Vibrations transmitted from human hands to upper arm,shoulder, back,neck, and head

Some powered hand tools can generate significant vibration at frequencies below 25 Hz. It is not clear whether such vibration can be effectively transmitted to the upper arm, shoulder, neck, and head and cause adverse effects in these substructures. The objective of this study is to investigate the vibration transmission from the human hands to these substructures. Eight human subjects participated in the experiment, which was conducted on a 1-D vibration test system. Unlike many vibration transmission studies, both the right and left hand-arm systems were simultaneously exposed to the vibration to simulate a working posture in the experiment. A laser vibrometer and three accelerometers were used to measure the vibration transmitted to the substructures. The apparent mass at the palm of each hand was also measured to help in understanding the transmitted vibration and biodynamic response. This study found that the upper arm resonance frequency was 7–12 Hz, the shoulder resonance was 7–9 Hz, and the back and neck resonances were 6–7 Hz. The responses were affected by the hand-arm posture, applied hand force, and vibration magnitude. The transmissibility measured on the upper arm had a trend similar to that of the apparent mass measured at the palm in their major resonant frequency ranges. The implications of the results are discussed.Relevance to industryMusculoskeletal disorders (MSDs) of the shoulder and neck are important issues among many workers. Many of these workers use heavy-duty powered hand tools. The combined mechanical loads and vibration exposures are among the major factors contributing to the development of MSDs. The vibration characteristics of the body segments examined in this study can be used to help understand MSDs and to help develop more effective intervention methods.     

Concurrent validation of magnetic and inertial measurement units in estimating upper body posture during gait

We assessed the concurrent validity of commercially available magnetic and inertial measurement units (MIMUs) for estimating mean postural angles for head flexion, thorax flexion and shoulder girdle elevation during gait in seven healthy individuals. Postural angles estimated with the MIMUs were compared with angles calculated using marker data from a gold standard motion capture system. Coefficients of determination of mean postural angles between measurement systems were 0.82 for head flexion, 0.58 for thorax flexion, and 0.77 for shoulder girdle elevation. Bland–Altman analysis showed good agreement between measurement systems. Intraclass correlation coefficients were 0.9 for head flexion, 0.73 for thorax flexion, and 0.87 for shoulder girdle elevation. Root mean square errors were less than 3° between measurement systems for all body segments. The present findings suggest that the MIMUs tested in this study are valid for estimating head flexion, thorax flexion and shoulder girdle elevation during gait.     

Significance of house painters' work techniques on shoulder muscle strain during overhead work

House painters represent a group of construction workers with a high frequency of neck and shoulder complaints and concomitant high risks for early retirements. Shoulder tendinitis, especially supraspinatus tendinitis, occurs frequently among house painters. The tasks of sanding and painting of ceilings with extension handles are particularly strenuous for these body regions. The purpose of this study was to identify work techniques that would be less strenuous to the arms and shoulders during sanding work. A biomechanical model was applied to quantify the shoulder loads during sanding and to determine the likely muscle force distribution. The necessary input data were measured experimentally for the model by means of a load cell and strain gauges on an extension handle, a Kistler force plate, and a MacReflex motion analysis system. Forty experienced male painters participated in the study. Three different work techniques were identified: the normal technique, the reversed grip and the pushing technique. The pushing technique was characterized by shorter stroke length and lower speed of the grinding block than the other techniques. The painters among the group of subjects who used the pushing technique were found to report fewer shoulder disorders during sanding than the others. The most common shoulder tendinitis is the supraspinatus tendinitis, also among house painters, and using the Pushing technique could possibly prevent from this disorder. However, further research in larger groups of house painters is needed to be able to recommend this technique for a wider use.     

Muscle fatigue during intermittent isokinetic shoulder abduction: Age effects and utility of electromyographic measures

Most existing evidence regarding the effects of age on muscular fatigue has focused on prolonged isometric contractions, repeated maximum dynamic contractions and individuals beyond traditional retirement age (>65 years). In the present study, age-related differences in muscle fatigue during submaximal dynamic efforts were examined. There were 24 younger (18–25 years) and 24 older (55–65 years) participants, all of whom were healthy and active, with equal numbers of each gender within each age group. Participants performed repetitive, intermittent shoulder abductions until exhaustion, at peak moments of 30% and 40% of individual maximum voluntary isokinetic contraction (MVIC) and with cycle durations of 20 and 40 s. Fatigue development was determined based on changes in MVIC, electromyographic (EMG) signals and ratings of perceived discomfort (RPD). Following the exhaustive exercises, strength recovery was monitored using a series of MVICs over a 15-min period. Results indicated the existence of an age-related fatigue resistance, with the older group demonstrating significantly slower rates of MVIC decline and RPD increase and smaller modifications in EMG-based fatigue measures. These age effects were generally more pronounced at the higher effort level. Main effects of effort level and cycle duration were also significant, while gender effects appeared to be marginal. Rates of strength recovery were not significantly influenced by age. In addition, the utility of standard EMG-based fatigue measures was assessed. Findings indicated that time-dependent changes in static and dynamic EMG-based measures were roughly comparable in terms of sensitivity and variability, supporting the use of standard EMG analyses for fatigue monitoring during intermittent dynamic contractions.     

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.     

基层民众与私盐——清中叶两淮盐区流通领域的私盐问题研究

清中叶,两淮盐区流通领域的私盐异常活跃,这些私盐的贩卖主体主要为肩挑背负之民、船户水手和流民等基层民众。本文通过大量的个案,分析了上述基层民众贩卖私盐的原因、表现形式及其影响与危害性等。     

Relating crash frequency and severity: Evaluating the effectiveness of shoulder rumble strips on reducing fatal and major injury crashes

To approach the goal of “Toward Zero Deaths,” there is a need to develop an analysis paradigm to better understand the effects of a countermeasure on reducing the number of severe crashes. One of the goals in traffic safety research is to search for an effective treatment to reduce fatal and major injury crashes, referred to as severe crashes. To achieve this goal, the selection of promising countermeasures is of utmost importance, and relies on the effectiveness of candidate countermeasures in reducing severe crashes. Although it is important to precisely evaluate the effectiveness of candidate countermeasures in reducing the number of severe crashes at a site, the current state-of-the-practice often leads to biased estimates. While there have been a few advanced statistical models developed to mitigate the problem in practice, these models are computationally difficult to estimate because severe crashes are dispersed spatially and temporally, and cannot be integrated into the Highway Safety Manual framework, which develops a series of safety performance functions and crash modification factors to predict the number of crashes. Crash severity outcomes are generally integrated into the Highway Safety Manual using deterministic distributions rather than statistical models. Accounting for the variability in crash severity as a function geometric design, traffic flow, and other roadway and roadside features is afforded by estimating statistical models. Therefore, there is a need to develop a new analysis paradigm to resolve the limitations in the current Highway Safety Manual methods. We propose an approach which decomposes the severe crash frequency into a function of the change in the total number of crashes and the probability of a crash becoming a severe crash before and after a countermeasure is implemented. We tested this approach by evaluating the effectiveness of shoulder rumble strips on reducing the number of severe crashes. A total of 310 segments that have had shoulder rumble strips installed during 2002–2009 are included in the analysis. It was found that shoulder rumble strips reduce the total number of crashes, but have no statistically significant effect on reducing the probability of a severe crash outcome.     

Subjective and objective evaluation of shoulder muscle fatigue

In order to relate EMG signs of localized muscle fatigue to subjectively perceived muscle fatigue, a study was undertaken on 20 healthy volunteers exposing their right trapezius muscle by raising the arm to 90° of abduction. Every person performed two contractions: 0 kg hand load during 5 min and 2 kg hand load during 2.5 min. Surface EMG was recorded and analysed with respect to RMS amplitude and mean power frequency (MPF). Subjective muscle fatigue was estimated with a psychophysical rating scale (Borg's CR-10 Scale). At high load level we found a significant correlation between MPF and the CR-scores (r = ? 0.46), but at low load level there was no correlation. At high load level there was a linear decrease of MPF with increasing load dose, but at low load level the MPF did not change, despite significant subjective fatigue. There was a linear rise of the CR-score with increasing load dose, more pronounced at high load level. It was concluded, that at low load levels common in working life, MPF and subjective scores seem to provide different fatigue information. Moreover, the MPF did not seem to work as a valid estimator of muscle fatigue at this low load level. Caution is recommended if it is to be used in static low-load situations.     

Ergonomic evaluation of masons laying concrete masonry units and autoclaved aerated concrete

Masons working with concrete masonry unit block have high rates of work-related musculoskeletal disorders to the low back and shoulders associated with repetitively lifting and buttering heavy block. A new material, autoclaved aerated concrete, may reduce the risk of shoulder and back injury but, ergonomic evaluation is needed. This study evaluated shoulder exposure parameters, low back stress, and worker perceptions in two groups of journey level masons, one using CMU and the other using AAC block. Results indicate that for the left arm AAC masons spent significantly more time than CMU masons in static (38.2% versus 31.1%, respectively), and less time in slow motions (48.2% versus 52.2%, respectively) and faster motions (13.6% versus 16.7%, respectively) (p < 0.05). CMU masons had significantly greater shoulder and low back pain (p = 0.009) and they held block significantly longer than AAC masons (p < 0.001). Low back compressive forces were high for both materials. Masons handling AAC demonstrated less left upper extremity stress but both materials were estimated to be hazardous to the low back.     

小湾坝肩槽开挖边坡的三维刚体弹簧元分析

采用三维非线形刚体弹簧元法，对小湾坝肩槽开挖边坡进行应力应变及稳定分析，对计算成果进行评价分析，进而评价了工程加固措施。计算出各工况下滑面、滑块的安全系数，对计算成果进行了评价分析，并进行破坏模式的研究，提出了工程加固措施，从而为提高边坡开挖加固措施提供了依据。