Neck muscles activity and upper body extremity angles in dynamic overhead lifting

Abstract

Injuries of the neck and shoulders are common among workers who perform overhead tasks. In order to develop an injury-free working environment with regards to occupational musculoskeletal stress, it is pivotal to understand the pathophysiology of mechanical stress on the musculoskeletal system. The objective of this research was to study the effect of overhead lifting on the sternocleidomastoid and upper Trapezius muscles. Upper body joint angles were also analyzed using APAS during the overhead lifting. This study was conducted using two devices. The set of equipment incorporates an electromyography device, and the APAS. Two electrodes were placed at the muscle belly of the sternocleidomastoid and the upper Trapezius muscles to record the muscle activity. Each participant was asked to lift 15%, 30% and 45% of his/her MVC, The MVC was determined by a non dynamic lifting task. ANOVA was performed to test the effect of different loads on the muscle activity. Correlation analysis was performed to observe the effect of increasing the lifted weight on the joint angles of the upper body extremities. Results of this research show a strong relationship between neck muscle activities and overhead lifting. The level of sternocleidomastoid activity increased 11.8% from a 15% MVC load to a 30% MVC load and increased 16.53% from a 30%MVC to a 45% MVC. All these values were statistically significant. At the trapezius: a 10.64% increase from 15% MVC to 30% MVC, and a 7.76 % increase from 30% MVC to 45% MVC. The significance level of alpha = 0.05 reveals that weight increase has a significant effect on the MAV EMG of the neck muscles. A slight increase in the elbow joint angle of 0.1% was recorded from 15% MVC to 30% MVC. A 2.88% increase in elbow joint angle was recorded from 30% MVC to 45% MVC, with an overall 2.98% increase from 15% MVC to 45% MVC. There was no effect of changing elbow angles on the sternocleidomastoid muscle. On the other hand, flexion of the shoulder angle in the sagital plane had a significant effect on both the Trapezius and the sternocleidomastoid muscles.