Ergonomic arm support prototype device for smartphone users reduces neck and shoulder musculoskeletal loading and fatigue

Highlights

• Prolonged smartphone use without arm support can induce musculoskeletal fatigue and discomfort of neck and shoulder muscles.

• The ergonomic arm support prototype device decreased musculoskeletal loading and fatigue of neck and shoulder muscles.

• The ergonomic arm support prototype device reduced the risk of neck and shoulder MSDs for smartphone users.

Abstract

Smartphone use is a risk factor for both neck and shoulder musculoskeletal disorders. The objective of this study was to evaluate an ergonomic arm support prototype device, which may help improve posture while using a smartphone, by determining its effect on muscle activity, muscle fatigue, and neck and shoulder discomfort. Twenty-four healthy young adult smartphone users performed 20 min of smartphone game playing under two different conditions, smartphone use with support prototype device (i.e. intervention condition) and without (i.e. control condition), while neck and shoulder posture were controlled at 0° neck flexion and 30° shoulder flexion. Activity and fatigue of four muscles were measured using surface electromyography (sEMG), these were: anterior deltoid (AD), cervical erector spinae (CES), upper trapezius (UT) and lower trapezius (LT). The intervention condition showed significantly decreased activity of all muscles. Fatigue of all muscles, except LT, significantly increased over time compared to the start point in the control condition. There was no significant difference in muscle fatigue between each time point in the intervention condition. In conclusion, the ergonomic arm support prototype device can be used as ergonomic intervention to reduce neck and shoulder muscle loading and fatigue.

Introduction

The number of smartphone users is growing dramatically because of their various advantageous features. Smartphones are being used for communication, work, internet browsing and gaming. Thailand has 52.71 million smartphone users, representing 75.52% of the Thai population (Statista Research Department, 2020). Thai university students on average use their smartphone for 5.03 h per day (Namwongsa et al., 2018). Despite the advantages of using a smartphone, it can lead to increased risk of musculoskeletal disorders (MSDs), especially in the neck and shoulder regions (Kim, 2015; Xie et al., 2016). The prevalence of MSDs has been found to be associated with the pattern of smartphone use, including: session length of use >1 h, type of activities, multitasking (Toh et al., 2020) and total daily time spent (hours per day) using a smartphone (Berolo et al., 2011; Chu et al., 2011). Thai university student smartphone users reported the most commonly affected body areas to be the neck (32.5%) and shoulder (26.9%) (Namwongsa et al., 2018).

Awkward head and neck (flexion) postures during use are the main cause of MSDs from smartphone activities (Lee et al., 2015; Straker et al., 2009). The head and neck flexion angle and forward head shift distance are increased when using smartphones for long periods (Szeto et al., 2020), especially while texting (Guan et al., 2015; Lee et al., 2016; Xie et al., 2018) and walking (Han and Shin, 2019), compared with other uses. Smartphone users with neck pain have shown greater neck flexion angles than users without neck pain while using the smartphone (Kim, 2015). These results indicate that the flexed neck posture is a key problem and cause of neck pain in smartphone users. Smartphone use not only changes neck posture but also activates neck muscle loading. While using smartphones, subjects with neck pain have demonstrated more neck flexion, with increased cervical erector spinae (CES) and upper trapezius (UT) muscle activity than subjects without neck pain (Xie et al., 2016). Further, CES muscle activity was increased when the neck flexion angle increased during smartphone use (Namwongsa et al., 2019). From these results, the mechanism of neck MSDs is explained by increased cervical muscle activation against head weight and forces acting on the neck from awkward postures during smartphone use (Hansraj, 2014). The greater the neck flexion angle during smartphone use, the greater the risk of neck muscle fatigue and pain.

Smartphone use is not only a risk factor for neck musculoskeletal disorders, it is also a risk factor for shoulder musculoskeletal problems (Xie et al., 2016). A recent study reported that using a smartphone with appropriate neck posture induces compensation via shoulder muscle loading (Syamala et al., 2018). Although smartphone users corrected their neck posture appropriately following ergonomic recommendations in a previous study, participants reported they felt discomfort in both their shoulders and upper arms because they had to raise their upper arms to hold the smartphone close to improve vision (Namwongsa et al., 2019). This posture showed increased UT muscle activity, as UT is a shoulder stabilizing muscle, while the neck extensor muscles (CES) demonstrated lowest activation (Namwongsa et al., 2019). These results suggest that using a smartphone can cause shoulder musculoskeletal problems. To date, studies of the effect of smartphone use on shoulder biomechanics have not been extensively reported. Previous studies on kinematics of the upper extremity with other visual display unit (VDU) device use have demonstrated that shoulder flexion and elevation increased more when using a tablet on a desk than when using it on one's lap. When using a VDU device on a desk, neck extensor muscle activity (splenius capitis) was low, but shoulder flexor muscle activity (AD and UT) was high when the smartphone location was adjusted to a higher position (Chu et al., 2011; Jin et al., 2019; Penumudi et al., 2020; Young et al., 2013). Typing on a desktop computer without neck flexion, which requires greater shoulder flexion, increased LT muscle activity compared with smartphone texting in a flexed neck posture (Xie et al., 2016). These results demonstrate that prolonged smartphone use could induce musculoskeletal fatigue and discomfort of both neck and shoulder muscles.

To prevent neck and shoulder MSDs, supporting the forearm to keep the shoulder in a neutral posture is a recommended ergonomic posture (Cook et al., 2004; Delisle et al., 2006; Odell et al., 2007; Zhu and Shin, 2012) and it could be useful to reduce muscular loading and fatigue on the neck and shoulder. A recent study reported that forearm support had a significant effect on preventing upper limb disorders; forearm support reduced UT and AD muscle activity while the shoulder worked in a flexed position. Muscle activity was assessed in different shoulder flexion postures by Goncalves et al. (2017) when using a height adjustable table to support the subject's forearms.

Chair support (via armrest and backrest) has been shown in mobile phone users to reduce head and neck flexion angle, gravitational moment and muscle activity (Syamala et al., 2018). Although, using a height adjustable table or chair support is appropriate for computer or office work it is not convenient for smartphone users in various situations such as while sitting or standing in the subway or on public transportation, or when using it outside. If smartphone users had a portable support device, which could be used in various situations, it could have many benefits including the prevention of neck and shoulder MSDs.

The ergonomic arm support prototype device used in this study is a portable arm support device which two of the authors of this study (WT and RP) designed based on biomechanical principles (petty patent pending; Thailand patent application number 1903001634). The design principle is that it allows the user to rest their arm on the device. Therefore, the whole arm weight is transferred to the device which could reduce gravitational moment of the upper extremities resulting in decreased neck and shoulder muscle loading. The force from the device is continuously conveyed to the user's waist and hip which is the broadest part of a user's body. The prototype device was designed to attach to the user's body so it could be easily carried for use anywhere; this feature distinguishes it from other stationary arm supports.

Previous studies reported that smartphone use in the 0° neck flexion posture requires contraction of the shoulder flexor muscles (AD) and elevator muscles (UT) to generate shoulder flexor and elevator moment to counteract the gravitational force acting on the arm (Chiu et al., 2015; Jin et al., 2019; Young et al., 2013). When using a smartphone with the arm support device, shoulder flexor and elevator moment may be decreased by force transferred to the device, in addition to consequent decreases in shoulder flexor (AD) and elevator (UT) muscle activity. The purpose of this study was to evaluate the effect of an ergonomic arm support prototype device on muscle activity during smartphone use to determine muscle fatigue and discomfort in the neck and shoulders.