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3 International Journal of Occupational Medicine and Environmental Health

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Shoulder girdle muscle activity and fatigue during automobile chassis repair

100%

Tian B. , Yu S. , Chu J. , Li W.

International Journal of Occupational Medicine and Environmental Health

2019

tom 32

nr 4

537-552

Objectives The objective of this study was to assess the postures that were commonly used in automobile chassis repair operations, and to evaluate shoulder girdle muscle fatigue for different combinations of the weight of hand-tools. Material and Methods Two right muscles, including upper trapezius (UT) and middle deltoid (MD), were selected. Surface electromyography (SEMG) and a perceived level of discomfort (PLD) were used to assess the degree of shoulder girdle fatigue. Fifteen healthy young male subjects from the Northwestern Polytechnical University participated in the test. The test consisted of assuming 4 different postures and maintaining each of them for 60 s. The 4 postures varied in terms of dumbbell weights, standing for the hand-tools weight: W1 was 0.48 kg and W2 was 0.75 kg; the 4 shoulder postures were shoulder flexions of 150°, 120°, 90°, and 60°, combined with an included elbow angle of 180°, 150°, 120° and 90°, respectively. The experimental sequences were randomly selected. The signals of SEMG and the values of PLD in the shoulder girdle were recorded in 60 s. All subjects completed the whole test. The repeated measure analysis of variance (ANOVA) was performed to ascertain differences between dumbbell weight (0.48 kg and 0.75 kg) and shoulder postures (150°/180°, 120°/150°, 90°/120° and 60°/90°). The Friedman test was utilized to determine the significant differences for UT(PLD) and MD(PLD) on shoulder postures. Spearman’s correlation was used to analyze the relationship between the subjective and objective measurements. Results Significant correlational relationships existed between the UT percentage of the maximal voluntary electrical activation (%MVE) and UT(PLD) (r = 0.459, p < 0.01), between MD(%MVE) and MD(PLD) (r = 0.821, p < 0.01). The results showed that SEMG and PLD of the 4 postures under analysis differed significantly (p < 0.05). Conclusions It was indicated that posture T4 (shoulder forward flexion 60° and included elbow angle 90°) resulted in the lowest fatigue, both in terms of the objective measure and the subjective perception, which meant that this posture was more ergonomic. Int J Occup Med Environ Health. 2019;32(4):537–52

Effect of airplane passenger seat armrest height on human neck comfort when using a smartphone

75%

Tang X. , Yu S. , Chu J. , Zhang L. , Fan H. , Hu Y. , Jiang G.

International Journal of Occupational Medicine and Environmental Health

2021

tom 35

nr 2

199-208

ObjectivesThe objective of this study was to explore the relationship between seat armrest height and human neck comfort when using a smartphone while sitting on a passenger seat during the flight.Material and MethodsThe authors used a wireless angle-measuring instrument and subjective comfort scale to evaluate the changes of head flexion angle and neck comfort level of 24 young smartphone users in an aircraft simulated cabin.ResultsThe study results indicated that using a smartphone while sitting on a passenger seat during the flight would pose a larger discomfort to the neck, and the discomfort would be higher for gaming than reading tasks. Seat armrest height is related to the comfort level of the neck when using a smartphone, increasing the height of the armrest can effectively alleviate discomfort in this state.ConclusionsConsidering the prevalence of passengers using smartphones in aircraft, a seat armrest that can be properly adjusted in height, which can effectively reduce the risk of passenger head flexion angle and neck discomfort.

The effects of the seat cushion contour and the sitting posture on surface pressure distribution and comfort during seated work

75%

Li W. , Mo R. , Yu S. , Chu J. , Hu Y. , Wang L.

International Journal of Occupational Medicine and Environmental Health

2020

tom 33

nr 5

675-689

ObjectivesThe purpose of this paper is to investigate the effects of the seat cushion contour and the sitting posture on the seat pan interface pressure distribution and subjective comfort perception.Material and MethodsOverall, 16 volunteers typed a text passage on a laptop while seated, by assuming 3 kinds of common sitting postures (forward, relaxed and upright) in 4 seat cushion configurations: chair only, and chair with 1 of 3 supplementary cushions. Pressure data and cushion comfort ratings were collected in the experiment.ResultsIt was found that the sitting posture and the seat cushion contour had different impacts on surface pressure. The seat cushion contour had an impact on pressure parameters and pressure distribution on the seat pan, while the sitting posture affected the location of peak pressure on the seat pan. The correlation analysis revealed that the subjective comfort rating was significantly correlated with average pressure (AP) and mean peak pressure (MPP).ConclusionsThe conclusion was that the cushion contour had a greater effect on seat pan interface pressure parameters than the sitting posture. Notably, AP and MPP can be indicators for assessing seat cushion comfort in a short-term perspective.