Trunk kinematics of one-handed lifting,and the effects of asymmetry and load weight

Abstract

This study investigated trunk kinematic differences between lifts performed using either one hand (unsupported) or two hands. These effects were studied while beginning the lifts from different asymmetric starting positions and while lifting different load weights. Each subject lifted a box from a lower to an upper platform under one- and two-handed lifting conditions. Subjects wore a lumbar spine electrogoniometer, from which relative motion components were calculated in the trunk's three cardinal planes. Results of this study showed that one-handed lifting resulted in significantly higher ranges of motion in the lateral and transverse planes and greater flexion in the sagittal plane. Back motion characteristics previously found to be associated with low back disorders were all significantly higher for one-handed lifts. The two-handed lift technique, on the other hand, produced overall faster trunk motions in the sagittal plane and equal or larger acceleration and deceleration magnitudes in all planes of motion. Increases in load asymmetry affected trunk kinematics, in that magnitude values for range of motion, velocity and acceleration became much greater with increasingly asymmetric load positions. Increasing the load weight appeared to have less of an effect on trunk kinematics, with increases in position mostly occurring during sagittal and lateral bending. These results suggest that unsupported one-handed lifting loads the spine more than two-handed lifts, due to the added coupling. Applying these results to a previously developed model, one-handed lifting was also found to increase one's risk of suffering a low back disorder.     

The measurement and prediction of isometric lifting strength in symmetrical and asymmetrical postures.

Static lifting strengths of nine men and nine women were measured at six heights from just above the floor to just above the head, at two horizontal reaches from the mid-ankles (equal to the elbow to grip and acromium to grip distances), in the sagittal plane and also at 45 degrees and 90 degrees to the right for two-handed exertions and at 45 degrees and 90 degrees to each side for one-handed exertions, making a total of 96 postures. A second and different group of 18 subjects (nine men and nine women) were studied in 20 two-handed and 40 one-handed postures intermediate to those of the first group. A third group of 16 subjects (eight men and eight women), with six drawn from the other groups, were used to determine maximum possible reach (at which lifting strength is zero) at the same heights and planes as those for the first group. When strength was expressed as a fraction of body weight and height and reach were expressed as fractions of stature, predictive equations of static lifting strength were obtained which were gender free. The predictive equations may be used to generate isodyne contours for an individual in any chosen planes. Individuals exist whose strengths are consistently greater or less than the prediction. The possibility of identifying such persons in a process of worker selection is discussed.     

Use of the analytic hierarchy process in ergonomic analysis

The paper deals with the application of the Analytic Hierarchy Process (AHP) in decision making and conflict resolution for ergonomic evaluation. The procedure is illustrated through the selection of Manual Materials Handling Guidelines by comparing NIOSH standards with European Coal and Steel Community (ECSC) lifting guidelines. Based on 11 criteria proposed by Frievalds (1987), the NIOSH Lifting Guidelines have been found to better represent sagittal two-handed lifting than the ECSC guidelines. The implications of the adaptation of the procedure are briefly discussed.     

The effect of a lower extremity kinematic constraint on lifting biomechanics

Leaning against a stationary barrier during manual materials handling tasks is observed in many industrial environments, but the effects of this kinematic constraint on low back mechanics are unknown. Thirteen participants performed two-handed lifting tasks using both a leaning posture and no leaning posture while trunk kinematics, muscle activity and ground reaction force were monitored. Results revealed that lifting with the leaning posture required significantly less activity in erector spinae (26% vs. 36% MVC) and latissimus dorsi (8% vs. 14% MVC), and less passive tissue moment compared with the no leaning posture. Peak sagittal accelerations were lower when leaning, but the leaning posture also had significantly higher slip potential as measured by required coefficient of friction (0.05 vs. 0.36). The results suggested that the leaning lifting strategy provides reduced low back stress, but does so at the cost of increased slip potential.     

Spinal loading when lifting from industrial storage bins

The study documented three-dimensional spinal loading during lifting from an industrial bin. Two lifting styles and two bin design factors were examined in Phase I. The lifting style measures in Phase I were one hand versus two hand and standing on one foot versus two feet. The bin design variables were region of load in the bin and bin height. The Phase II study examined one-handed lifting styles with and without supporting body weight with the free hand on the bin as well as region and the number of feet. Twelve male and 12 female subjects lifted an 11.3 kg box from the bin. Spinal compression, lateral shear and anterior - posterior shear forces were estimated using a validated EMG-assisted biomechanical model. Phase I results indicated that the bin design factor of region had the greatest impact on spinal loading. The upper front region minimized spinal loading for all lifting styles. Furthermore, the lifting style of two hands and two feet minimized spinal loading. However, comparing Phase I two-handed lifting with Phase II one-handed supported lifting, the one-handed supported lifting techniques had lower compressive and anterior - posterior shear loads in the lower regions as well as the upper back region of the bin. A bin design that facilitates lifting from the upper front region of the bin reduces spinal loading more effectively than specific lifting styles. Furthermore, a bin design with a hand hold may facilitate workers using a supported lifting style that reduces spinal loading.     

Spinal loading when lifting from industrial storage bins

The study documented three-dimensional spinal loading during lifting from an industrial bin. Two lifting styles and two bin design factors were examined in Phase I. The lifting style measures in Phase I were one hand versus two hand and standing on one foot versus two feet. The bin design variables were region of load in the bin and bin height. The Phase II study examined one-handed lifting styles with and without supporting body weight with the free hand on the bin as well as region and the number of feet. Twelve male and 12 female subjects lifted an 11.3 kg box from the bin. Spinal compression, lateral shear and anterior - posterior shear forces were estimated using a validated EMG-assisted biomechanical model. Phase I results indicated that the bin design factor of region had the greatest impact on spinal loading. The upper front region minimized spinal loading for all lifting styles. Furthermore, the lifting style of two hands and two feet minimized spinal loading. However, comparing Phase I two-handed lifting with Phase II one-handed supported lifting, the one-handed supported lifting techniques had lower compressive and anterior - posterior shear loads in the lower regions as well as the upper back region of the bin. A bin design that facilitates lifting from the upper front region of the bin reduces spinal loading more effectively than specific lifting styles. Furthermore, a bin design with a hand hold may facilitate workers using a supported lifting style that reduces spinal loading.     

Manual materials handling capabilities in non-standard postures.

Research efforts to establish manual materials handling (MMH) capabilities of individuals and populations have been conducted for many years. Most of the previous efforts have explored 'standard postures', utilizing two-handed, symmetric, sagittal plane MMH using unrestricted postures. Recognizing that many industrial MMH activities do not utilize 'standard postures', recent research projects have explored psychophysically determined MMH capacities in a variety of non-standard postures. Among the non-standard postures examined were: twisting while lifting or lowering, lifting and lowering from lying, sitting, kneeling, and squatting positions, and carrying loads under conditions of constricted ceiling heights. This paper presents the results of a series of previous research efforts at Texas Tech University. The results are presented in the form of population capabilities of both males and females for 99 MMH tasks using 'non-standard postures'. The data tables contain means and standard deviations of the data, as well as percentile distributions for the subject populations. Sample sizes for the experimental populations ranged from 45 to 50 subjects of each sex in the first three experiments to 20 subjects of each sex in the fourth set of experiments.     

Two-handed assembly with immersive task planning in virtual reality

Assembly modelling is the process of capturing entities and activity information related to assembling and assembly. Currently, most CAD systems have been developed to ease the design of individual components, but are limited in their support for assembly designs and planning capability, which are crucial for reducing the cost and processing time in complex design, constraint analysis and assembly task planning. This paper presents a framework of a two-handed virtual assembly (VA) planner for assembly tasks, which coordinates two hands jointly for feature-based manipulation, assembly analysis and constraint-based task planning. Feature-based manipulation highlights the important assembling features (e.g. dynamic reference frames, moving arrow, mating features) to guide users for the ease of assembly and in an efficient and fluid manner. The users can freely navigate and move the mating pair along the collision-free path. The free motion of two-handed input in assembly is further restricted to the allowable motion guided by the constraints recognised on-line. The allowable motion in assembly is planned by the logic steps derived from the analysis of constraints and their translation in the progress of assembly. No preprocessing or predefined assembly sequence is necessary since the planning is produced in real-time upon the two-handed interactions. Mating features and constraints in databases are automatically updated after each assembly to simplify the planning process. The two-handed task planner has been developed and experimented for several assembly examples including a drill (12-parts) and a robot (17-parts). The system can be generally applied for the interactive task planning of assembly-type applications.     

Manual materials handling capabilities in non-standard postures

Research efforts to establish manual materials handling (MMH) capabilities of individuals and populations have been conducted for many years. Most of the previous efforts have explored ‘standard postures’, utilizing two-handed, symmetric, sagittal plane MMH using unrestricted postures. Recognizing that many industrial MMH activities do not utilize ‘standard postures’, recent research projects have explored psychophysicaly determined MMH capacities in a variety of non-standard postures. Among the non-standard postures examined were: twisting while lifting or lowering, lifting and lowering from lying, sitting, kneeling, and squatting positions, and carrying loads under conditions of constricted ceiling heights. This paper presents the results of a series of previous research efforts at Texas Tech University. The results are presented in the form of population capabilities of both males and females for 99 MMH tasks using ‘non-standard postures’. The data tables contain means and standard deviations of the data, as well as percentile distributions for the subject populations. Sample sizes for the experimental populations ranged from 45 to 50 subjects of each sex in the first three experiments to 20 subjects of each sex in the fourth set of experiments.     

A psychophysical study of high-frequency arm lifting

Ergonomics research on worker lifting in industry, and the many tools and methods that have resulted from it, have most often concentrated on the maximum amount of weight that a worker is capable and willing to lift in a given situation. In most psychophysical research on lifting, the frequency is one of a number of controlled variables along with container size, lift range, etc. Most of the relatively few studies that have investigated frequency as the response variable have used relatively heavy loads. In the study reported here, the focus was on the lifting of light weights and the subject acceptance of maximum frequency of lift for a two-handed lifting task. The lift range was set at approximately knuckle to shoulder height and was intended to simulate industrial jobs where the worker is tasked with either loading or unloading relatively light weight items to or from a processing line operation. Twelve college-age male subjects were used. Two conditions of weight, 0.7 kg (1.5 lb.) and 4.45 kg (10 lb.) were used and the subject adjusted his frequency of lift by communicating with the researcher, who adjusted a metronome to pace the task. The subjects were instructed to work at as fast a rate as they could for an hour period without becoming overheated, overly tired, out of breath or in pain. Measurements of oxygen consumption and heart rate were taken to supplement the psychophysical measure of lift frequency. Two replications of each weight condition were performed. At the conclusion of the metronome-paced sessions, an additional session for each weight condition was performed where the subject was instructed to lift as fast and consistently as they could with no external cuing device. The mean frequencies of lift identified in the experiment were 31.21 lifts per minute and 23.50 lifts per minute for the 0.7 kg and 4.5 kg lift weights respectively. The two weight conditions were significantly different from each other in their effects on subject metabolic energy expenditure with the subjects tending to work significantly harder physiologically at the heavier weight.     

The development of a model to predict the effects of worker and task factors on foot placements in manual material handling tasks

Accurate prediction of foot placements in relation to hand locations during manual materials handling tasks is critical for prospective biomechanical analysis. To address this need, the effects of lifting task conditions and anthropometric variables on foot placements were studied in a laboratory experiment. In total, 20 men and women performed two-handed object transfers that required them to walk to a shelf, lift an object from the shelf at waist height and carry the object to a variety of locations. Five different changes in the direction of progression following the object pickup were used, ranging from 45° to 180° relative to the approach direction. Object weights of 1.0 kg, 4.5 kg, 13.6 kg were used. Whole-body motions were recorded using a 3-D optical retro-reflective marker-based camera system. A new parametric system for describing foot placements, the Quantitative Transition Classification System, was developed to facilitate the parameterisation of foot placement data. Foot placements chosen by the subjects during the transfer tasks appeared to facilitate a change in the whole-body direction of progression, in addition to aiding in performing the lift. Further analysis revealed that five different stepping behaviours accounted for 71% of the stepping patterns observed. More specifically, the most frequently observed behaviour revealed that the orientation of the lead foot during the actual lifting task was primarily affected by the amount of turn angle required after the lift (R(2) = 0.53). One surprising result was that the object mass (scaled by participant body mass) was not found to significantly affect any of the individual step placement parameters. Regression models were developed to predict the most prevalent step placements and are included in this paper to facilitate more accurate human motion simulations and ergonomics analyses of manual material lifting tasks. STATEMENT OF RELEVANCE: This study proposes a method for parameterising the steps (foot placements) associated with manual material handling tasks. The influence of task conditions and subject anthropometry on the foot placements of the most frequently observed stepping pattern during a laboratory study is discussed. For prospective postural analyses conducted using digital human models, accurate prediction of the foot placements is critical to realistic postural analyses and improved biomechanical job evaluations.     

基于双手交互的指挥空间响应模型

自然高效的人机交互技术正快速发展,但双手交互技术和应用空间之间在认知上存在较大差距。使双手交互难以被广泛应用。该文对指挥空间进行认知级描述。根据指挥空间双手交互应用背景,按分布式认知和以用户为中心的思想构建一种基于双手交互的指挥空间交互响应模型。以解析的方式描述用户背景知识与交互响应间的关系,为指挥空间内双手交互的设计提供依据。     

双手交互界面研究进展

用户界面的发展趋势已经从“以技术为中心”发展为“以用户为中心”的新阶段,双手交互作为适应这种趋势的一种主要界面形式,以其自然直观等特点逐渐受到人们重视．系统地阐述了这种界面的研究现状,从双手操作的行为学和心理学基础出发,由实验评估总结出双手交互界面的基本设计准则,分类比较几种典型的交互技术,最后指出了存在的问题和下一步的研究方向．     

Relative role of merging and two-handed operation on command selection speed

This paper examines the influence of two interface characteristics on command selection speed: the integration of command selection with direct manipulation (merging), and two-handed operation. We compared four interaction techniques representing combinations of these characteristics (Marking Menu, Two-handed Tool Palette, Toolglass, and Control Menu). Results suggest that the one-handed techniques selected for the present study produced a speed advantage over two-handed techniques, whereas the influence of merging was task dependent. A follow-up study examining Bimanual Marking Menu suggests that the performance of two-handed techniques may be reduced due to a split in visual attention required for certain techniques. Taken together, these findings have important implications for the design of command selection mechanisms for pen-based interfaces.     

Investigating one-handed and two-handed inter-device interaction

Using a mobile device together with a large shared screen supports collaborative tasks and potentially prevents interference among users. In order to evaluate the usability of inter-device interaction, this paper compared two fundamental inter-device interaction styles, i.e., one-handed and two-handed interaction. The one-handed interaction style only uses one hand to select an object from a large display device while the two-handed interaction style needs the cooperation of two hands to realize a selection. A framework was developed to implement these two interaction styles. Based on the framework, a pretest-posttest, repeated-measures study was conducted to compare their differences. All participants went through eight tasks, which were differentiated by both the selection order (sequential or random order) and the density level (sparse or dense layout), using both interaction styles. During the study, both the completion time and the error rate in each task with each interaction style were recorded. In addition, the IBM Post-Study Usability Questionnaire (PSSUQ) was used to evaluate the subjective satisfaction on each interaction style. The overall PSSUQ score indicates that both interaction styles receive positive feedback with high user satisfaction. The study also revealed that the one-handed interaction took less time to complete tasks (i.e., more efficient) than the two-handed interaction, while the two-handed interaction style had a lower error rate than the one-handed interaction, and especially so in a dense layout.     

基于小波提升框架的图像序列中运动目标检测算法

图像序列中运动目标的检测和跟踪是智能监测系统中的重要问题，为了提高运动目标识别的效率和准确性，同时解决日标运动中的形变造成的检测困难，首先针对传统的运动日标检测算法所存在的局限．把小波提升框架运用到运动目标的检测中，然后充分利用小波的多分辨率特性和提升框架可以直接在时空域内设计的优点，再结合可变模板方法，提出了一种新的基于小波提升框架的运动目标检测算法。实验结果表明，新方法较好地解决了目标运动中因形变造成的检测困难，并提高了检测效率和速度。     

基于泛布尔代数的升船机结构逻辑控制研究

以抑制升船机结构的地震鞭梢效应为研究目标,根据升船机结构振动控制的相关经验,确立了泛布尔代数逻辑控制规则,完成了一种逻辑控制算法的设计。将该算法应用于现有的升船机结构模型的控制,成功运用Matlab/simulink进行了算法仿真,并对仿真结果进行了比较分析。仿真结果表明,基于泛布尔代数的逻辑控制方法控制简单、灵活、方便、有效,该逻辑控制算法适合典型的升船机结构,具有明显的抗震减震效果,达到了升船机结构抗震控制的工程要求。     

输入多采样率数字控制系统的同时极点配置

在利用提升(lifting)技术所构造出来的多采样率数字控制系统的线性时不变状态空间模型的基础上, 讨论l个被控对象通过输入多采样率数字控制系统的同时极点配置问题. 分别引入了解决这一问题的状态空间方法和多项式矩阵插值方法. 通过适当的变换, 将同时极点配置问题归结为一系列线性方程组的求解问题. 指出, 当系统的输入采样率满足一定条件时, 可以利用输入多采样率的输出静态反馈控制系统, 实现对l个被控对象的同时极点配置.     

The development of a model to predict the effects of worker and task factors on foot placements in manual material handling tasks

Accurate prediction of foot placements in relation to hand locations during manual materials handling tasks is critical for prospective biomechanical analysis. To address this need, the effects of lifting task conditions and anthropometric variables on foot placements were studied in a laboratory experiment. In total, 20 men and women performed two-handed object transfers that required them to walk to a shelf, lift an object from the shelf at waist height and carry the object to a variety of locations. Five different changes in the direction of progression following the object pickup were used, ranging from 45° to 180° relative to the approach direction. Object weights of 1.0 kg, 4.5 kg, 13.6 kg were used. Whole-body motions were recorded using a 3-D optical retro-reflective marker-based camera system. A new parametric system for describing foot placements, the Quantitative Transition Classification System, was developed to facilitate the parameterisation of foot placement data. Foot placements chosen by the subjects during the transfer tasks appeared to facilitate a change in the whole-body direction of progression, in addition to aiding in performing the lift. Further analysis revealed that five different stepping behaviours accounted for 71% of the stepping patterns observed. More specifically, the most frequently observed behaviour revealed that the orientation of the lead foot during the actual lifting task was primarily affected by the amount of turn angle required after the lift (R ² = 0.53). One surprising result was that the object mass (scaled by participant body mass) was not found to significantly affect any of the individual step placement parameters. Regression models were developed to predict the most prevalent step placements and are included in this paper to facilitate more accurate human motion simulations and ergonomics analyses of manual material lifting tasks.

Statement of Relevance: This study proposes a method for parameterising the steps (foot placements) associated with manual material handling tasks. The influence of task conditions and subject anthropometry on the foot placements of the most frequently observed stepping pattern during a laboratory study is discussed. For prospective postural analyses conducted using digital human models, accurate prediction of the foot placements is critical to realistic postural analyses and improved biomechanical job evaluations.     

The influence of precision requirements and cognitive challenges on upper extremity joint reaction forces,moments and muscle force estimates during prolonged repetitive lifting

Prolonged repetitive lifting is a whole-body exertion. Despite this, the roles and physical exposures of the upper extremities are frequently neglected. The influence of precision requirements and cognitive distractions on upper extremity responses when lifting was evaluated by quantifying several biomechanical upper extremity quantities. Nine participants completed four 30-min lifting tasks with and without simultaneous cognitive distractions and/or precision placement constraints. Specific metrics evaluated were joint reaction forces and moments (wrist, elbow and shoulder) and modelled shoulder muscle forces (38 defined shoulder muscle mechanical elements). The addition of a precision requirement increased several metrics by up to 43%, while the addition of the cognitive distraction task had minimal influence. Furthermore, several metrics decreased by up to 14% after the first 10 min of lifting, suggesting a temporal change of lifting strategy.