Effects of overhead work involving different heights and distances on neck and shoulder muscle activity.

Background: Although overhead work is closely related to musculoskeletal disorders, it is difficult to avoid these postures in daily working conditions. In industrial tasks that require elevated arm postures above shoulder height, flexibility in the location of the task is necessary.

Objective: This study investigated the sternocleidomastoid, upper trapezius, lower trapezius, and anterior deltoid, serratus anterior muscle activities during overhead work involving four different height and distance locations performed by healthy adult participants.

Methods: Eighteen young male right-hand-dominant workers were recruited. The right upper trapezius, lower trapezius, serratus anterior, anterior deltoid, and sternocleidomastoid muscle activities were measured under for overhead work condition (Location 1: overhead work with a height of 10 cm above the head of each subject and distance of 15 cm, Location 2: overhead work with a height of 10 cm above the head of each subject and distance of 30 cm, Location 3: overhead work with a height of 20 cm above the head of each subject and distance of 15 cm, Location 4: overhead work with a height of 20 cm above the head of each subject and distance of 30 cm).

Results: In Location 3, there was significantly higher neck extension range of motion compared to Location 1, Location 2 and Location 4. In Location 1, the activities of the upper trapezius, lower trapezius, serratus anterior, anterior deltoid, and sternocleidomastoid muscles were significantly lower than those in Location 3 (p<0.05). In Location 2, the activities of the upper trapezius, lower trapezius, serratus anterior, anterior deltoid, and sternocleidomastoid muscles were significantly lower than those in Location 4 (p<0.05). In Location 1, there were significantly lower upper trapezius, lower trapezius, serratus anterior, and anterior deltoid muscle activities than in Location 2 (p<0.05). In Location 3, there were significantly lower upper trapezius, lower trapezius, serratus anterior, and anterior deltoid muscle activities than in Location 4 (p<0.05). In Location 1, there was significantly higher sternocleidomastoid muscle activity than in Location 2 (p<0.05). Finally, In Location 3, there was significantly higher sternocleidomastoid muscle activity than in Location 4 (p<0.05).

Conclusions: Overhead workers should engage in work that involves a low height and near distance. Height appears to be a stronger risk factor than distance in overhead work.