How Looking at Your Phone Can Lead to Neck Pain

New research shows for the first time that sustained exercise can disrupt the mechanical structure of the neck and increase the risk of neck pain.

Learning new languages, sending emails, attending a virtual class, or talking to loved ones on the other side of the world are just a few of the tasks you can accomplish by pressing a button on a smartphone. Unfortunately, the convenience and usability of modern devices has also come with a painful neck ache.

The sedentary nature of work and prolonged use of portable devices and computers have contributed to a sharp increase in neck pain.

Although it has long been suspected that fatigue in the neck muscles causes pain, it remains unclear what mechanical changes in the spine and muscles precede the weakness.

Now, researchers have discovered that sustained neck strain causes muscle fatigue that subsequently worsens cervical spine curvature, using high-precision x-ray imaging to track spinal movements during neck strain tasks. This leads to neck pain.

Their results appear in the Proceedings of the National Academy of Sciences.

“We’re talking about subtle movements of the neck in static positions, which are difficult to capture. They’re also very complex because there are so many individual pieces in the neck, or what we call motion segments,” said Xudong Zhang, a professor in the department of industrial and systems engineering at Texas A&M University.

“With this study, we have provided the first unequivocal evidence that fatigue causes mechanical changes that increase risk.”

Zhang says this insight can help inform decisions about the way we work and the design of products (such as wearable devices worn on the head) that could potentially reduce the risk of neck pain.

Neck pain is one of the most common musculoskeletal disorders, with approximately 2,500 out of every 100,000 people worldwide having some form of neck pain. In fact, by 2050, the estimated global incidence of neck pain is expected to increase by 32.5%. A major risk factor for neck pain is poor posture that persists for long periods of time. Therefore, working long hours in a hunched position at a computer or using smart devices for extended periods of time are major contributors to neck pain.

Neck posture is maintained dynamically by the bones of the spine being pulled into position by the muscles attached to them. Although the neck is very flexible, it is also very unstable.

“The muscle drives movement by producing force,” Zhang says. “We hypothesized that when the force production capabilities of different muscles decrease, the bone positions change and that can be captured.”

To test their idea, they recruited healthy volunteers to perform a sustained-to-exhaustion neck exercise task. The subjects held their necks in neutral, 40° extended (backward flexed), and 40° forward flexed positions for a period of time. The researchers used electromyography (EMG) to measure the electrical activity of the muscles. In particular, they measured muscle fatigue objectively through changes in the frequency of the EMG signal. In addition, they used high-precision, dynamic X-ray technology to track small-amplitude movements of the cervical spine, which were on the order of a few degrees.

“We envisioned the cervical spine as a cantilever bridge,” Zhang says. “If there is excessive and/or repetitive stress on the bridge, it can sag or buckle; similarly, the cervical spine can sag as the muscles fatigue.”

The researchers’ experimental paradigm validated that sustained exercise does indeed lead to EMG signals of fatigue. Biomechanically, muscle fatigue altered spinal mechanics, which in turn increased the likelihood of injury.

As a next step, the researchers will develop dynamic biomechanical models, a new approach that promises to provide a more realistic understanding of the muscle events that precede fatigue. Unlike the model in this study, which relies on static neck exertion, the dynamic model will capture subtle but consistent changes in the muscles and bones over time.

Funding for this research is administered by the Texas A&M Engineering Experiment Station (TEES), the official research agency of Texas A&M Engineering.

Source: Texas A&M University