Value Village ／ Health
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Neck strain from looking down at a smartphone is called "tech neck" around the world. In Japan it spread under the names "sumaho-kubi" (スマホ首, smartphone neck) and "straight neck" (ストレートネック), and you will hear both from colleagues and at the pharmacy. Here we explain what the terms mean and what you can actually do about it.
| Item | Details |
|---|---|
| Weight of the head | About 4–6 kg (roughly 8–10% of body weight) |
| Estimated load on the neck (from a research model) | About 5 kg upright; about 12 kg at 15° forward tilt, 18 kg at 30°, 22 kg at 45°, 27 kg at 60° (Hansraj, 2014) |
| Average smartphone use | About 3–4 hours a day (Ministry of Internal Affairs and Communications survey on media use; over 5 hours for people in their teens and 20s) |
| Guideline for work with display screens | No more than 1 hour of continuous work, with a 10–15 minute break in between; top of the screen below eye level; viewing distance 40 cm or more |
[Verify] The load figures are calculated values from Hansraj KK (Surgical Technology International, 2014), not measurements. Check usage time against the latest Ministry of Internal Affairs and Communications survey.
A reduced curve with no symptoms is not something that needs medical care. What matters is the symptoms (stiffness, pain, headache), and most of these ease with posture and breaks.
Rolling the neck suddenly or with momentum puts load on the cervical spine. Movements that rest the muscles at the back of the neck — tucking the chin slightly, drawing the shoulder blades together, opening the chest — are generally recommended instead.
For long periods your arms tire and the phone drops anyway. What works in practice is elbows against your body, screen between chest and chin height, and at a desk, a stand or riser to lift the screen.
The pillow affects the angle of the neck while you sleep, but the hours spent leaning forward during the day are generally described as having the larger effect. Review both (see our article on pillows).
People in their teens and 20s use phones the most, but in middle age and beyond it overlaps with age-related changes in the cervical spine, so symptoms are described as appearing more readily. Numbness or arm pain is a reason to see a doctor at any age.
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https://www.mhlw.go.jp/content/000539604.pdf
https://www.soumu.go.jp/iicp/research/results/media_usage-time.html
https://www.joa.or.jp/public/sick/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
This article is not meant to diagnose or manage any specific medical condition. If you are worried about your health, see a doctor rather than relying on your own judgement.
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