Why You Should Use Armrests and Back Support During Cellphone Use

Steelcase Gesture vs Leap Comfort

An interesting study 1 published in ‘Applied Ergonomics’ looked at neck and shoulder stress during cellphone use. The study concluded that people using cellphones should use armrests as well as have proper back support.

Why was this Study Conducted?

We all know that mobile phones are being used all around the world. Due to their versatility (covering academia, professional life, and leisure), the time spent on mobile phones continues to increase. According to data, almost 77% of the US population use their cellphones for 3-4 hours a day. While useful, such a device is also accompanied by certain side effects.

The risk of musculoskeletal injury and pain, especially in the upper extremities, is present because of mobile phone use. Previous studies have shared that prolonged neck flexion is linked to cellphone use, and this can increase the risk of a person experiencing neck pain. Using cellphones can also increase the risk of developing musculoskeletal pain in the fingers and wrists due to repetitive movements of the hands and awkward postures.

Offering support through armrests could be useful when it comes to alleviating physical demands experienced by the upper extremities. However, more research is required to systematically evaluate the efficacy of adequate ergonomic controls to aid with the decrease of biomechanical exposures when a person uses a cellphone while sitting.

The objective of this study was to quantify the kinematics of the head and neck, gravitational moment as well as the muscle activity in the neck when a cellphone is being used. It also set out to evaluate the effects of armrests and back support on biomechanical measures.

What was the Methodology?

This study had 20 young adults as participants. Their average age was 23 years old. The participants were equally distributed by sex. All of them had been using cellphones for around 6-7 years. None of them had any musculoskeletal pain in the past 7 days. They also didn’t have a history of musculoskeletal disorders in their neck and upper extremities. 

The participants were asked to use their cellphones under a total of eight different experimental conditions. Said conditions included 4 different cellphone positions and 2 different chair supports. The cellphone locations included chest, eye, lap, and a self-selected position. The chair support conditions were armrests and back support and no support.

The gaze distance (between the cellphone and eyes) was self-selected for each condition.

Take note; during each task, the participants accepted a series of standardized, general open-ended questions. They answered the questions via text for 5 minutes. Residual fatigue effects were reduced by giving participants 5-minute breaks between the texting sessions.

  • Kinematic Data

Kinematic data from the person’s head and neck were sampled at 100 Hz using an 8-camera optical motion capture system with reflective markers during the texting sessions.

The head, neck, craniocervical angle, gravitational moment, and gravitational moment-arms on the neck were calculated using a custom-built Matlab program.

  • Electromyography

Using Ag/AgCL surface electrodes and a wireless logger, TRAP (upper trapezius) and SPL (splenius capitis) muscle activities were bilaterally measured at a sampling rate of 1000 Hz.

What were the Results?

According to the collected results, a person’s neck flexion, head flexion, and craniocervical angles were significantly different depending on the phone position and chair support. The results showed that the eye (phone position) and chair supports showed the lowest neck flexion and head flexion angles, and the highest craniocervical angle. 

Furthermore, the Lap phone position without any chair support showed the highest neck flexion and head flexion angles, and the lowest craniocervical angle. There were also significant interactions between the phone position and the chair support in the neck flexion angle, head flexion angle, and craniocervical angle.

Depending on the chair support and phone position, the gravitational moment at C7-T1 varied significantly. Also, the Eye (phone position) and chair support showed the lowest gravitational moment. The Lap (phone position) without any chair support showed the most significant gravitational moment.

There were also significant interactions between phone positions and chair support on the gravitational moment.

  • Electromyography (EMG)

The results showed significant differences between phone position and chair support in muscle activity in the TRAP) and SPL.

Talking about TRAP, the Lap (phone position) and chair support showed the lowest muscle activities. The Eye (phone position) without chair support showed the highest muscle activities. 

For SPL, the Eye (phone position) and chair support showed the lowest muscle activities, while Lap (phone position) without chair support showed the highest muscle activities. Also, interactions between phone position and chair support were significant in TRAP.

What was Concluded?

The current study evaluated if there were any differences in a person’s head/neck flexion angle, the neck’s gravitational moment, and muscle activity in the neck/shoulder depending on the position of the phone (chest, eye, lap, and self-selected) and chair support (support and no support) when a cellphone is being used. 

The results showed that gravitational moment, flexion angle, and muscle activity in the neck and head of a person were significantly impacted by both factors.

This laboratory-based study indicated that using cellphones may lead to an increase in the risks for musculoskeletal pain and injuries in a person’s neck and shoulder regions. The increase in said risks is due to the rise in muscle activities, neck/ head flexion, and gravitational moment. 

The current results suggested that placing a cellphone at eye level while having adequate body support can aid with the reduction of biomechanical stresses in a person’s neck and upper extremities.

More research should be conducted to help people understand proper postures when using their cellphones to help address issues of pain and discomfort.

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