Shoulder muscle loading and task performance for overhead work on ladders versus Mobile Elevated Work Platforms

A high incidence of Musculoskeletal Disorders (MSDs) has been reported in the construction sector. The use of ladders in the workplace has long been identified as a significant risk that can lead to workplace accidents. However, it is unclear if platform types have an effect on the physical risk factors for MSDs in overhead work. The aim of this study is to perform a pilot study on the effects of hand activity on both shoulder muscle loading and task performance while working on ladders versus Mobile Elevated Working Platforms (MEWPs). It is hypothesised that work on ladders would result in greater muscle loading demands, increased levels of discomfort, and reduced performance due to the restrictions on postures that could be adopted. A field study (n = 19) of experienced electricians on a construction site found that workers spent approximately 28% of their working time on ladders versus 6% on MEWPs. However, the durations of individual tasks were higher on MEWPs (153 s) than on ladders (73 s). Additionally, maximum levels of perceived discomfort (on a VAS 0–100) were reported for the shoulders (27), neck (23), and lower regions of the body (22). A simulated study (n = 12) found that task performance and discomfort were not significantly different between platform types (ladder vs. MEWP) when completing either of three tasks: cabling, assembly and drilling. However, platform and task had significant effects (p < 0.05) on median electromyographic (EMG) activity of the anterior deltoid and upper trapezius. EMG amplitudes were higher for the deltoid than the upper trapezius. For the deltoid, the peak amplitudes were, on average, higher for ladder work over MEWP work for the hand intensive cabling (32 vs. 27% Maximal Voluntary Exertion (MVE)) and the assembly task (19 vs. 6% MVE). Conversely, for drilling, the peak EMG amplitudes were marginally lower for ladder compared to the MEWP (3.9 vs. 5.1% MVE). The general implication was that working on the MEWP involved lower shoulder muscle loading for cabling and assembly task. A difference due to platform type was not present for drilling work.     

An evaluation of arborist handsaws

A review of the scientific literature reveals little research on the ergonomics of handsaws and no literature on the specific challenges of arborist saws (saws for cutting and pruning living trees). This study was designed to provide some insight into the effects of saw design and height of sawing activity on the biomechanical response of the upper extremity. Eighteen participants performed a simple sawing task at three different heights using six different arborist handsaws. As they performed this task, the electromyographic activity of several muscle groups of the forearm (flexor and extensor digitorum), arm (biceps brachii long and short heads) and shoulder girdle (posterior deltoid, infraspinatus and latissimus dorsi) were sampled. Also gathered were the wrist postures in the radial/ulnar plane at the beginning and ending of the sawing stroke, the time to complete the sawing task and a subjective ranking of the six different saws. The results show an interesting mix of biomechanical and subjective responses that provide insight into handsaw design. First, there were tradeoffs among muscle groups as a function of work height. As work height increased the biceps muscles increased their activation levels (∼19%) while the posterior deltoid activity decreased (∼17%) with the higher location. The results also showed the benefits of a bent handle design (average 21% reduction in ulnar deviation). The subjective responses of the participants generally supported the productivity data, with the saws demonstrating the shortest task completion time also being the ones most highly ranked.

Relevance to Industry

Understanding the stresses placed on the upper extremity during sawing activities, and design features that can reduce these stresses, may help saw designers to create products that reduce the risk of injury in workers who use handsaws.     

The effects of shoulder posture on neck and shoulder musculoskeletal loading and discomfort during smartphone usage

While using their smartphone, users tend to adopt awkward neck and shoulder postures for an extended duration. Such postures impose the risk of MSDs on those body parts. Numerous studies have been undertaken to examine neck posture; however, few studies have investigated shoulder postures. This study examined various shoulder postures during smartphone use and their effect on neck and shoulder kinematics, muscle loading, and neck/shoulder discomfort. Thirty-two asymptomatic young adult smartphone users randomly performed texting tasks for 3 min at four different shoulder flexion angles (15°, 30°, 45°, and 60°), while maintained a neck posture in the neutral position (0° neck flexion angle). Measures were taken of neck and shoulder muscle activity of the cervical erector spinae (CES), anterior deltoid (AD), upper trapezius (UT) and lower trapezius (LT), and kinematic data (angle, distance and gravitational moment). Results showed AD and LT muscle activity significantly increased when the shoulder flexion angle increased with an opposite effect on CES and UT. A recommended shoulder posture was identified as 30° flexion, as this yielded the best compromise between activation levels of the four muscles studied. This angle also induced the lowest neck/shoulder discomfort score. The findings suggest smartphone users hold their device at approximately 30° shoulder flexion angle with their neck in a neutral posture to reduce the risk of shoulder and neck musculoskeletal disorders when smartphone texting.Relevance to industrySmartphone use in the manufacturing and service industries is an integral part of work and useful means of communication tool. Awkward postures during extensive smartphone use impose an increased risk of both neck and shoulder musculoskeletal disorders. Shoulder flexion angles need consideration when making recommendations about safe work postures during smartphone use.     

Segment characteristics and severity of head-on crashes on two-lane rural highways in Maine

More than two out of three of all fatal crashes in Maine occur on rural, two-lane collector or arterial roads. Head-on crashes on these roads account for less than 5% of the crashes, but they are responsible for almost half of all fatalities. Data analyzed in this study was provided by Maine Department of Transportation and covers all head-on crashes for 2000-2002 during which period there were 3,136 head-on crashes reported. Out of these, 127 were fatal crashes and 235 produced incapacitating but not fatal injuries. These two categories made up over 75% of the crash cost. A clear majority of head-on crashes on two-lane, rural roads in Maine were caused by drivers making errors or misjudging situations. Illegal/unsafe speed was a factor in 32% of the crashes while driver inattention/distraction was a primary factor in 28%. Fatigue was responsible for around one in 40 crashes and one in 12 fatal crashes. Alcohol or drugs was a factor in one in 12 crashes and one in nine fatal head-on crashes. Less than 8% of fatalities involved someone overtaking another vehicle, and only around 14% involved a driver intentionally crossing the centerline. Two in three fatal head-on crashes occurred on straight segments and 67% of these happened on dry pavement. There is a clear trend towards higher speed limits leading to a higher percentage of crashes becoming fatal or having incapacitating injuries. There is also a clear trend - if one keeps speeds constant and AADT within a certain range - that wider shoulders give higher crash severities. Also, for higher-speed roads, more travel lanes (than two) increase crash severity. In summary, there seems to be two major reasons why people get across the centerline and have head-on collisions: (a) people are going too fast for the roadway conditions; or (b) people are inattentive and get across the centerline more or less without noticing it. The latter category of crashes could probably be reduced if centerline rumble-strips were installed. More or less all head-on collisions could be eliminated if median barriers were installed. In-vehicle technology could also be used to significantly reduce the incidence of lane departures. Furthermore, today's speed limits should be better enforced since a high percentage of serious crashes involve illegal speeding. This should be combined with lowered speed limits for targeted high-crash segments.     

Testing of a workstation efficiency evaluator tool

This paper presents three studies that test and characterize input errors and their impact on selected outputs of a method and tool to predict shoulder loading and work element time from seated, light assembly workstation layout. Studies examine the impact of 1) different hand loads on shoulder load prediction, 2) potential tool user hand location measurement errors, and 3) tool response to simulated hand location input error. The results of the first study found that predicted shoulder load in response to hand loads from newly created, load specific shoulder load models differed from the original method's base models by an average of 5%–12% within the first 100 g of hand loading and 150%–210% for 1000 g hand loads, depending on the population percentile being predicted. In the second study, average hand location measurement error of participants was within 1 cm of the desired referent value measured from either a virtual or physical workstation. Results in study three showed that the impact of simulated hand location measurement error on average shoulder load and movement time prediction was low (<0.05 Nm and <3.6 ms) and demonstrated the potential to cancel out individual task error over a number of work tasks. Combining the user input error results with the simulated error outputs demonstrated that the impact of human error is relatively low. Within parameters similar to these studies the tool should work well in the design-stage assessment of seated, light assembly workstations.Relevance to industryThis testing of a tool for predicting task time and shoulder loading from layout information in the design-stage of seated, light assembly workstations has shown acceptable performance for light assembly hand loads up to 100 g with an anticipated input error under 1 cm and low output errors for estimated shoulder load and movement time.     

Neck and shoulder muscle activity among ophthalmologists during routine clinical examinations

Muscular demands during common clinical ophthalmologic activities may contribute to the high prevalence of musculoskeletal health outcomes observed among ophthalmologists and other eye care physicians. Characterizations of the muscle activation patterns in the live ophthalmologic environment are lacking. This study was conducted to (i) characterize the frequencies and durations of common activities performed by ophthalmologists during routine clinical examinations, (ii) characterize neck and shoulder muscle activation patterns during the whole clinical work day, and (iii) explore differences in neck and shoulder muscle activation patterns between common clinical activities. Fifteen ophthalmologists performed routine patient examinations in an outpatient ophthalmology clinic while continuous surface electromyography measurements of the upper trapezius and anterior deltoid muscles were obtained. Results indicated that while computer use was the most frequently performed clinical activity, use of the indirect ophthalmoscope, followed by use of the slit lamp biomicroscope, required greater muscular demands than computer use or other clinical activities. Results provide evidence that the clinical activities of indirect ophthalmoscope and slit lamp biomicroscope use are appropriate for ergonomic intervention.     

The relationship between charge shape characteristics and fill level and lifter height for a SAG mill

A predictive model that allows mill fill level and the lifter height to be determined from measurements of the head, bulk and impact toe positions for a generic SAG mill has been developed using data from a series of three dimension DEM simulations. A Design of Experiment (DOE) approach is used to define a series simulation conditions with the two factors being the lifter height and the fill level. The charge structure is characterised by the locations of the head, shoulder, bulk toe and impact toe. These are determined by visual analysis of the particle trajectories. The spatial variation of the liner pressure distribution can provide valuable information on the structure of the charge. This was found to vary systematically with lifter height and fill level. The relationships between the visual key locations and the key features of the pressure distributions were identified and found to be well described by linear equations. Finally, parametric models are fitted to the DEM data for both the lifter height and fill level allowing them to be estimated from measurements of the key charge locations. These could be used as part of a control strategy for the mill and/or to assist with re-line scheduling.