Range of motion · Neck

How to measure neck range of motion

The neck is the hardest joint on this list to measure from video, and it is worth being plain about why: a pose model has no landmarks on the cervical spine. What it can measure is where the head sits against the trunk. This page explains what that number is, how to film it, and what it leaves out.

The movements

Flexion — bringing the chin down towards the chest.
Extension — tipping the head back to look up.
Lateral flexion — tilting the ear towards the shoulder.
Rotation — turning the head to look over the shoulder.

Reference values

No reference values on this page

The CDC study behind the reference values on the other joint pages did not measure the neck. Rather than borrow a figure from a different method and a different sample, this page quotes none.

How it is measured clinically

Neck range of motion is usually measured with an inclinometer — a gravity-referenced angle gauge, sometimes built into a head-mounted device — or with a goniometer lined up on the head and trunk. Rotation is measured looking down from above, or with a device that tracks the head's turn.

How Markerless measures the neck

The neck angle is made from three points: the nose, the midpoint of the two shoulders, and the midpoint of the two hips. It is the angle at the base of the neck between the line up to the head and the line down the trunk. With the head in line with the trunk it reads 180°, and the distance from 180° is how far the head has moved off that line.

Side-on, it shows the head tipping forwards and back. Front-on, it shows the head tilting to the side. It is one of the joints Markerless calculates from the landmarks rather than measures with the engine, and every figure and download says which.

Head against trunk, not cervical spine

The nose is not a neck landmark. Nodding the head on the top of the neck moves the nose without bending the neck much, and a rounded upper back moves the shoulders without the neck moving at all. The angle describes the head's position against the trunk — useful for posture and for seeing change over time, and a different measurement from cervical range of motion.

How to film it

Side-on for flexion and extension, front-on for side bending.
Put the camera at about shoulder height, square to the person.
Keep the head, shoulders and hips in frame — the hips are part of the trunk line.
Sit or stand still and move only the head, so the trunk line stays put.
Keep the hair off the face and the face towards the side the camera expects.
Film the same way each time.

What video cannot measure

Rotation — turning the head moves the nose towards the camera, not across the picture.
The cervical spine itself — there are no landmarks between the head and the shoulders.
Nodding at the top of the neck separately from bending lower down.
Anything out of the filmed plane, which reads short.

Questions

What is normal neck range of motion?

The CDC reference study quoted on the other joint pages did not measure the neck, so we quote no figure here. Published neck norms exist, mostly measured with inclinometers or head-mounted devices; compare like with like.

Can I measure neck range of motion from a video?

Partly. A side-on or front-on video shows where the head sits against the trunk, and Markerless measures that on every frame. Rotation cannot be measured from a single 2D view, and the angle is head against trunk rather than the cervical spine's own movement.

How accurate is a neck range of motion app?

It depends on the app, the joint and above all the filming. Markerless has not published a validation study against a goniometer or marker-based capture, so treat its neck angles as a consistent measure of what the camera saw rather than a clinical absolute. They are strongest for comparing someone with their own earlier clips, filmed the same way.

Does a neck reading outside the reference range mean something is wrong?

No. Reference values are averages from one study's sample, and individuals vary well beyond them. A number from a video is a measurement, not a diagnosis. If movement is painful or has changed, that is a question for a qualified clinician, not for a chart.

References

Gajdosik, R. L., & Bohannon, R. W. (1987). Clinical measurement of range of motion. Physical Therapy, 67(12), 1867–1872.
A review of goniometry with the emphasis on its reliability and validity: a goniometer reading is itself a measurement with its own error, not a ground truth to compare everything else against.
doi:10.1093/ptj/67.12.1867
Keogh, J. W. L., Cox, A., Anderson, S., Liew, B., Olsen, A., Schram, B., et al. (2019). Reliability and validity of clinically accessible smartphone applications to measure joint range of motion: A systematic review. PLOS ONE, 14(5), e0215806.
A systematic review of how smartphone apps for measuring joint range of motion have been tested for reliability and validity — the place to start if you are choosing one.
doi:10.1371/journal.pone.0215806