Fatigue during prolonged intermittent overhead work: reliability of measures and effects of working height

Shoulder pain is prevalent among industrial workers and existing evidence supports that overhead work is an important specific risk factor. Existing guidelines are limited, with overhead work typically recommended to be avoided, and research on overhead work has been mixed in terms of the effects of increasing arm reach. A laboratory-based simulation of overhead work was conducted, at three working heights, in order to facilitate improved guidelines and to identify potential non-linear effects of overhead work height. Several indicators of shoulder fatigue served as outcome measures and a preliminary study was performed to assess the reliability of several of these measures. Fatigue measures based on electromyography (EMG) generally had low reliability, whereas excellent reliability was exhibited for ratings of perceived discomfort (RPD). Consistent with this, no effects of overhead work height were found on EMG-based measures, yet clear non-linear effects were found on RPD and task performance. The source of the effects of work height appeared to be related to a combination of muscle activation levels and demands on precision/control at the highest location. These results support the utility of subjective measures for relatively low-level intermittent exertions and demonstrate increasingly detrimental fatigue and performance effects at extremes in reach during overhead work.     

Comparing standing posture and use of a sit-stand stool: Analysis of vascular,muscular and discomfort outcomes during simulated industrial work

Sit-stand stools are available for use in industrial settings, but there is a lack of quantitative evidence demonstrating benefits for lower limb, back and/or neck/shoulder outcomes. In this paper we describe an experiment conducted to compare and contrast posture and time-related differences in muscular and vascular outcomes during 34 min of manual repetitive work performed in either standing or sit-standing work posture. We measured vascular parameters in the lower limbs, and muscular parameters in the trunk and neck/shoulder, and discomfort in the three regions as participants accomplished a repetitive box-folding task. Results show that blood flow in the foot (p = 0.022) and ankle mean arterial pressure (p < 0.001) were greater during standing. Left gluteus medius and external oblique activation was higher during standing, while sit-standing work resulted in higher levels of co-activation between the left erector spinae and external oblique muscle pair (p = 0.026). Neck/shoulder muscle activity was not significantly different between the conditions. Reported discomfort did not differ significantly for the trunk and neck/shoulder region, but standing resulted in higher level of reported discomfort in the lower limb. The sit-stand posture used in this experiment appears to prevent the undesirable lower limb outcomes associated with static standing work posture.Relevance to industryThis work demonstrates quantitative evidence to support the potential use of a sit-stand stool for industrial work operations, at least over relatively short durations.     

Effect of working position and cold environment on muscle activation level and fatigue in the upper limb during manual work tasks

Several occupational groups are exposed to periods of low ambient temperatures while performing manual work tasks outdoors. Work tasks typically include heavy lifting, tool handling, and overhead work. This study evaluated the effect of working position and cold environment on muscle activation level (%RMS_max) and fatigue in the upper limb during manual work tasks. Fourteen male participants (25 ± 3 years, 80.9 ± 6.4 kg, 182 ± 5 cm) completed a 2-h test protocol consisting of five test periods alternating with four work periods, wearing identical sets of clothing, under cold (−15 °C) and control (5 °C) conditions. The work periods consisted of manual work at the hip level, manual overhead work, and a lifting exercise. The test periods consisted of isometric maximal voluntary contractions (MVC) and seated rest. Skin temperatures decreased during cold exposure, especially in the extremities. %RMS_max in the forearm was higher in the cold condition both during overhead work and work at the hip level than that for the same work in the control condition, especially at the end of the test when the difference was approximately 25% (equating to 2–3 %RMS_max). For the middle deltoid muscle, the %RMS_max was approximately three times (or 10 %RMS_max) higher during overhead work than work at the hip level, but there was no additional cost of working in the cold. Signs of deltoid muscle fatigue (decrease in electromyography median power frequency and an increase in %RMS_max) were observed during the overhead work periods in both temperature conditions. No decrease in MVC, as a sign of overall muscle fatigue, was observed in either condition.Relevance to industryThis study demonstrated that when wearing suitable cold-weather protective clothing, the adverse effect of work posture is much higher than that of cold on muscle demand and physical strain.