How do different standing positions affect trunk muscle activation in LBP-developers during prolonged standing?

Abstract

Background: Low back pain developers (PDs) are individuals at a high risk of developing low back pain (LBP), especially during prolonged standing. Understanding their characteristics is essential for devising effective preventive strategies. Prolonged standing has been associated with increased co-contraction of trunk muscles and elevated activity of the trunk extensor muscles. This study aims to examine the effects of using a normalized footrest height and altering arm positions on muscle activity in PDs.

Methods: Twenty-four female PDs, identified by a > 10 mm increase on the visual analog scale (VAS) during prolonged standing, were recruited. They were randomly divided into two groups: Group A used a footrest intermittently, while Group B used a footrest combined with changes in arm positions (shoulder flexion and hands crossed on the clavicles). Muscle activity was monitored using electromyography (EMG) over a one-hour standing protocol.

Results: Both interventions significantly reduced lumbar erector spinae (LES) muscle activity, as well as co-contraction of the trunk flexor and extensor muscles (p < 0.05). The group that adjusted their arm positions (Group B) experienced a greater reduction in muscle activity (p = 0.05). Additionally, transversus abdominis (TrA) muscle activity slightly increased in both groups, with a more notable increase in Group B (p > 0.05). Although lumbar spine muscle activity decreased, thoracic spine extensor (TES) activity increased in Group B. This increase is attributed to the engagement of the thoracic spine during upper limb movement, compensating for the reduced lumbar muscle activity, which may help alleviate back pain.

Conclusions: Using footrests cyclically and adjusting arm positions can help prevent back pain during prolonged standing by promoting muscle relaxation, reducing fatigue, and improving posture. These findings offer practical strategies for enhancing workplace ergonomics, particularly for occupations involving prolonged standing.

Trial registration: This study is registered in the Clinical Trial Registry ( http://www.irct.ir/ ) with Trial ID 71,648 and IRCT ID IRCT20230628058610N1, dated January 20, 2024.