Examination of muscular pain when using an innovative smartphone app for adults

1 Introduction

At present, smartphone technology is frequently used in daily life in all age groups. This is mainly due to the smartphone’s portability and ease of access to communication. In 2018, there were reportedly 57 million smartphone users in Thailand, with a 24% increase in Internet users in that year [1]. Moreover, it was found that Thai users spent more time “surfing” the Internet compared to the previous year, with an average of approximately 10 hours per day, whereas smartphone users from around the globe averaged approximately 5 hours per day. The heaviest users were between 18 and 37 years old [2]. Smartphone usage worldwide is so heavy that the term “phubbing” [3] has been introduced to describe a preference for smartphone use over face-to-face interaction. Users around the world gravitate to the “Mobile First” concept as people tend to utilize smartphones more than traditional computers when surfing the Internet. This is due to the fact that mobile application software is being constantly developed with the intention of taking advantage of the form factor’s unique features and attempting to satisfy consumers’ needs [4, 5].

Research has shown that using smartphones over long periods of time can lead to musculoskeletal pain. Neck pain is most commonly seen [5–9], with additional pain in the shoulders, upper back, arm, and hands [10]. Awkward postures while using a smartphone can cause musculoskeletal pain effects. The postures most likely to cause these effects are neck flexion (82.74%), knee flexion (67.81%), back flexion (67.50%), elbow flexion (65.15%), hip flexion (37.95%) and wrist flexion (22.40%) [10]. These postures can cause neck pain (68%), upper back pain (62%), right elbow and lower arm pain (32%), left elbow and lower arm pain (27%), right shoulder pain (52%) and left shoulder pain (46%) [8]. Furthermore, heavy smartphone use can induce visual problems: eye pain (76.2%), eye strain (75.75%), blurry vision (60.5%) and double vision (40.5%). These symptoms are prevalent when smartphones are overused with up-close viewing and glare [11–15]. When users stare at the screen, blinking becomes less frequent, causing dry eyes and soreness [16].

Operating smartphones with good ergonomics is key. Spending less time on smartphones and taking short breaks is highly recommended [17, 18]. Prior research has shown that improving posture by using smartphones with the neck in a neutral position [19–23], sitting upright [24], holding the phone with two hands [26, 27] or finding an armrest, if available [22, 23], using a backrest or cushion [25], blinking frequently, adjusting the brightness [11, 16], holding the smartphone farther away from the eyes at approximately 30-40 cm [15, 28], and stretching muscles [29, 30] helps to prevent musculoskeletal disorders in users.

Applications for smartphones have been developed and designed for adult users to prevent musculoskeletal pain, e.g. MAKE A MOVE [31], Office Syndrome [32], and ILO Ergonomic Checkpoints [33]. However, these applications are difficult to use due to certain weak points. The main weak point is that they do not use pop-up notifications to inform users in real time that they should adjust to correct posture, have frequent breaks, remind users to blink regularly, hold the phone with two hands away from eyes at approximately 30-40 cm, and stretch muscles. Also, not all of the information in these apps is ergonomically sound for users. A previous study discovered that a smartphone application designed to encourage good posture practice for children significantly decreased musculoskeletal pain in users aged 10-12 by providing information via cautionary warnings. This helped to considerably reduce pain compared to the “no app use” group [34]. The aim of the current study was to study pain in the neck, shoulders, upper back, lower back, arms, hands, and eyes regions comparing “app use” and “no app use” conditions in smartphone users aged 18-25 years old for 15, 30, and 45 minutes.

2 Methods

2.1 Participants

Thirty healthy participants aged 18–25 years old were recruited to participate in the study. The study was approved by the Human Ethics Committee of the first author’s university. Inclusion and exclusion criteria are listed in Table 1. Participants followed the process of data collection shown in Fig. 1. Means and standard deviations of age, weight, height, and BMI in the smartphone usage study were 21.5±1.1 years, 56.5±8.1 kg, 166.0±8.9 cm, and 20.4±1.4 kg/m², respectively.

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Table 1

Inclusion and exclusion criteria

Inclusion criteria	Exclusion criteria
1. Asymptomatic pain in the neck, shoulder, upper back, lower back, arm and hands that requires regular visits to the doctor or physical therapist within one month prior to the experiment [35]	1. History of spinal, hip and hand surgery [38]
2. Age 18-35 years old	2. Visible spinal scoliosis [38]
3. Normal BMI, 18.5-22.9 kg/m2 [36]	3. Infectious disease or cancer of the spine
4. Experience with smartphone use with at least 5 hours/day of the usage [37]
5. 202/20 vision or vision corrected by glasses [27]

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Fig. 1

Posture during smartphone use: “no app use” and “app use” condition.

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Diagram 1

Data collection process.

2.5 Application

The target OS is Android. The application does not interfere with any functions of the smartphone. The smartphone app (Fig. 2) consists of two components, as outlined below.

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Fig. 2

Information for smartphone users in the app (A) and pop-up screen warning (B).

1) Information to encourage good posture, hold the device properly, relax shoulders, take frequent breaks, rest the eyes

The information section was accompanied with photos and text used to encourage the user to use the smartphone with correct posture. The reasons for sitting with good posture during smartphone use were also explained before the study began. If users were in a slouching position, they were reminded to correct their posture; holding the device using two hands at chest level with relaxed shoulders and arms beside the body was recommended. They were also recommended to place the smartphone at least 30-40 centimetres away from the eyes [15, 28]. Tasks to perform during frequent breaks (every 15 minutes with short duration) and long breaks, including standing up and walking, were given to the participants. Participants were also instructed to blink their eyes with regular repetitions of 12-15 times and to rest their eyes every 15 minutes by gazing ahead approximately 3 meters. In addition, participants were shown how to effectively stretch muscles in many regions related to smartphone use, with guided photos of each muscle and instructions to maintain normal muscle length. Participants were informed of adjustable light tones on their smartphones and how to properly use the light tones to ease their eye strain.

Notifications were shown at the top left corner of the smartphone screen with clear and neat text, photos, and a pleasant prompt sound. It was imperative to include with every pop-up reminder to sit with correct posture during smartphone use. At the start of the study, users were reminded to handle the smartphone with both hands approximately 30-40 cm from the eyes, and to use the available arm rests. They were advised to rest their eyes by gazing ahead approximately 3 meters for 15 seconds during rest intervals. They were also asked to blink their eyes at least 15-20 times per minute. The pop-up screen warning began when users clicked on the app icon to launch it. After that, the warning was shown every 15 minutes until the last warning of 45 minutes. Mainly, the warning was about correct sitting posture, rest eyes, relaxed shoulder, handle smartphone at chest level and frequent break of 2 minutes.

2.5.1 Statistical analysis

Normality of the distribution of participant’s reported pain severity levels was analyzed with a Komogorov Smirnov test. Hypothesis tests comparing the pain between “app use” and “no app use” were pre-planned and analysed using a two-way repeated measures ANOVA with post hoc analysis using Bonferroni correction. The statistical analyses were run in SPSS version 23.0 for MacOS.

3 Results

3.2 Severity of pain in “app use” and “no app use” condition during smartphone use

The results showed that neck, shoulder, upper back, arm and hand pain in the “app use” condition was significantly lower than in the “no app use” condition, with p-values of 0.007, 0.007, 0.020, 0.050, and 0.024, respectively (Graph 1, Table 3).

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Graph 1

Severity of pain at neck, shoulders, upper back, lower back, and arms and hands in “app use” and “no app use” conditions at 0, 15, 30, and 45 min.

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Table 3

Comparison of severity of pain in “app use” and “no app use” condition during smartphone use

Region	Df	Sums of squares, type Ill	Mean square	F statistic	P-value
Eye	3	6.961	2.320	2.381	0.071
Neck	3	9.695	3.232	4.190	0.007*
Shoulder	3	9.665	3.222	4.145	0.007*
Upper back	3	7.591	2.530	3.355	0.020*
Lower back	3	1.907	.636	.836	0.475
Arm	3	4.922	1.641	2.645	0.050*
Hand	3	5.321	1.774	3.217	0.024*

^*Two-way repeated measures ANOVA with p-value of 0.05.

2) Pop-up screen warnings

Neck pain in the “app use” condition was significantly lower than in the “no app use” condition at 15, 30, 45 min, with p-values of 0.025, 0.001, 0.001, respectively, with means and standard deviations of severity of pain at 15 min being 0.9±1.4 vs 1.5±1.5. At 30 min, they were 1.5±1.6 vs 2.2±1.8, and at 45 min, they were 1.8±1.9 vs 2.8±2.0. Details are summarized in Graph 1, Table 3.

Shoulder pain in the “app use” condition was significantly lower than in the “no app use” condition at 15, 30, 45 minutes, with p-values of 0.002, 0.001, 0.001, respectively, with means and standard deviations of severity of pain at 15 minutes being 0.9±1.1 vs 1.7±1.5, at 30 minutes, 1.3±1.4 vs 2.4±2.0, and at 45 minutes, 1.7±1.9 vs 3.1±2.1 (see Graph 1, Table 3).

Upper back pain in the “app use” condition was significantly lower than in the “no app use” condition at 15, 30, and 45 minutes, with p-values of 0.001, 0.002, and 0.001, respectively. Means and standard deviations of severity of pain at 15 minutes were 0.4±0.7 vs 1.0±1.4, at 30 minutes, 0.8±1.2 vs 1.6±2.0, and at 45 minutes, 1.1±1.6 vs 2.1±2.1 (see Graph 1, Table 3).

Arm pain in the “app use” condition was significantly lower than in the “no app use” condition at 15, 30, and 45 minutes, with p-values of 0.018, 0.014, and 0.002, respectively. Means and standard deviations of severity of pain at 15 min were 0.2±0.6 vs 0.6±1.4, at 30 minutes, 0.6±1.1 vs 1.1±1.7, and at 45 minutes, 0.7±1.4 vs 1.6±2.0 (see Graph 1, Table 3).

Hand pain in the “app use” condition was significantly lower than in the “no app use” condition at 15, 30, and 45 minutes, with p-values of 0.031, 0.005, and 0.004, respectively, with means and standard deviations of severity of pain at 15 minutes being 0.2±0.4 vs 0.6±1.0, at 30 min, 0.5±0.9 vs 1.2±1.7, and at 45 minutes, 0.7±1.2 vs 1.5±1.9 (see Graph 1, Table 3).

However, there was no significant difference in eye and lower back pain between the “app use” and “no app use” conditions.

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Table 4

Comparison of severity of pain in “app use” and “no app use” condition at 15, 30, and 45 minutes

Time	Situation	Pain scale at seven regions (total pain sore = 10)
		Eye pain	Neck pain	Shoulder pain	Upper back pain	Lower back pain	Arm pain	Hand pain
0 min	No app use	0.2±0.8	0.5±12	0.9±1.4	0.4±0.8	0.7±l.4	0.2±0.8	0.1±0.6
	App use	0.2±0.6	0.5±1.3	0.6±1.2	0.3±0.6	0.2±0.7	0.0±0.2	0.0±0.2
	Paired T-Test	p = 0.867	p = 0.989	p = 0.161	p = 0.156	p = 0.014*	p = 0.187	p = 0.185
15 min	No app use	0.8±I.I	1.5±1.5	1.7±1.5	1.0±1.4	1.1±1.4	0.6±1.4	0.6±1.0
	App use	0.5±0.8	0.9±1.4	0.9±1.1	0.4±0.7	0.6±0.8	0.2±0.6	0.2±0.4
	Paired T-Test	p = 0.030*	p = 0.025	p = 0.002*	p = 0.001*	p = 0.005*	p = 0.018*	p = 0.031*
30 min	No app use	1.6±1.9	2.2±1.8	2.4±2.0	1.6±2.0	1.7±1.9	1.1±1.7	l.2±1.7
	App use	1.0±1.3	1.5±1.6	1.3±l.4	0.8±1.2	1.1±1.3	0.6±1.1	0.5±0.9
	Paired T-Test	p = 0.001*	p = 0.001*	p = 0.001*	p = 0.002*	p = 0.005*	p = 0.014*	p = 0.005*
45 min	No app use	2.2±2.3	2.8±2.0	3.1±2.1	2.1±2.1	2.3±2.2	l.6±2.0	1.5±1.9
	App use	1.3±1.8	1.8±1.9	1.7±1.9	1.1±1.6	1.4±1.7	0.7±1.4	0.7±1.2
	Paired T-Test	p = 0.001*	p = 0.001*	p = 0.001*	p = 0.001*	p = 0.001*	p = 0.002*	p = 0.004*

*Post hoc analysis with Bonferroni correction, significant difference with p value of 0.05.

This study focused on the evaluation of a smartphone application developed to help reduce the risk of musculoskeletal pain in adults aged 18-25 years old. The application consists of helpful examples of correct posture while engaging with smartphones. These pieces of information are distributed via pop-up screen warnings that appear on the screen; recommendations include keeping the neck in a neutral position or at a slight neck flexion, sitting upright, holding the phone with two hands or finding an armrest if available, relaxing shoulders and arms, taking frequent breaks, and holding the smartphone 30-40 cm from the eyes when using the smartphone for 45 minutes or more.

The results of the study show that neck, shoulder, upper back, arm, and hand pain in the “app use” condition was significantly lower than in the “no app use” condition at 15, 30, and 45 minutes (Table 3, Graph 1). This is due to the fact that users operating the smartphone with the application open receive information about proper posture adjustments, such as keeping the neck in a neutral position or sitting with a slight neck flexion and holding the phone with two hands and sitting upright to straighten the angle of the neck.

The survey found that 100% of participants followed the notifications about holding the smartphone with both hands at chest level while sitting upright. As a result, neck pain was reduced. Intolo et al. found that putting the neck in a neutral position or slight neck flexion during smartphone use eased tension on the neck extensor and upper trapezius muscles when the smartphone was placed on the lap or a posture that caused the neck to flex unnaturally [6, 20]. In relation to this discovery, Dennerlein and Gustfsson found that holding a smartphone with two hands at chest level in a seated position helped users correct their head and neck posture from a tilting neck flexed posture to a neutral posture, which subsequently worked less of the neck extensor muscle [22, 23]. In a well-seated posture, the lumbar region, thorax, and neck are at neutral positions, which results in less load on the lumbar region, thorax, and cervical spine, along with less muscle activity in the neck extensors.

Shoulder pain in the “app use” condition was significantly lower than in the “no app use” condition at 15, 30, and 45 minutes. This is explained from the results of having a straight spine and relaxed shoulders while using the smartphone. The survey found that 100% of participants followed the notifications about holding the smartphone with both hands at chest level while sitting upright. Xie et al. found that texting with both hands induced less muscle activity in upper trapezius muscles compared to texting with only one hand [41]. Sangyoung et al. found that upper trapezius muscles on both sides suffer fatigue when bending the neck, as the neck can bend up to 50 degrees [19]. This is related to the study of Choi et al., who found that splenius capitis and upper trapezius muscles are most fatigued when in a position with bending of the neck [21]. Dennerlein and Gustafsson discovered that using smartphones with head and neck positions in a tilting neck flexed posture to a neutral posture produced less muscle activity, thus resulting in less shoulder pain [22, 23].

Upper back pain in the “app use” condition was significantly lower than in the “no app use” condition at 15, 30, and 45 minutes. The survey found that 100% of participants followed the notifications about sitting upright. The most significant effect of good posture is its effect on the linkage of the spine with anterior pelvic tilting, which leads to a more “straight back posture” while sitting and reduces the force exerted on ligaments to induce less back pain [42].

Arm pain in the “app use” condition was significantly lower than in the “no app use” condition at 15, 30, and 45 minutes. The survey found that 100% of participants followed the notifications about holding the smartphone with both hands and relaxing the arms. This can be explained by the fact that this posture creates no arm strain, as the person is seated with arms in a relaxed position. Lee and Hong et al. found that holding the phone with both hands induced less muscle activity and increased pain thresholds in comparison to holding the phone with one hand [26, 27].

Hand pain in the “app use” condition was significantly lower than in the “no app use” condition at 15, 30, and 45 minutes. The survey found that 100% of participants followed the notifications about using the smartphone with both hands and relaxing the arms. Lee et al. found that using the smartphone with both hands induced less muscle activity and increased pain thresholds in the extensor and abductor pollicis muscles in comparison to holding the phone with one hand [26]. Related to this study, Hong et al. also found that texting with both hands resulted in less muscle activity in comparison to texting with one hand [27].

Taken together, the results of the current study clearly show that neck, shoulder, upper back, arm and hand pain in the “app use” condition was significantly lower than in the “no app use” condition. The survey found that 100% and 77.1% of the participants, respectively, followed instructions about frequent breaks and stretching muscles. Due to information and pop-up screen warnings in the application, this allowed smartphone users to take breaks and not remain in a sustained posture [35]. Sustained muscular contraction can cause sarcoplasmic reticulum tears, leaking calcium into ATP, resulting in muscle fibers contracting, flow of blood and oxygen to muscles reducing, and muscle discomfort [43] that can lead to muscle pain. Intolo et al. found that sitting in an upright position with frequent breaks and stretching muscles helps reduce muscle pain when compared to a sitting position [44]. The previous studies found that stretching muscles with frequent breaks helps prevent musculoskeletal disorders.

There was no significant difference in eye pain between the “app use” and “no app use” conditions. Participants followed the notifications about holding the smartphone farther away from the eyes at approximately 30-40 cm at 30 and 45 minutes, with intervals involving continuous blinking of the eyes. The results showed that 71.4% of the participants followed the instructions. The study may have been too short to generate any eye pain during the research. Pannate found that using a smartphone for a duration of more than 30 minutes is a clear cause of eye fatigue [11]. Related to the study of Beatriz et al., it was found that up-close viewing while using the smartphone for a long period of time can cause eye fatigue and blurry vision [11]. Kundart et al. found that while staring at the screen, blinking helps reduce causes of dryness of the eyes and eye strain [15].

Lower back pain did not show any difference between the “app use” and “no app use” conditions. This is due to the fact that participants were sitting with backrests supporting the iliac crest to the lumbar region. There was no significant difference between the two conditions. The survey found that 100% of participants followed the notifications about sitting upright. Morla and Bradl found that sitting with a backrest helps significantly reduce the curve of the lower spine and keep the lumbar spine in normal alignment compared to sitting without a backrest [45]. Claus and Scanell found that keeping the pelvis at an anterior pelvic tilt leads to a straighter back posture while sitting, helps reduce pressure on the spine and intervertebral disc, and lessens the force exerted on the ligaments [14]. In a well-seated posture, the lumbar regions are in neutral positions, which results in less load on the lumbar region and less muscle activity in the back extensor.

The observed effect size was 0.8, which was similar to the effect size of 0.9 observed in a previous experiment with children [39]. This effect size is clearly meaningful to the user, as it indicates that in the smartphone “app use” condition, pain was significantly less than in the “no app use” condition.

The main limitation of this study is that all participants used their smartphone without the app for one week, and then after that, they used their smartphone with the app for one week. There is some possibility that the observed decreases in pain observed in the study could be attributed to an unrelated time-varying cause such as a more relaxed attitude toward reporting pain during the second week. Therefore, in future studies, participants should be randomly assigned to “app use” and “no app use” groups.

5 Conclusion

Neck, shoulder, upper back, arm and hand pain in the smartphone “app use” condition were significantly lower than in the “no app use” condition at 15, 30, and 45 minutes in adult users aged 18-25 years old. We would recommend adult users to use the smartphone app to prevent risk of musculoskeletal pain during device usage.