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Investigation of neck muscular load among young adults when using smartphone while walking

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Title
Investigation of neck muscular load among young adults when using smartphone while walking
Author
Han, Hyeseon
Advisor
Shin, Gwanseob
Keywords
Smartphone, neck, head tilt, walking
Issue Date
2019-08
Publisher
Graduate School of UNIST
Abstract
It is widely understood that frequent and prolonged use of smartphones may cause neck-shoulder pain. However, few studies have reported such risks for neck-shoulder problems associated with the use of a smartphone while walking. Because smartphone use while walking is a very common behavior among smartphone users, investigation of relevant ergonomic risks is also necessary. The aim of this thesis research was to investigate potential ergonomics risk factors among smartphone users, especially when using smartphone while walking. This thesis presents a series of cross-sectional and experimental studies that have independent research questions and discusses the results of them in an integrated form. Study 1 was aimed to objectively assess the angle and duration of head-down of smartphone users during a typical working day via naturalistic data collection. Thirty-one asymptomatic young participants conducted their typical activities while their head tilt angle and smartphone app usage records were collected simultaneously for 8 hours. It was found that study participants spent 125.9 minutes (median usage duration) on their smartphones with significantly larger head-flexion angle (p < 0.05) than when they were not using the phone. Head-down posture greater than 30° was found to be more common when using the phone, while mild flexion within the range of 0° to 20° was more common when they were not using the phone. Study 2 was aimed to quantify the head down position when using a smartphone while walking. Head tilt angle was measured from twenty-eight young smartphone users when conducting one-handed web-browsing and two-handed texting while walking a 60-meter outdoor walkway. Study results showed that the median head tilt angle during texting (38.5°) was significantly greater (p<0.05) than that of web-browsing (31.1°), indicating greater static loads to the neck when texting. Participants walked with significantly less (p < 0.05) variation of the head flexion when texting (5.3°) than when browsing (6.8°), and it implies larger efforts of neck muscles to keep the head steadier for texting. Study 3 was aimed to quantify the myoelectric activation (EMG) of neck extensor muscles, head/trunk movement and eye-smartphone position when using a smartphone while walking. Twenty-one asymptomatic young adults conducted three tasks (no smartphone, one-handed web-browsing, two-handed texting) in the laboratory. The mean normalized EMG (NEMG) of the splenius muscles and the cervical erector spinae muscles were 33.3% to 101.8% greater when web-browsing and texting while walking compared to walking without smartphone. Task effect was found in NEMG of splenius of dominant and non-dominant side, NEMG of cervical erector spinae of non-dominant side, head tilt angle, trunk tilt angle, horizontal viewing distance (p<0.05). Also, angular acceleration RMS of neck flexion when normal-walking was significantly higher than other two task conditions. The findings of these three studies indicated that the smartphone use causes substantially flexed head/neck position of smartphone users, which demands the contraction of neck extensor muscles to maintain the head-down posture. The head-down posture and muscle activation during smartphone use may result in neck muscle fatigue or dynamic and static biomechanical loads on the cervical spine and surrounding tissues. Moreover, head-down position and dual-task cost of smartphone users when they are walking on the road may cause another kind of risks such as fall, collision, stability, and traffic safety. Overall conclusion of this thesis would promote awareness of risks of smartphone use to users and support further researches related to health of smartphone users.
Description
Department of Human Factors Engineering
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