The influence of occupation on lumbar sagittal motion and posture

The aim of this study was to determine whether sheep shearers have clinically hypothesized adaptive postural and sagittal mobility parameters of the lumbar spine and pelvis. Sixty-four shearers and 64 non-shearers, matched by age and anthropometry and surveyed for present and previous low back pain, participated in a study to determine the effects of occupation on sagittal spinal motion and posture. Lumbar and hip mobility measurements were made with a geometric CAD analysis of lateral photographs using surface reflective markers. Sagittal range of motion demonstrated similar ranges of lumbar flexion between the two groups; however, there was a marked gain in hip flexion in the shearers as well as a marked loss of lumbar extension. The shearers also demonstrated a more lordotic lower lumbar curvature compensated by a flatter (less kyphotic) mid to lower thoracic region. Shearers appear to lose lumbar extension, gain hip flexion and develop an adaptive normal stance. This adaptation appears to be independent of previous or current back pain. Conversely, lumbar extension loss in non-shearers correlates with previous back injury. A stepwise linear regression of all participants indicated that the occupation is the predominant influence on motion and posture followed by age. The implications are one of structural adaptation in this occupational group that does not appear to be correlated with back pain.     

The effects of complex wrist and forearm posture on wrist range of motion.

Previous research on wrist functionally has focused almost entirely on range of motion (ROM) in 2 or 3 isolated planes (flexion/extension, radial/ulnar deviation, and forearm pronation/supination), without investigating the potential effects of complex wrist/forearm posture on ROM. A quantitative analysis of these effects on wrist ROM was performed. ROM was measured in one plane using both a manual method and an electrogoniometer while the participant maintained a fixed, secondary wrist and forearm posture. The study revealed that combinations of wrist/forearm postures have significant effects on wrist ROM; the largest effects are those of wrist flexion/extension on radial deviation ROM. The study also found that, consistent with previous research, wrist deviation measurements obtained with an electrogoniometer were significantly different from those obtained manually. Biomechanical theories for the results obtained are discussed. This research could be used to enhance ergonomic evaluation techniques by providing a more accurate risk assessment of certain complex wrist postures, particularly those in which wrist flexion/extension is combined with radial deviation.     

The ratio of thoracic to lumbar compression force is posture dependent

Despite the evidence suggesting that between 8% and 55% of manual labourers experience thoracic pain, research on spinal loading during occupational tasks has been almost invariably limited to the lumbar spine. In this study, we determined the ratio of thoracic to lumbar compression force and the relative risk of injury to each region in various postures. Compressive forces on the spine were calculated based on previously reported thoracic and lumbar intradiscal pressures and disc cross-sectional areas. Flexion postures were associated with an approximate doubling in lumbar compression force but only small increases (or even decreases) in thoracic compression. The ratio of thoracic to lumbar compression was above the tolerance ratio (i.e. the ratio of thoracic to lumbar compressive strength) during upright postures and below the tolerance ratio during flexion postures, indicating that upright postures may pose a greater relative risk of injury to the thoracic spine than to the lumbar spine.

Practitioner summary: Previously reported thoracic and lumbar in vivo disc pressures during various postures were compared. The ratio of thoracic and lumbar compression increased during upright postures and decreased in flexed postures, indicating that upright postures may pose a greater risk of injury to the thoracic spine than to the lumbar spine.     

基于运动姿态识别的行人惯性导航算法

针对室内定位惯性导航算法存在累积误差的问题,提出了一种基于运动姿态识别的行人惯性导航算法.在捷联惯性导航算法的基础上,引入了行人脚部姿态识别方法,将行人的位移以单步长为单位进行惯性导航解算.使用姿态识别与零速修正相结合确定每一步的静止时刻,改进步数检测结果,并对行人静止时刻的速度和位置信息进行校正,以降低累积误差;统计前期误差较小的行人惯性导航数据,并建立步频—步长模型,根据行人实时的步频和方向变化对当前步长进行校准,在行人以惯常运动姿态或运动姿态变化时分别采取对应的步长估计算法,以保证导航算法的准确性.实验结果表明:与传统捷联惯性导航算法相比,提出的算法提高了长距离导航的精度.     

The influence of perceptual grouping on motion detection

In this paper, we present a perceptual organization-based method for detecting moving objects from image sequences. To achieve the characteristics of real-time, efficiency, and robustness, a perceptual computation model of edge partitioning and grouping was proposed for the extraction of edge traces on the fly. Each edge trace is made up of generic edge tokens (GETs) which are perceptual features, and defined qualitatively based on the principles of Gestalt laws. Motion detection uses two basic computations: (1) segment motion GETs (MGETs) by computing the gradient differences between GET streams in consecutive frames; and (2) detect motion objects by perceptually grouping MGETs into object clusters. The MGETs in each cluster are constrained by the proximity of the features, and the motion continuation of the cluster measured by motion persistence, etc. Experimental results are provided.     

波动系数对网络结构的影响

根据五类非屏蔽双绞线和网络拓扑结构的特点,结合图论与关系矩阵的相关知识,提出了链路上界和波动系数的概念,并对其进行了详细的分析.通过对波动系数的讨论,给出了网络性能优劣判定的建议方法.     

The influence of virtual human model appearance on visual ergonomics posture evaluation

The objective of this study was to investigate whether the appearance of virtual human models influences observers when judging a working posture. A task in which a manikin is manually assembling a car battery was used in the experiment. In total, 16 different pictures were presented to the subjects. All pictures had the same background, but included a unique posture and manikin appearance combination. 24 subjects consisting of manufacturing managers, simulation engineers and ergonomists were asked to rate and rank the pictures. The results showed that the virtual human model appearance influenced subjects when they rated pictures one by one: a more realistic manikin was rated higher than the identical posture visualized with a less natural appearance. This appearance effect was not seen when subjects ranked the pictures while looking at all of them at the same time. The study demonstrates that the human modelling tool used when showing and visually evaluating results makes a difference. To minimize subjective effects, a combination of visualizations and objective ergonomic assessment methods is recommended.     

The influence of posture on power output generated in single pulling movements

The power generated in single pulling movements in seated and standing postures was measured by means of novel dynamometers. The power available is strongly dependent upon the resistance to movement, as well as the posture. Some of the results have been applied to an assessment of the matching of outboard motors to their users, illustrating an ergonomic value of the methodology.     

Estimation of compressive forces on lumbar spine from categorical posture data

To combine estimates of trunk posture and force into an integrated measure of load on the low back, continuous variables for body angles were estimated by assuming specified distributions within corresponding posture categories with Monte-Carlo (MC) simulation. The estimated posture angles were compared with reference measurements from the Lumbar Motion Monitor and inclinometers. The lumbar compression estimates, generated from simulated posture angles and from direct measurement, were compared. Trunk flexion showed high correlation between direct measurements and simulated angles, as did L5/S1 compression. The MC approach to extracting continuous posture angles from categorized observations did not appear to introduce large error in the variables used to estimate spinal compressive forces. When instrumentation methods of postural assessment are not feasible, a simulation approach combined with biomechanical modelling could be used to integrate multiple external exposure variables into estimates of compressive forces acting on the low back.     

Estimation of compressive forces on lumbar spine from categorical posture data

To combine estimates of trunk posture and force into an integrated measure of load on the low back, continuous variables for body angles were estimated by assuming specified distributions within corresponding posture categories with Monte-Carlo (MC) simulation. The estimated posture angles were compared with reference measurements from the Lumbar Motion Monitor and inclinometers. The lumbar compression estimates, generated from simulated posture angles and from direct measurement, were compared. Trunk flexion showed high correlation between direct measurements and simulated angles, as did L5/S1 compression. The MC approach to extracting continuous posture angles from categorized observations did not appear to introduce large error in the variables used to estimate spinal compressive forces. When instrumentation methods of postural assessment are not feasible, a simulation approach combined with biomechanical modelling could be used to integrate multiple external exposure variables into estimates of compressive forces acting on the low back.     

The influence of ship motion on manual control skills

The effects of ship motion on a range of typical manual control skills were examined on the Warren Spring ship motion simulator driven in heave, pitch and roll by signals taken from the frigate H MS Avenger at 13m/s(25 knots) into a force 4 wind. The motion produced a vertical r.m.s. acceleration of 0024g, mostly between 01 and 0-3 Hz, with comparatively little pitch or roll. A task involving unsupported arm movements was seriously affected by the motion; a pursuit tracking task showed a reliable decrement although it was still performed reasonably well (pressure and free-moving tracking controls were affected equally by the motion); a digit keying task requiring ballistic hand movements was unaffected. There was no evidence that these effects were caused by sea-sickness.

The differing response to motion of the different tasks, from virtual destruction to no effect, suggests that a major benefit could come from an attempt to design the man/control interface on board ship around motion resistant tasks.     

The between-day and inter-rater reliability of a novel wireless system to analyse lumbar spine posture

Lumbar posture is commonly assessed in non-specific chronic low back pain (NSCLBP), although quantitative measures have mostly been limited to laboratory environments. The BodyGuard? is a spinal position monitoring device that can monitor posture in real time, both inside and outside the laboratory. The reliability of this wireless device was examined in 18 healthy participants during usual sitting and forward bending, two tasks that are commonly provocative in NSCLBP. Reliability was determined using intraclass correlation coefficients (ICC), the standard error of measurement (SEM), the mean difference and the minimal detectable change (MDC90). Between-day ICC values ranged from 0.84 to 0.87, with small SEM (5%), mean difference (<9%) and MDC90 (<14%) values. Inter-rater ICC values ranged from 0.91 to 0.94, with small SEM (4%), mean difference (6%) and MDC90 (9%) values. Between-day and inter-rater reliability are essential requirements for clinical utility and were excellent in this study. Further studies into the validity of this device and its application in clinical trials in occupational settings are required. STATEMENT OF RELEVANCE: A novel device that can analyse spinal posture exposure in occupational settings in a minimally invasive manner has been developed. This study established that the device has excellent between-day and inter-rater reliability in healthy pain-free subjects. Further studies in people with low back pain are planned.     

The influence of rice plow handle design and whole-body posture on grip force and upper-extremity muscle activation

A previous job screening study revealed ergonomics risk factors in rice field plowing. This work motivated the present experimental investigation of the influence of plow handle design and farmer whole-body posture on grip force and arm muscle activity. A total of 24 experienced farmers performed a simulated plowing task, including walking on even and uneven ground while rolling a tiller equipped with conventional horizontal and proposed vertical handles. Results revealed the proposed handles, designed to promote neutral wrist posture, to increase upper-arm muscle use between 47% and 70% across ground types, as compared with conventional handles. The ratio of grip force to forearm muscle activity (or efficiency in muscle use) increased from 1.85 when using conventional handles on uneven ground to 2.16 when using the proposed handles with symmetrical body posture on even ground. However, participants perceived higher discomfort when using the proposed handles, as they were accustomed to the conventional design.     

Effects of seated lumbar extension postures on spinal height and lumbar range of motion during prolonged sitting

Prolonged sitting during sedentary work has been reported as a potential risk factor for low back pain. Furthermore, prolonged sitting can result in both reduced spinal height (SH) and lumbar range of motion (LROM). This study compared the effects of no intervention (control) with two recovery postures on SH and LROM (flexion and extension) during prolonged sitting. Twenty-four participants were randomly assigned to three interventions for three consecutive days. The interventions comprised two seated lumbar extension recovery postures (unsupported sustained and supported dynamic lumbar extension postures) and a control. Both interventions facilitated a relatively short recovery period for both SH and LROM. Supported dynamic lumbar extension conditions significantly helped SH recovery, as compared with control condition, after the first recovery posture intervention, and both postures have potential to maintain LROM. However, both postures failed to induce SH recovery over an extended time.     

Sitting posture: analysis of lumbar stresses with upper limbs supported

The analysis of lumbar stresses in the sitting posture is performed for situations in which upper limbs are fully or partially supported by a worktable. A method is presented for biomechanical evaluation of moments and compressive forces acting on the lumbar intervertebral disk, based on the use of a force platform, a TV camera and a integrated system for the elaboration of signals. The on-line pictures given by this equipment show the ground reaction vector superimposed on the subject's image and allows a detailed analysis of the intervertebral loads. The results obtained in the subjects under study (six males and five females) are analysed statistically and extrapolation on the basis of body weight is demonstrated to be possible in situations where the arm support forces are not known. The myoelectric activity of the erector spinae muscles was also assessed.

The aim of the study was to furnish a tool that can be used in all occupational environments and that will allow evaluation of the lumbar stresses in the sitting posture to be made with a minimum use of complex equipment. An example of the practical application of this concept is presented.     

The influence of desk and display design on posture and muscle activity variability whilst performing information technology tasks

Desk design and computer display height can affect posture and muscle activation during computer use. Amplitudes of postural variables and muscle activity during computer use do not explain the results from epidemiological studies of musculoskeletal discomfort and disorders related to computer use. The purpose of this study was to assess variability of posture and muscle activity during work with two computer display heights and book/paper, in conjunction with a curved desk designed to provide forearm support and a traditional, straight desk.18 male and 18 female participants performed 10-min tasks involving keying, mousing, reading and writing in six desk/display conditions. 3D posture and surface emg were assessed for the final 2 min of each task.The curved desk resulted in greater postural and muscle activity variation, suggesting an advantage of this supportive surface over the straight desk. There was little difference in variability associated with the two display heights. However, greater variability of posture and muscle activity was evident with the book/paper condition. Non-touch typists had greater neck flexion variation.The design of information technology tasks and workstations can influence the short term variation in posture and muscle activity. Variation is influenced independently of mean postures and muscle amplitudes and therefore needs to be considered to adequately assess the risk of musculoskeletal disorders.     

Muscle activity and range of motion during active trunk rotation in a sitting posture

Twisted trunk postures during tractor driving are associated with low-back pain. The purposes of this study were to quantify the muscle activity as a function of twisting angle, to quantify the range of motion (ROM) during active trunk rotation and to determine whether there were any differences between tractor drivers and office workers and between twisting direction for these variables. The subjects performed exertions in a seated position, twisting from the neutral position to the end of the ROM. The results showed that external oblique and erector spinae had significantly different activation patterns depending on twisting direction. For the contralateral external oblique and the ipsilateral erector spinae, the muscle effort required to twist the trunk was low up to about 20° twisting angle, then the muscle effort needed to twist the trunk increased progressively. No significant differences due to occupation or twisting direction were found. The result implies that work in twisted trunk postures might be a risk factor for low-back pain.