Ergonomic evaluation of upper extremities muscle activity pattern during 60-min smartphone texting

Abstract

BACKGROUND: Smartphone usage has increased rapidly in the last decade due to rapid technological advancements. This extensive usage of smartphones led to physiological problems and musculoskeletal disorders (MSD) due to inappropriate postures. OBJECTIVE: Past studies have reported the effects/discomfort of smartphone usage for short periods, ranging from 3–20 min, which does not represent the current era of smartphone dependency (approximately 7-hr/day). METHODS: This study was performed on fifty-four participants aged 20–28 with 1-hr smartphone texting in a sitting posture. Flexion angles, both sides (dominant and non-dominant) muscle activity (maximum voluntary contraction %) at sternocleidomastoid (SCM), upper-trapezius (TRP), extensor digitorum (EDM) and abductor pollicis brevis (APB) muscles, and subjective discomfort were analyzed. RESULTS: After 1-hr smartphone texting, the muscle activity at eight upper extremities: SCM (24.80%), TRP (29.45%), EDM (14.44%) and APB (19.87%) significantly (p <  0.001) increased by 1.5–1.9 times with 27.4±3.18° and 82.94±7.03° head and lower-arm flexion angles, respectively. The mechanical loads on the cervical spine increased by 4.6 times, and subjective discomfort by 3 times. CONCLUSION: Maintaining the same posture for a long duration causes postural stress, muscular imbalances, and discomfort, leading to MSD with increased cervical intervertebral disc pressure.