Relation between spinal load factors and the high-risk probability of occupational low-back disorder

Spinal compression is traditionally assumed the principal biomechanical mechanism associated with occupationally related low-back disorders (LBD). However, there is little conclusive evidence demonstrating that compression is related to occupational LBD. The objective of this research was to examine whether axial compression in the lumbar spine can predict the probability that a lifting task should be classified as high risk for LBD. Furthermore, the improvement in predictive ability was examined when analyses include 3-D, dynamic biomechanical factors. Ten experienced warehouse workers transferred 12 pallet loads of boxes in a simulation of warehouse working conditions. Biomechanical estimates of 2-D static and 3-D dynamic spinal compression, shear loads and tissue strains were achieved from the subjects during each lifting exertion. Each lift was also assessed for probability of high LBD risk classification. Regression analyses were performed to examine the relationship between biomechanical and epidemiological factors. Results indicate 2-D static estimates of spinal compression describe ? 13% of the probability of high LBD risk variability. Dynamic estimates of spinal compression describe >44% of the variability. A multifactor regression model including 3-D spinal loads and tissue strains further improved the predictive ability, but the improvement was not statistically significant. This research demonstrates the biomechanical source of low-back pain is dynamic, multifaceted and multidimensional. Significant improvements in ergonomics assessments can be achieved by examining interactions of dynamic biomechanical factors. Unfortunately, this improved predictive ability is generated at the high cost of computational complexity. However, less realistic biomechanical representations may ignore the injury mechanisms associated with the greater number of workplace injuries. Thus, improved understanding of the dynamic biomechanical interactions influencing the tolerance and injury mechanisms of the spine may permit more accurate assessments of workplace injury factors associated with LBD and reduced incidence of occupationally related low-back pain.     

Review of: “ Systems Documentation: Techniques of persuasion in large organizations”. By FRANK WHITEHOHSE, ( London: Business Books, 1973.) [Pp. viii + 191.] £450.

The use of back belts in industry has increased despite the lack of scientific evidence supporting their efficacy. The purpose of this study was to investigate the effect of a semi-rigid lumbosacral orthosis (SRLSO) on oxygen consumption during 6-min submaximal repetitive lifting bouts of 10 kg at a lifting frequency of 20 repetitions min^-1. Fifteen healthy subjects (13 men, two women) participated in this study. Each subject performed squat and stoop lifting with and without an SRLSO for a total of four lifting bouts. Lifting bouts were performed in random order. Oxygen consumption during the final minute of each lifting bout was used for analysis. A two-way analysis of variance with repeated measures was used to analyse the effects of lift and belt conditions. The stoop and squat methods were significantly different, with the squat lift requiring 23% more oxygen on average than the stoop lift for equal bouts of work. No significant difference was found between the belt and no belt condition within the same lifting technique and no interaction was present. These data suggest that an SRLSO does not passively assist the paravertebral muscles (PVM) in stabilizing the spine during submaximal lifting bouts.     

Inter-rater reliability of a video-analysis method measuring low-back load in a field situation

Valid and reliable low-back load assessment tools that can be used in field situations are needed for epidemiologic studies and for ergonomic practice. The aim of this study was to assess the inter-rater reliability of a low-back load video-analysis method in a field setting.     

An investigation of perceived exertion via whole body exertion and direct muscle force indicators during the determination of the maximum acceptable weight of lift

The objective of this study was to identify the perceived exertion mechanisms (direct muscle force and whole body exertion) associated with the decision to change the weight of lift during the determination of the maximum acceptable weight of lift (MAWL). Fifteen males lifted a box of unknown weight at a rate of 4.3 lifts/min, and adjusted the weight until their MAWL was reached. Variables such as the predicted muscle forces and heart rate were measured during the lifting exertion, as well as the predicted spinal loading in three dimensions using an EMG-assisted biomechanical model. Multiple logistic regression techniques were used to identify variables that were associated with the decision to change the weights up and down prior to a subsequent lift. Results indicated that the force in the left erector spinae, right internal oblique, and left latissimus dorsi muscles as well as heart rate were associated with decreases in the weight prior to the next lift. It appears that a combination of local factors (muscle force) and whole body exertion factors (heart rate) provide the feedback for the perceived exertion when decreasing the weight. The up-change model indicated that the forces of the right erector spinae, left internal oblique, and the right latissimus dorsi muscles were associated with the decision to increase the weight prior to the next lift. Thus, local factors provide feedback during the decision to increase the weight when starting from light weights. Collectively, these findings indicate that psychophysically determined weight limits may be more sensitive to muscular strain rather than spinal loading.     

Do workplace interventions prevent low-back disorders? If so,why?: a methodologic commentary

The demand for workplace interventions to prevent low-back disorders has increased in recent years. At the same time, a crisis in the literature has become apparent: there are conflicting reports on whether or not these interventions work. With the aim of understanding the reason for the dissension in the literature, six studies were selected for close examination. These were studies of interventions based on differing principles, i.e. a change in organizational ethos to promote back safety, back belt use, the introduction of ergonomic devices, and back-strengthening exercises. If the studies are taken at face value, any of the interventions, regardless of type, has a tremendous effect. Methodological problems inherent in these studies may provide a clue to why essentially different interventions were found to be consistently successful. Study design quality has long been noted to exert a particular influence on the evaluation of outcomes: the quality of the study design is often inversely related to reported outcomes. Of the six studies selected for examination, four did not include a contemporaneous control group, five did not randomly assign subjects to test and control groups, and none included a placebo group. Given these research designs, variables other than those tested by the studies may have produced the reported results. These variables include ‘beliefs of the intervention providers’ and ‘coalescence of the work group ’, both of which are discussed. Two approaches, the pragmatic and the explanatory, may be used to study workplace interventions to prevent low-back disorders. Most of the examined studies are pragmatically oriented. Having dealt with study design problems expeditiously, these studies may be characterized as more immediately responsive to the demand to evaluate workplace interventions than explanatory studies. On the other hand, explantory studies, most notably associated with randomized clinical trials in medicine, are more rigorous. Enough pragmatically oriented studies have been conducted to suggest that workplace interventions may have an effect on low-back disorders. More conclusive explanatory studies may now be conducted.     

Lifting belts: a psychophysical analysis

The literature supporting the use of lifting belts has not demonstrated consistent trends. It was hypothesized that if lifting belts provide a biomechanical or motivational advantage then the participants in a psychophysical lift test should select a higher maximum acceptable weight of lift (MAWL). Eleven male and five female subjects participated in one session with a lifting belt and one session without a belt. The order of the belt sessions was counterbalanced. Each session was comprised of two psychophysical lifting tests varying only in the initial weight of the box. Repeated measures ANOVA showed no difference between the MAWL between belt sessions or between the two tests within a given session. Following the test, subjective evaluations of the belt were measured via a questionnaire. The psychophysical test results showed no change as a function of the belt condition. Thus, these results do not support the hypothesis that lifting belts increase trunk strength or motivate individuals to select a greater MAWL. Therefore, it must be concluded that belts do not offer a biomechanical or motivational advantage to the user.     

Lumbosacral compression in maximal lifting efforts in sagittal plane with varying mechanical disadvantage in isometric and isokinetic modes

Nine normal male subjects (mean age 28·2 years and mean weight 72·6 kg) performed 20 standardized maximal effort lifting tasks. They were asked to perform stoop and squat lifts at half, three-quarters and full individual horizontal reach distances in mid-sagittal plane in isometric and isokinetic modes (fixed velocity 60 cm/s). Both stoop and squat lifts were initiated at the floor level and terminated at the individual's knuckle height keeping the horizontal distance constant throughout the lift. The isometric stoop lifts were performed with hip at 60° and 90° of flexion with hands at preselected reach distances. The isometric squat lifts were performed with knees at 90° and 135° of flexion with hands at similarly preselected reach distances. The force was measured using a Static Dynamic Strength Tester with load cell (SM1000). The postures were recorded using a two-dimensional Peak Performance System with an event synchronizing unit. The load cell was sampled at 60 Hz and the video filming was done at 60 frames per second. The force and postural data were fed to a biomechanical model (Cheng and Kumar 1991) to extract external moment and lumbosacral compression. The strengths generated in different conditions were significantly different (p < 0·01). The strength variation ranged by up to 73% whereas the lumbosacral compression varied by only up to 15%. A high level of lumbosacral compression was maintained in all conditions.     

Occupational low back disorder causation and control

Low back disorders (LBDs) continue to be the most common musculoskeletal problem in the workplace. It affects many workers, is associated with high costs to industry and the individual, and can negatively influence the quality of life for the workers. Currently there is significant controversy about the work-relatedness of LBD and the ability of ergonomics interventions to control the problem. This paper systematically examines the body of knowledge associated with LBDs and considers how information from different disciplines of study collectively might be used to assess the causality and control of LBD due to physical factors associated with work.     

The use of turnover rate as a passive surveillance indicator for potential low back disorders

Passive surveillance techniques which rely only on injury reporting to locate ergonomic problems within a facility may not be sensitive enough to identify all jobs that place a worker at risk of low back disorder. The current study examines whether turnover rate data provide useful input to a passive surveillance approach. It is hypothesized that the turnover of employees through individual jobs, when not attributable to differential pay scales within a facility, is likely to indicate the presence of ergonomic hazards associated with low back cumulative trauma disorders. This study used the database and multiple logistic regression model developed by Marras et al. (1993) to evaluate this hypothesis. Two data sets were evaluated with the model to determine whether jobs with turnover resemble those with a high historical risk of LB-CTD. The first data set contained trunk motion and workplace data from jobs in which there had been turnover but there were no incidents of LB-CTD. When comparing these data to truly low risk jobs (no LB-CTD incidents or turnover), the model yielded an odds ratio of 5·2. This moderate odds ratio indicates that many of the jobs with turnover have characteristics similar to those found in high LB-CTD risk jobs. The second data set included jobs with turnover and moderate LB-CTD incident rates. The model's resulting odds ratio of 11·0 indicates that jobs with moderate incident rates and turnover are very similar to jobs with a high LB-CTD risk. These results suggest that passive surveillance programs would be more sensitive if turnover rates were determined for each job within a facility and were used to supplement incident rate data.     

Biomechanical evaluation of heavy tool-handling in two age groups of firemen

The biomechanical load of a rescue-clearing task (lifting a power saw from the floor up to the ceiling level) was evaluated with six older (47 ± 5 years) and seven younger firemen (32 ± 2 years). The mean dynamic compressive force at the L5/SI disc was 5998?N for the older subjects and 6392?N for the younger subjects. The peak torques for the back and knee extensions were about equal for the two groups of the subjects. The younger subjects had a significantly higher movement speed in the knee extension than the older subjects (89.1 ± 25.7 vs. 35.3±11.5°/, p<0.001). The results showed that lifting a power saw produced a high load on the musculoskeletal system, and that the load was not influenced by age.     

基于自适应提升方案的嵌入式系统信息压缩编码

嵌入式系统中信息受存储空间的限制,因而有必要对系统中存储和传输的信息进行压缩;本文通过采用自适应提升小波分析,根据嵌入式系统中存储和传输的信息局部特征调整预测和更新算子,实现与处理信息自适应的匹配,有效地降低信息小波分析的运算量和计算的复杂性,并且能较好地在系统中实现同址运算,降低了系统设计的复杂性和设计成本。同时,通过定义浮动阈值,提高了信息渐进式编码的搜索效率。仿真结果表明,本文算法在一定程度上提高了信息压缩的效果。     

基于自适应提升方案的嵌入式系统信息压缩编码

嵌入式系统中信息受存储空间的限制，因而有必要对系统中存储和传输的信息进行压缩：本文通过采用自适应提升小波分析，根据嵌入式系统中存储和传输的信息局部特征调整预测和更新算子，实现与处理信息自适应的匹配,有效地降低信息小波分析的运算量和计算的复杂性，并且能较好地在系统中实现同址运算，降低了系统设计的复杂性和设计成本。同时，通过定义浮动阈值，提高了信息渐进式编码的搜索效率。仿真结果表明，本文算法在一定程度上提高了信息压缩的效果。     

ERGONOMICS IN THE DESIGN OF A LARGE DIGITAL COMPUTER CONSOLE

Posture plays a fundamental role in the knowledge which the operator has of his work space and in the gauging of the actions he performs there. Seen in this light, posture is a means of constructing a spatial reference and a spatial reference in itself. Some results of experiments and others obtained at the workplaces show a relation between speed and precision required for the task and postural immobility. Postural immobilization for a period of several hours is poorly tolerated and has serious consequences: it explains the neck, shoulder and back pains frequently experienced in these situations. These consequences, combined with the constraints of speed and precision, make such jobs unsuitable for persons above a certain age.     

Spine loading and trunk kinematics during team lifting

Two-person or team lifting is a popular method for handling materials under awkward or heavy lifting conditions. While many guidelines and standards address safe lifting limits for individual lifting, there are no such limits for team lifting, and these lifts are poorly understood. The literature associated with team lifting offers some interesting paradoxes. Many studies have indicated that people lift less per individual under team conditions compared with one-person lifting. Yet, at least one study has reported an increase in team-lifting capacity when subjects were height-matched. The current study explored the spine loading characteristics of one- and two-person lifting teams when subjects lifted under several sagittally symmetric and asymmetric conditions. Spine compression was lower for two person lifts for a given weight, while lifting in sagittally symmetric conditions whereas lateral shear became much greater for two-person lifts under asymmetric lifting conditions. This study has linked these changes to differences in trunk kinematic patterns adopted during one- versus two-person lifting.     

H.264/AVC编码模式选择

H．264／AVC是最新的视频编码标准。与以前的视频标准相比编码模式更多,压缩效率更高,同时在编码模式的选择上也更复杂,计算量更大。编码时如何选择合适的编码模式对H.264／AVC的压缩性能和计算复杂度是非常关键的。本文讲述了JVT的参考软件是如何实现H．264／AVC编码模式选择。     

A COMPARISON OF TWO SUBSIDIARY TASKS USED TO MEASURE FATIGUE IN CAR DRIVERS

Abstract

Car driving has been studied by combining it with a subsidiary task, performance on which is negatively correlated with the perceptual load imposed by changing conditions of traffic. The present experiment compares a subsidiary task which required almost continuous attention to an auditory display, and which involved memory spans of only 3 sec, with an alternative task which did not require continuous attention, but which involved memory spans of up to 55 sec. The former was found to have some advantages. This comparison was combined with a study of men engaged in 8-hour spells of car driving. Some explanations are offered for the finding that performance on the subsidiary tasks was better at the end of the work-spell than at the beginning.     

可扩展视频编码中运动补偿时域滤波的改进

在基于小波变换的可扩展视频编码方案中,研究运动补偿时域滤波的优化方法.将有效的多相位子带内运动估计纳入分层运动估计策略中,用提升算法实现子带内运动补偿时域滤波,融入多假设预测以优化运动补偿技术;为了提高低码率下视频编码的可扩展性,提出更新算子的优化设计.实验结果显示,在保证运动估计精度下,合理选择时间滤波器,结合改善的提升实现中的更新操作,提高了编码系统的编码效率和可扩展性能.     

力控方案中抑制机械手冲击的策略

本文讨论了机器人力控方案中，抑制碰撞时冲击力的控制策略，文中提出了发生碰撞时的模型，在此基础上分析了两种策略得到的结论，实验结果与理论分析相一致，都指出积分算法能得到满意的抑制冲击的效果。     

THE USE OF DECRYPTED GERMAN WEATHER REPORTS IN THE OPERATIONS OF THE FIFTEENTH AIR FORCE OVER EUROPE

German weather reports were decrypted swiftly enough to enable 15th Air Force meteorologists to use them, together with reports from Allied and neutral sources, to predict the rare times of the perfectly clear weather required to bomb targets visually in Central Europe. There was an average of only two suitable days per month and these were barely enough to complete the attacks that neutralized the Luftwaffe in time for D-Day. Without these reports there would have been many futile missions to cloud-covered targets with much loss of lives and planes.