A study of musculoskeletal loading in using a touchscreen smartphone among young people with and without chronic neck-shoulder pain

Abstract

An upward increase in the use of touchscreen smartphones in recent years has given rise to a growing concern about its impact on the musculoskeletal health. This study was to investigate the patterns of muscle recruitment and spinal kinematics between young people with and without chronic neck-shoulder pain when they performed smartphone texting and computer typing. Twenty healthy young adults (mean age=24.6±3.1) and 20 with chronic neck-shoulder pain (mean age=23.2±3.1) were recruited and allocated to Case Group and Control Group, respectively. All subjects were required to perform three tasks, namely: 1) texting on a touchscreen smartphone with both hands ("bilateral texting"), 2) texting with one hand ("unilateral texting"); 3) typing on a desktop computer ("computer typing"). Each task was performed for 10 minutes and the order of tasks was randomized and balanced. During these tasks, surface electromyography was recorded bilaterally from three proximal postural muscles (cervical erector spinae "CES", upper trapezius "UT" and lower trapezius "LT") as well as bilaterally from four distal hand/thumb muscles (extensor carpi radialis "ECR", extensor digitorum "ED", flexor digitorum superficialis "FDS" and abductor pollicis brevis "APB"). The static (10th %ile), median (50th %ile) and peak (90th %ile) activity were computed for each muscle and compared among the three tasks. Meanwhile, median angular displacements and ranges of joint angles were examined in the cervical, thoracic and lumbar regions from three anatomical planes, namely sagittal (flexion/extension), frontal (left/right side flexion) and transverse (left/right rotation) planes. Subjects were also asked to rate their discomfort intensities using numeric rating scale (0-10) and overall fatigue using rate of perceived exertion (RPE) (6-20) after each task. In addition, correlations among muscle activity, kinematics and discomfort scores were examined. Compared with Control Group, Case Group showed consistently higher activity in bilateral CES and UT while performing the three tasks and this pattern was most prominent for right-sided UT. Case Group also spent more time with a slightly higher angle in thoracic flexion than Control Group during bilateral texting and computer typing. Furthermore, Case Group displayed increased cervical side flexion to the right during smartphone texting and significantly greater ranges in the cervical rotation during performing the three tasks compared with Control Group. Regarding the subjective discomfort, the change of summed discomfort scores and RPE scores were significantly higher in Case Group compared with Control Group after the all tasks. There were no clear patterns of association among muscle activity, kinematics and subjective discomfort. Generally, unilateral texting was associated with higher activity in right-sided distal muscles, a greater right side rotation angle, a smaller neck flexion angle and greater ranges in cervical rotation and side flexion compared with bilateral texting. Compared with computer typing, smartphone texting was associated with higher activity in CES and APB, lower activity in UT, LT, ECR and ED, greater joint angles in the cervical and thoracic flexion and smaller ranges of movements in cervical flexion/extension and rotation. In conclusion, this study demonstrated that young adults with chronic neck-shoulder pain consistently displayed altered motor control patterns while performing smartphone texting and computer typing. Smartphone texting was associated with increased cervical and thoracic flexion angles and a relatively static cervical posture. Compared with texting on a smartphone with one hand, texting with both hands seemed more preferable if users could maintain an upright and neutral spine.