The Ergonomic Concerns for Smartphone Users: Assessment of Muscular Activity, Input Performance and Preference by Various Postures
Date Issued
2014
Date
2014
Author(s)
Ko, Ping-Hsin
Abstract
Background:
In recent years, the demand for smartphones has dramatically increased. However, the health-related ergonomics parameters for smartphone use were not well studied yet. The purpose of this study was therefore set to compare user''s muscle activities, range of motion of joints, text entry performance and posture preference among computer use and smartphone use with various postures.
Materials and Methods:
For comparison, study subjects were asked to type on desktop computer with comfortable sitting posture and on 4-inch-screen smartphone with five different designated postures, respectively, including (1) holding smartphone with right hand without support and typing with right thumb (ST), (2) holding smartphone with suspended left hand and typing with right index finger (SI), (3) holding smartphone with both hands and typing with bilateral thumbs (D), (4) same as (3) but trunk bending forward with forearm lean against leg (DL), and (5) holding smartphone with both hands up to eye level and typing with bilateral thumbs (H).
As the study subjects perform typing, surface electromyogram and goniometers were applied to measure their muscle activities and range of joint motions, respectively, at neck, elbow and wrist. The monitored muscles include flexor pollicis brevis, flexor digitorum superficialis, extensor digitorum communis, biceps brachii, and upper trapezius, which are typically used to flex and extend fingers, to stabilize wrists and elbows, or to support necks and shoulders. Typing performance of the study subject was recorded as maximum correctly typed characters per minute (cpm). Likert’s scale was used to evaluate the muscle symptoms and the preferred postures were ranked in order by the study subject themselves.
Results and Discussions:
(1) Muscle activity
In average, as compared to computer use, the muscle loads for smartphone use with various postures were larger, especially for flexor pollicis brevis, biceps brachii and upper trapezius muscles. Among them, the muscle activity of flexor pollicis brevis muscle was up to 11.3 % maximal voluntary contraction (MVC). As to extensor digitorum communis, the muscle activity for computer use was the highest (7.7 % MVC). In general, users holding smartphone with right hand and typing with right thumb (ST) tended to have much more muscle exertions at various studied muscles.
(2) Range of motion of joints
The angles of cervical flexion of the smartphone users holding with right hand and typing with right thumb (ST), holding with suspended left hand and typing with right index finger (SI) and holding with both hands and typing with bilateral thumbs (D) were generally greater by 15 to 18 degrees as compared with computer use. As to elbow range of motion, the flexion angles for smartphone users with various designated postures were all greater than those for computer use, ranging from 7 to 31 degrees. Especially for those common postures for smartphone use, i.e., holding with right hand and typing with right thumb (ST), holding with suspended left hand and typing with right index finger (SI), and holding with both hands and typing with bilateral thumbs (D), the average ranges of elbow motion were even greater than 90 degrees. As to wrist range of motion, the wrist was always extended either for computer use or for smartphone use with various designated postures. The greatest wrist extension angle, 27 degrees, was found for smartphone use by holding with suspended left hand and typing with right index finger (SI). The wrist extension angles for smartphone use with all other four designated postures were less than that computer use.
(3) Text entry performance
The typing speed of the study subjects when using smartphone ranged from 91 to 115 characters per minute (cpm), which were around half as fast as they did with computer.
(4) Preference
The most preferred posture for typing was computer use(C), followed by smartphone use, holding with both hands and typing with bilateral thumbs (D), then holding with suspended left hand and typing with index finger (SI), holding with both hands and typing with bilateral thumbs, but trunk bending forward with forearm lean against leg (DL), holding with right hand and typing with right thumb (ST), holding with both hands up to eye level and typing with bilateral thumbs (H).
Conclusions:
This study provided objective measurements to illustrate relatively awkward postures while using smartphones, especially the markedly flexed cervical spines and elbows. The corresponding muscle loads for smartphone use were found mostly greater than that for computer use, especially for flexor pollicis brevis, biceps brachii and upper trapezius muscles. Besides, study subjects typed with smartphone about half as fast as they did with computer. The two most uncomfortable postures for smartphone use were holding with right hand and typing with right thumb (ST) and holding smartphone with both hands up to eye level and typing with bilateral thumbs (H). Therefore, when performing large text entry task, computer use is recommended to avoid continuous smartphone use. Meanwhile, it is suggested to intermittently change smartphone-holding postures in order to minimize muscle and joint loads.
Subjects
智慧型手機
觸控螢幕
肌肉活動量
姿勢
表面肌電圖
頸部
大拇指
Type
thesis
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