The smartphone may weigh only a few hundred grams, but using one can change how much work the neck and shoulder muscles have to perform.
Looking down at a screen commonly combines two movements: the head shifts forward relative to the torso and the neck bends downward. A new biomechanical experiment suggests those positions measurably alter muscular demand—and that the posture people naturally adopt while using a smartphone is much closer to flexed positions than to a neutral neck.
The findings add scientific detail to a problem often reduced online to the phrase “text neck.” The important issue is not that looking at a phone automatically damages the spine. It is that screen position changes the mechanical conditions under which the head is supported, and prolonged exposure may matter when those positions become habitual.
Forward head posture changes the mechanics of holding up the head
Researchers Yi-Lang Chen and Pei-Yong Li examined this directly in a September 2026 Scientific Reports experiment involving 40 young adults—20 men and 20 women.
Participants were tested across five positions: neutral posture, maximum forward-head posture, maximum neck flexion, combined forward-head posture and neck flexion, and natural smartphone use. The researchers measured head and neck movement using motion capture, while surface electromyography recorded activity in the cervical erector spinae and upper trapezius muscles.
The study found that posture significantly affected every measured kinematic variable, muscle activity and discomfort rating, with all posture effects reaching p < 0.001. The combination of forward-head posture and neck flexion produced the greatest cervical flexion, smallest craniovertebral angle and highest activation of the two measured muscle groups.
That result reflects basic biomechanics.
The head has mass, and the neck must continuously generate forces that counter the moment created by that mass. Moving the head farther forward changes its position relative to the cervical spine, while flexing downward changes how muscles and passive tissues share that load.
The September study does not claim that every downward glance causes injury. Instead, it demonstrates that different positions impose different muscular demands.
Natural smartphone use was not mechanically neutral
One of the more useful parts of the experiment was that researchers did not test only exaggerated laboratory postures.
Participants also used a smartphone naturally.
During normal smartphone use, the researchers observed intermediate but appreciable postural and muscular responses that were closer to flexed positions than to neutral. A larger craniovertebral angle—which generally represents a less-forward head position—was associated with lower activity in both the cervical erector spinae and upper trapezius.
That turns smartphone ergonomics into more than a question of whether someone is technically “slouching.”
Where a device is held determines where the eyes need to look. Holding a phone below eye level encourages movement somewhere in the head-neck system so the screen remains visible.
A 2023 kinematic study using wearable inertial sensors found that during smartphone tasks, the largest share of forward flexion occurred around the craniocervical junction. Mean flexion at the C0–C1 region reached about 33.3 degrees while sitting, 27.5 degrees while standing and 32 degrees while walking, while lower cervical segments changed far less.
The body is therefore not bending as a single rigid column. Different cervical regions contribute differently to the posture required to look at a small screen.
Muscle demand can also differ between people
The September 2026 experiment identified another detail that simple posture advice tends to miss.
Female participants showed greater neck flexion and higher cervical erector spinae and upper trapezius activity than male participants, despite having similar craniovertebral angles.
Earlier work by Chen and colleagues reached a related finding. In a 2024 Scientific Reports experiment involving 32 participants, women showed higher neck-muscle activity despite generally smaller neck-flexion angles during several smartphone-use conditions.
That research also found evidence that when head angle exceeded roughly 40 degrees, a cervical flexion-relaxation phenomenon could occur. In deep flexion, some of the mechanical demand may shift away from active extensor muscles toward passive tissues around the cervical spine.
This is one reason a single rule such as “keep your neck below 30 degrees” oversimplifies the problem. Anatomy, posture, task, duration and individual biomechanics all influence what the musculoskeletal system experiences.
Longer phone use is associated with changes beyond the neck
Smartphone posture may also interact with whole-body balance.
A July 2026 study in the Journal of Bodywork and Movement Therapies examined 58 healthy adults aged 18 to 35 and used actual phone-recorded usage time rather than relying entirely on participants to estimate their screen exposure.
Researchers measured neck-flexor endurance, head posture, grip strength and postural control. They found a small but statistically significant relationship between longer smartphone use and greater center-of-pressure variance during both static standing and smartphone-reading conditions. Participants using their phones for more than five hours a day had significantly greater center-of-pressure variance while standing than those with lower use.
The authors concluded that increased usage time was associated with deteriorated postural control, although the study was observational and therefore cannot prove that phone use itself caused those differences.
That distinction matters. Heavy phone users may differ in physical activity, work habits or other behaviors that also influence balance and musculoskeletal health.
Neck pain evidence is stronger than one laboratory experiment
Laboratory biomechanics explain how posture changes load, but population studies help show whether smartphone behavior is associated with symptoms outside the lab.
A 2025 open-access systematic review and meta-analysis pooled seven retrospective studies involving 10,715 participants. Researchers found that people classified as overusing smartphones had 2.34 times the adjusted odds of neck pain compared with participants who were not classified as overusers.
The researchers also emphasized that earlier studies had produced mixed results and that definitions of “smartphone overuse” vary. The association therefore should not be read as proof that smartphones independently cause neck pain in every user.
An earlier open-access biomechanical review similarly found that smartphone use was associated with increased head flexion, forward-head shifting and activity in neck extensor and upper-trapezius muscles, while cautioning that the underlying experimental studies were generally of moderate quality.
Together, those findings create a more defensible picture than the dramatic claim that smartphones are “destroying” people’s spines.
Smartphone ergonomics is ultimately an interface-design problem
The physical consequences of smartphones reveal something product design often overlooks: the interface does not end at the glass.
Screen size, viewing angle, where a device is held and how long an interaction lasts all shape what the body must do to use the product.
That makes ergonomics relevant not only to physiotherapists but also to designers building products that encourage prolonged mobile interaction.
Software cannot determine exactly how someone holds a phone. But products can influence how long people remain continuously engaged, how frequently they stop, whether an activity requires sustained reading and how often users move between devices.
The scientific evidence does not justify panic over every downward glance.
It does justify recognizing that hours of digital interaction are also hours of physical interaction.
A smartphone may be designed around what happens on a five- or six-inch display, but the human body remains part of the system using it. And the farther the head moves away from a comfortable neutral position, the more work that system may have to perform.
