Neck flexion is the fundamental movement of the head and neck that allows a person to look downward. This action involves a bending motion of the cervical spine, the segment of the spine located in the neck. Understanding the mechanics and limitations of this movement is important for assessing posture, injury recovery, and overall neck health.
Defining Neck Flexion
Neck flexion is the biomechanical term for the forward movement of the head, bringing the chin toward the chest. This action occurs primarily within the sagittal plane, the vertical line that divides the body into left and right halves. The movement rotates around a medial-lateral axis, passing horizontally through the head. Flexion is the opposite of neck extension, which involves tilting the head backward. This movement requires controlled coordination between the skull and the seven vertebrae of the neck.
Anatomy of the Movement
The movement of neck flexion is achieved by a coordinated effort from several muscle groups located at the front of the neck. The sternocleidomastoid (SCM) muscle is the primary mover for this action, running diagonally across the side of the neck. When both the left and right SCM muscles contract simultaneously, they pull the head into flexion.
Deep to the SCM are the longus capitis and longus colli muscles, collectively known as the deep cervical flexors. These muscles play a supporting role in initiating and stabilizing the movement, particularly in the lower cervical spine. The scalene muscles—anterior, middle, and posterior—also assist in neck flexion, especially when the neck is already tilted to one side. These anterior muscle groups must overcome the resistance provided by the posterior neck muscles, which lengthen and relax to allow the forward bend.
Measuring Normal Range of Motion
The extent of neck flexion, known as the range of motion (ROM), is a standard measurement used in physical therapy and clinical assessments. Healthcare professionals use specialized instruments like a goniometer or an inclinometer to accurately quantify the degrees of movement. These devices measure the angle between the head’s starting neutral position and its maximally flexed position.
The normal ROM for neck flexion in a healthy adult falls between 45 and 80 degrees. A measurement of at least 60 degrees is the minimum acceptable range for healthy function. Assessing this range helps clinicians determine the severity of an injury or the progression of a degenerative condition. A reduced or asymmetrical measurement can indicate muscle tightness, joint restrictions, or nerve impingement requiring further evaluation.
Common Causes of Restricted Flexion
Poor posture is a common cause of restricted neck flexion, particularly the forward head posture known as “text neck.” Sustained periods of looking down at a phone or computer causes the posterior neck muscles to become chronically strained and tight, physically restricting the forward bending motion.
Acute trauma, such as a whiplash injury from a car accident, can cause sudden muscle strain or ligament sprain, resulting in significant pain and limited flexion. Degenerative conditions of the spine, such as cervical spondylosis, can also cause bony changes that physically impede the joints from moving through their full range. Other factors include prolonged sitting, sleeping in an awkward position, and general muscle stiffness.