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The comparison of muscle activity according to various conditions during smartphone use in healthy adults
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The comparison of muscle activity according to various conditions during smartphone use in healthy adults
Phys Ther Rehabil Sci 2016;5:15-21
Published online March 30, 2016
© 2016 Korean Academy of Physical Therapy Rehabilitation Science.

You Lim Kima, Jaehyun Yoob, Sinwoo Kangb, Taerim Kimb, Namyeol Kimb, Sojeong Hongb, Wonjeong Hwanga, and Suk Min Leeb

aDepartment of Physical Therapy, The Graduate School, Sahmyook University, Seoul, Republic of Korea, bDepartment of Physical Therapy, College of Health and Welfare, Sahmyook University, Seoul, Republic of Korea
Correspondence to: Suk Min Lee, Department of Physical Therapy, College of Health and Welfare, Sahmyook University, 815 Hwarang-ro, Nowon-gu, Seoul 01795, Republic of Korea, Tel: 82-2-3399-1632, Fax: 82-2-3399-1639, E-mail: leesm@syu.ac.kr
Received February 1, 2016; Revised March 16, 2016; Accepted March 17, 2016.
cc This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract

Objective

The purpose of this study was to see the changes in muscle activity of the upper limb in persons using a smartphone.

Design

Cross-sectional study.

Methods

An experiment was conducted to target 15 right-handed university students. Experiments were carried out for students using cell phones for more than a year. In this study, experiments were carried out with one-handed and both handed operation of smartphone use in a sitting position, the same parameters with smartphone use in a standing position. The experiments were carried out by having the subjects write a text message in Korean on the smartphone for 3 minutes repeated 3 times with a rest period of 10 seconds given between each 3 minute period. Electromyography (EMG) was used to record the muscle activity of the upper trapezius (UT), extensor carpi radialis (ECR), and abductor pollicis (AP) during phone operation.

Results

The muscle activity of the AP and ECR were significantly higher during single handed compared to double handed in both sitting and standing position (p<0.05). The muscle activity of the ECR was significantly higher in standing position compared to sitting position with double handed use of the smartphone (p<0.05). UT muscle activity of the right has been activated more than twice compared to the left UT in a sitting position (p<0.05). And UT muscle activity on the right has been activated more than five times compared to the left in a standing position (p<0.05).

Conclusions

Using smartphone with double hand is useful for the prevention of musculoskeletal disorders.

Keywords : Electromyography, Muscle activation, Smartphone
Introduction

As of July 2015, there are 42,318,776 people smart phone users in Korea, which means that 79.7% of the mobile phone users in Korea are using smart phones, and this number is in the increasing trend since December 2011 [1]. As reflected by the numbers, one can easily witness the use of smart phones while using the subway, the bus, walking on the road and even when driving.

Studies concerning smart phones use were conducted to measure user convenience [2,3] focusing on the models of the smart phone as well as studies concerning finger typing while using smart phones [4,5]. However, as the interest on the physical influence of the smart phone users have increased recently, studies on the addiction phenomenon due to smart phone use are more prevelantly presented [6?8]. Although the use of touchscreen smartphone involves low forces from fingers or thumbs, there may still be substantial loading among the postural muscles holding the handheld electronic device, especially when the touch action is performed with high speed and high repetition rates.

In particular, in the study of the Eom et al. [9]. 18.8% experienced symptoms of musculoskeletal disorders using smartphones. Finger and wrist pain was the majority of symptoms found that was most appealing. Moreover, there were studies that reported that musculoskeletal disease gets more severe by the increase in usage hours of smart phones [9?11]. Especially, people who engage in increased smart-phone usage and usage time had more experience in wrist and finger-related diseases [10].

The use of smart phones is exposed to repetitive strain injury (RSI), one of the musculoskeletal diseases. RSI syndrome is a disease that may occur with when repeated use of specific parts of the body (nerves, ligaments, muscles, etc.) is damaged and then, the damage occurs cumulative [12]. RSI syndrome is associated with the hands with overly repetitive finger use, as if you are writing a text message. This fact is relevant enough in order that terms such as text message injury, blackberry thumb, iphone thumb are made [13].

Users who use cell phones by carrying them in their hands have reported discomfort at least in one part of the upper limbs, upper back, or neck [14,15]. Also, using smart phones for a long time induces musculoskeletal symptoms by giving consistent mechanical stress to the tendon, muscle and organs [8,14,16].

There is many research on the usage of smart phones but there is still a lack of studies on muscle activity in sitting and in standing and muscle activity when using smart phones with one hand or both hands. This study will compare and analyze the muscle activity of the upper limb in four postures using a smart phone with one hand while standing, using a smart phone with two hands while standing, using smart phone with one hand in sitting, and using a smart phone with two hands in sitting.

This purpose of this study is to observe the change of the muscle activity of the upper limb in two postures using smart phones. To achieve the purpose of the study the muscle activity of the upper limb that changes by posture using smart phones will be compared and analyzed using electromyography (EMG) analysis.

Method

Subject and procedure

From November, 1 to 30, 2015, an experiment was conducted with the consent to research to target 15 right-handed S college students, who are use a smart phone. In this study, an experiment was conducted to target the 15 right-handed university students. And experiments were recruited for people using cell phones for more than a year. They were between 20?27 years of age. Their mean height was 173.03±2.05 cm, and their mean body weight was 68.6±6.50 kg. Exclusion criteria were any limitations in upper extremity movement or a history of upper extremity orthopedic problems in the last 6 months. Experiments were excluded if subjects had a positive sign to the Phalen’s test [17]. This study was approved by the Institutional Review Board of Sahmyook University.

In this study, experiments of one-handed holding a smart phone with sitting position, while both hands holding the smart phone in a sitting position, the experiment of holding a smart phone one-handed in a standing position, both hands holding a smart phone in a standing position. These 4 experiments were carried out by having the subjects writing a text message in Korean on the smart phone for 3 minutes repeated 3 times. Rest times of 10 seconds were given between each 3-minute period where the subject was writing the text message. Each time the posture was changed, in order to prevent fatigue, subjects were given 5 minutes of rest. And the order of the posture implemented was proceeded in random order (Table 1) [16].

For the sitting posture, the test was implemented in a height adjustable chair that was height fitted according to the height of the subject, and the subjects were asked to sit in a naturally hunched posture without their back touching the back of the chair. In the standing posture, the height of the paper with the writing was controlled by the eye-level of the subject and a 3-minute rest to avoid exhaustion when changing postures was implemented. By preparing 4 types of famous sayings of 25 sentences each which totals of 100 sentences, the change of muscle activity by learning effect was avoided. In the posture of executing the assignment with one hand in sitting, the hand that held the smart phone was located on the same side thigh and the paper with the famous saying was located on the opposite thigh. In the sitting posture of executing the assignment with the use of both hands, both hands were put together naturally resting on each thigh and the smart phone was located on the middle of the two thighs while the paper with the famous saying was fixed at the height of the thighs. In the posture of executing the assignment with one hand standing, the forearm was fixed to the upper body naturally and the other hand was in the resting posture naturally to the side of the body and when in the posture of executing with two hands in standing, both fore arms were fixed to the upper body naturally and the cell phone was plated in the middle of the body.

The degree of the neck in wrist maintained a neutral position (the degree of the wrist was from 0?20 degrees) (Figures 1, 2).

When executing the experiment with one hand, the dominant hand executed the experiment and with the model of the cell phone not being controlled, in the case that the subject had difficulty executing the experiment with one hand, an IPhone 6s was used as the cell phone to execute the experiment in all postures. The qwerty and Chonjiin Hangul keyboard was used on the smart phone and the predictive message function was not used (Figure 3).

Outcome measure

The EMG demonstrated reliability as well as inter-examiner reliability especially the reliability of the tester [18]. In addition, rather than a static posture, under the influence of less reliability, the dynamic experiment was better intraclass correction coefficient ≥ 0.75 [19]. Surface electromyographys (sEMG) sensitivity and accuracy of dynamic movements was about 88.8% therefore 81.3% of the results were meaningful. And when flexion-relaxion was measured, we were able to accurately distinguish back pain and a healthy person’s back [20].

The EMG machine that was used in this study is a very sensitive machine, therefore, all the test subjects were cleaned with alcohol swabs before being attached to the EMG. While executing the experiment, muscle activities of upper trapezius (UT), abuductor pollicis (AP), extensor carpi radialis (ECR) was measured using the EMG [10,16,21?23].

The Noraxon EMG System (Noraxon USA Inc., Scottsdale, AZ, USA) was used. EMG signals were sampled at 1,000 Hz, and band-pass filtered between 20?450 Hz. The root mean square (RMS) of the signal was calculated, and were normalized to the EMG data maximum voluntary contraction (MVC) [16].

In this study 3 pairs of surface electrode were attached to the hands, upper limbs and trapezius muscle of the subject. The ground electrode was accurately attached attached to the C7 process, UT was attached laterally 2 cm from the mid point of the C7 process and acromion. ECR was attached 2 cm below the elbow in the posture where the forearm is prone. The electrodes that were attached to the two muscles were the same as illustrated in the sEMG manual [22] and the AP was attached on the muscle belly parallel with muscle fibers (Figure 3) [24].

The same test was administered to the researcher for 3 times each for 5 seconds for reliability of the MVC. UT measured shoulder elevation, AP the thumb abduction, and ECR to the wrist extension. Posture was consistently in a naturally hunched posture without their back touching the back of the chair in all measurement of MVC.

Data analysis

Experiments were administered for 3 minutes was repeated 3 times. The average was calculated and then converted into %MVC. The ground electrode was placed at the seventh cervical vertebra (C7). EMG signals 20?450 Hz. The RMS of the signal was calculated, and were normalized to the EMG data maximum voluntary isometric contraction [16]. All statistical analyses were performed using SPSS software ver. 12.0 (SPSS Inc., Chicago, IL, USA). One-way repeated-measures ANOVA were used to compare one-handed and two-handed use. And paired t-test was used to compare right and left muscle activity.

Results

Muscle activities of the UT, AP, and ECR were significantly different in both single-handed and double-handed smartphone use (p<0.05). Also ECR muscle activities were significant in sitting and standing position (Tables 1, 2) (Figures 4?7).

Smartphone with single-handed use also resulted in increased muscle activities in the UT during sitting and standing position and ECR during sitting position. The right UT muscle activity was activated more than twice than the left UT in the sitting position (p<0.05). And the right UT muscle activity was activated more than five times than the left UT in the standing position (p<0.05) (Table 3, Figure 8).

Discussion

Few studies have focused on the actual methods of handling smart phones, although it is known that the muscle activity demands of one-handed use are greater than those of operation with both hands [14?16]. In the study of Lee et al. [16], the muscle activity of UT, ECR, AP was compared when executing the experiment holding a cell phone with one hand and two hands while sitting. The present study was proceeded comparing not only in sitting but also including the posture of using smart phones while standing which could be seen easily in usual time such as in public transportation.

Even though there was larger muscle activity on both sides of UT and ECT while standing as in the prior study [16,24] among the 6 muscles, but left AP did not get influenced in the standing posture and the right AP was larger while in sitting.

Such result shows that the actual muscle activity of the AP muscle is not influenced by standing or sitting, but is rather influenced by whether the muscle is used for texting or not. Kim et al. [21] found consistent findings when entering text into mobile phones, AP muscles was found to have the highest fatigue.

In the findings of the left AP, the muscle activity was the largest while implementing the experiment with both hands, but demonstrates that there was a small influence in the posture as there was no significant difference when executing the experiment with two hands.

In the findings of the right AP also, texting with one hand without the assistance of the left hand in sitting was larger than the case typing with one hand in standing, but the point where the difference of the two methods were not significant shows that there is a bigger and more clear influence in typing with two hands or one hand rather than a difference in posture.

As the study from Lee et al. [16], UT among the measured muscles act as the stabilizer of the upper limb and ECR and AP which are the remaining muscles also play an important role in the stability of the wrist, therefore shows that muscle activity grows more when using a smart phone with two hands in the right AP, right ECR, right UT to compensate for the instability of the wrist and shoulder when using the smart phone with one hand. However, this study showed a significant difference in the right ECR muscle and right AP, but there was no significant difference in the right UT. This is thought that the in the right ECR and right AP, the muscles are activated by the instability of the wrist when using the cell phone with one hand in standing, therefore we can consider that there is slight instability in the shoulders of the subjects.

Also, in case of the left UT, it showed the largest findings when executing the experiment with two hands while standing, but demonstrated the smallest findings while executing the experiment with two hands. This is thought that there is no big instability of the shoulder that could increase the activity of the left UT when using a smart phone with two hands in sitting as the left UT is activated to compensate for the instability of the shoulder. In case of the left AP, the left ECR demonstrated a larger finding when executing the experiment with two hands.

This is a result as the left muscles were used while executing the experiment with two hands while the left AP and left ECR muscles were not used when executing the experiment with one hand.

From the results, it was discovered that the muscle of the upper limb was differently activated by the posture using smart phones. In the prior study there was uncomfortableness in at least one part from upper limb, upper back, and neck when using carrying cell phones in the hand [14?16] and this goes the same with the result of this study. Also, the excessive usage of smart phones lowers the threshold of the pain, which means pain related with musculoskeletal disease will be inducted as the usage of smart phones increases [11,25]. Therefore, at the point where there is increase of us age of smart phones and increase of musculoskeletal disease patients, the posture must be considered significantly. This is because that static and dynamic posture while using smart phones could be the potential factor in the musculoskeletal disease of the modern people.

Therefore, it will be of help to prevent musculoskeletal disease by using smart phones with two hands in sitting rather than giving burden to the upper limb using smart phones with one hand while standing. At first, the purpose of this study tried to look into the relativeness of the muscle activity by posture and the use of both hands with use of a smart phone and we found significance in the study, and we hope to act as the basic data on the relativeness of the musculoskeletal diseases by using smart phones.

For limitations of this study, firstly there were not many subjects that participated in the research. There were more female students than male students therefore we were unable to match the gender ratio. Secondly, the study studied on only two postures using the smart phones which is sitting and standing. Finally, it is deemed that there was overall tiredness by long test hours.

Figures
Fig. 1. One-handed smartphone use (A) double handed use (B) in a sitting position.
Fig. 2. One-handed smartphone use (A) double handed smartphone use (B) in a standing position.
Fig. 3. Electromyography attachment sites. UT: upper trapezius, ECR: extensor carpi radialis, AP: abductor pollicis.
Fig. 4. Comparison of left muscle activities of one-handed and double-handed smart phone use and posture. %MVC: % maximum voluntary contraction, UT: upper trapezius, AP: abductor pollicis, ECR: extensor carpi radialis. Significant difference between one and double-hand. *p<0.05.
Fig. 5. Comparison of right muscle activities of one-handed and double-handed of smart phone use and posture. %MVC: % maximum voluntary contraction, UT: upper trapezius, AP: abductor pollicis, ECR: extensor carpi radialis. Significant difference between one and double-hand. *p<0.05.
Fig. 6. Comparison of left muscle activities of sit and stand position smart phone use and posture. Significant difference between sit and stand. %MVC: % maximum voluntary contraction, UT: upper trapezius, AP: abductor pollicis, ECR: extensor carpi radialis. Significant difference between one and double-hand. *p<0.05.
Fig. 7. Comparison of right muscle activities of sit and stand position of smart phone use and posture. Significant difference between sit and stand. %MVC: % maximum voluntary contraction, UT: upper trapezius, AP: abductor pollicis, ECR: extensor carpi radialis. Significant difference between one and double-hand. *p<0.05.
Fig. 8. Comparison of left and right double-handed use smart phone. %MVC: % maximum voluntary contraction, UT: upper trapezius, AP: abductor pollicis, ECR: extensor carpi radialis. *p<0.05.
Tables

Table 1

Comparison of left muscle activities of single-handed and double-handed smartphone use and posture (N=15)

Left musclePosture
SitStand
One-handed useUT0.17±0.150.18±0.15
AP0.19±0.15***0.22±0.13***
Double-handed useECR0.22±0.18*0.24±0.19***
UT0.13±0.060.21±0.19
AP1.43±0.831.35±0.87
ECR0.42±0.240.52±0.21

Values are presented as mean± (% maximum voluntary contraction). UT: upper trapezius, AP: abductor pollicis, ECR: extensor carpi radialis.

*p<0.05,

***p<0.0001,

p<0.05.

*Significant difference between one and double-hand.

Significant difference between sit and stand.


Table 2

Comparison of right muscle activities of single-handed and double-handed smart phone use and posture (N=15)

Right musclePosture
SitStand
One-handed useUT0.46±0.451.15±1.31
AP3.46±1.83***3.29±1.69***
ECR0.50±0.23*0.69±0.43***
Double-handed useUT0.26±0.131.04±1.23
AP1.46±0.811.46±0.97
ECR0.32±0.170.52±0.40

Values are presented as mean± (% maximum voluntary contraction). UT: upper trapezius, AP: abductor pollicis, ECR: extensor carpi radialis.

*p<0.05,

***p<0.0001,

p<0.05.

*significant difference between one and double-hand.

significant difference between sit and stand.


Table 3

Comparison of left and right double-handed use smart phone use (N=15)

MusclePostureLeftRight
SitUT0.13±0.060.27±0.13*
AP1.43±0.841.45±0.81
ECR0.42±0.250.32±0.17*
StandUT0.21±0.201.05±1.23*
AP1.35±0.881.47±0.98
ECR0.52±0.210.53±0.41

Values are presented as mean± (% maximum voluntary contraction). UT: upper trapezius, AP: abductor pollicis, ECR: extensor carpi radialis.

*p<0.05.


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