Occupational cranking operations: The scapula perspective. (February 2019)

• Record Type: Journal Article
• Authors: Lin, Jia-Hua; Xu, Xu
• Is Part Of: Applied ergonomics. Volume 75(2019)
• Page Start: 129
• Page End: 133
• Publication Date: 2019-02
• Subjects: Shoulders -- Trucking -- Musculoskeletal disorders -- Best practice; Human engineering -- Periodicals; 620.82
• DOI: 10.1016/j.apergo.2018.09.011
• Languages: English
• ISSNs: 0003-6870

Abstract

Abstract: Cranking the landing gear is a common task performed by truck drivers to raise or lower trailers. This task poses a risk to the shoulder joint due to the required forceful exertion and the posture constrained to the hand-handle interface. As a potential occupational risk, there has been no definitive guideline for best practices among truck drivers. An operator can crank perpendicular (frontal) or parallel (sagittal) to the crank rotation. In this laboratory study, the effects of cranking method and resistance on scapular range of motion and shoulder muscle activity were observed in 12 participants. Scapular posture was measured using an optical motion tracking system. EMG was monitored on 16 muscles contributing to shoulder movement. The results show that during frontal cranking, the scapular range of protraction was 28 ± 11.6°, which was more than the sagittal cranking (23 ± 10.4°), indicating a decreased subacromial space and elevated shoulder impingement risk. Seven muscles (all three deltoid muscles, middle trapezius, supraspinatus, infraspinatus, and teres minor) demonstrated that when the crank resistance was low, the front cranking method resulted in lower activity than the side cranking. When the crank resistance was 20 Nm, the muscle activity on these seven muscles was greater when cranking from the front than from the side. Based on these observations, we suggest that when the resistance is low (lowering the trailer) the driver should stand facing the trailer. On the contrary, it is advantageous to stand parallel to the trailer and crank while raising the trailer to apply the full body strength to reduce the shoulder load. Highlights: Shoulder postures and muscle activity were measured in this laboratory study with sagittal and frontal cranking postures. Frontal cranking resulted in lower shoulder muscle activity than sagittal cranking when there was no cranking load. When lowering the trailer (low resistance), the driver should stand facing the trailer and crank the handle frontally. While raising the trailer, it is better to crank sagittally to use full body strength to reduce the shoulder load.