament which runs the length of the back under the rider's seat. The nuchal ligaments spans down and attaches to the cervical vertebrae from C2 to C7 Function – when the horse stretches it head forward and down the nuchal ligament gets stretched. In doing so the upper neck muscles will engage which will result in the withers and the ribcage being pulled upwards. This, in turn, makes more room for the pelvic to tilt helping the hind legs to engage (swing).
Problem – clinical signs include permanent resistance against the reins with difficulty or unwillingness to low and flex the head and neck ridden and poor flexion at the poll. Some horses may show tendencies to rear or head shake.
Pressure – pressure it this area from some bridle can cause inflammation to this area aggravating muscles causing resistance.