• 한국전문물리치료학회지
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• 제20권3호
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• pp.19-26
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• 2013

The smart-phone has become a necessity for most people. In this study, we determined that using a smart-phone for 20 minutes can cause increased neck and shoulder muscle activities and fatigue. Seventeen healthy male smart-phone users who attended Yonsei University played a smart-phone game for 20 minutes and changes in their bilateral cervical erector spinae and upper trapezius muscle activities and fatigue were measured. To assess muscle activities and fatigue, we used the following variables: the median frequency, the 50th percentile Amplitude probability distribution function (APDF) value (median load), and the discrepancy in the 90th percentile APDF value and the 10th percentile APDF value (APDF range). A paired t-test was used to compare pre-smart-phone-use status with post-smart-phone-use-status. The median frequency of the bilateral cervical erector spinae and the upper trapezius decreased significantly after 20 minutes of smart-phone use (p<.05). In addition, the 50th percentile APDF value of the bilateral cervical erector spinae and the right upper trapezius increased significantly (p<.05). The APDF range of the bilateral cervical erector spinae and the upper trapezius also increased significantly (p<.05). However, the 50th percentile APDF range of the left upper trapezius was not significantly different (p>.05). These findings suggest that using smart-phones for 20 minutes can induce muscle fatigue and increased neck and shoulder muscle activities.

• 대한인간공학회지
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• 제32권3호
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• pp.273-278
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• 2013

Objective: This study aims to analyze and evaluate fatigue in upper trapezius muscles of adults when inputting text on a smart phone, thereby examining the risk of cumulative trauma disorders in the musculoskeletal system of the upper extremity. Method: Forty-five healthy adults were divided equally into three groups: a smartphone group, a notebook group, and a desktop group. A surface electromyogram was placed on the upper trapezius muscle of each participant, after which they inputted text for ten minutes within an ergonomic setting; their side posture was recorded on video and analyzed. Results: The spectral edge frequency values for the smartphone group, as recorded from the upper right trapezius muscles on the surface electromyogram, showed a significant decrease(p<.05). Regarding the RULA, all three groups had results indicating "action level 2". Conclusion: All three groups had results indicating "action level 2" according to the RULA, which means that additional research on the posture of the participants while performing tasks is necessary, and their posture needs to be corrected. In particular, the smartphone group has the highest levels of fatigue in the upper trapezius muscles, suggesting that the task of inputting text on a smartphone is a high risk for causing cumulative trauma disorders.

• 대한인간공학회지
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• 제34권1호
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• pp.11-18
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• 2015

Objective: The aim of this study was to understand the effects of phone weight on the typing performance and muscle recruitment in the neck and upper extremity while typing a text message with dominant hand. The iPhone4 and iPhone5 were compared due to their 28-gram differences in weight. Background: Too much use of a cellular phone can lead the musculoskeletal disorders in the upper extremity. Phone makers tend to make their new models bigger, lighter, faster and smarter. Method: Fourteen healthy volunteers without any history of neuromuscular disorders or ongoing pain who used their smartphone more than one year were recruited. A 112g phone (iPhone5) and a 142g phone (iPhone4) were used for typing the lyric of the Korean national anthem with their dominant hand. Typing duration, the typing error, the perceived fatigue, and preference was investigated. Muscle recruitment and the resting gap of neck (middle trapezius and levator scapula), shoulder (infraspinatus and mid deltoid), elbow (biceps brachii and brachioradialis), thumb (extensor and abductor policis brevis) were collected using surface electromyography. Typing error was counted and typing speed was calculated in characters per min. The data were analyzed using a paired t-test and chi-square (${\chi}^2$) analysis for the effects of phone weight on the typing performance parameters and muscle recruitment. Results: Typing text message with iPhone5 took longer but had less muscle recruitment in brachioradialis, and extensor policis brevis muscles. Lighter weight of iPhone5 made biceps brachii to rest less without increasing the mean %EMG. Conclusion/Application: Findings of this study can be valuable information for phone designers to develop more productive device and for smartphone users to prevent the musculoskeletal disorders in the upper extremities.

• 대한물리의학회지
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• 제18권2호
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• pp.83-92
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• 2023

PURPOSE: This study examined the effect of using a smartphone according to the direction of wearing a bag on muscle characteristics and balance ability in adults in their 20s with chronic ankle instability. METHODS: Twelve people with chronic ankle instability were examined for three weeks. The types of carrying a bag were classified into three conditions: to the right, to the left, and on both sides. The muscle characteristics and balance ability were measured and analyzed. The one-way ANOVA was used to obtain a difference between conditions. RESULTS: A significant difference in the muscle tone of medial gastrocnemius was observed between the dominant group and the non-dominant group. The muscle tone and stiffness of the peroneus longus decreased significantly after walking with a smartphone and carrying a bag. The maximum slope of the forward and reverse directions increased and decreased significantly, respectively, after walking with a smartphone and carrying a bag on both sides. CONCLUSION: In this study, muscle fatigue causes a decrease in muscle tone and stiffness with chronic ankle instability when carrying a heavy back while walking, and there were asymmetric changes in the balance ability. Therefore, adults with chronic ankle instability should carefully avoid carrying a heavy bag for extended times, irrespective of the style or type of the bag.