Asymmetric Tasks Research Articles

A7 重量物挙上時の体幹の回旋動作に対する骨盤回旋の役割(動作解析2・他)

A7 重量物挙上時の体幹の回旋動作に対する骨盤回旋の役割(動作解析2・他)

Delayed and bilateral changes of GAP-43/B-50 phosphorylation after circling training during a critical period in rat striatum

During the critical period of activity-dependent plasticity in rat striatum (30–37 days after birth) physiological circling behavior induces delayed modifications in GAP-43/B-50 phosphorylation by PKC. Postexercise, ipsi- and contralateral striatum to the circling direction show a similar temporal pattern of GAP-43/B-50 phosphorylation, with an initial decrease followed by a subsequent increase. However, there is a lag between initiation of the phosphorylation response in this asymmetrical task which does not occur when animals are subjected to exercise under conditions of symmetrical motor activity.

Integrative and Distributive Negotiation in Small Groups: Effects of Task Structure, Decision Rule, and Social Motive

This study examined the interactive effects of task structure, decision rule, and social motive on small-group negotiation processes and outcomes. Three-person groups negotiated either within an asymmetrical task structure (in which a majority of group members have compatible interests) or within a symmetrical task structure (in which no such majority exists). Groups negotiated either under unanimity rule or under majority rule, and group members were either egoistically or prosocially motivated. Results revealed cumulative main effects and the predicted three-way interaction: Groups in an asymmetrical task structure engaged in more distributive and less integrative behavior, reached lower joint outcomes, and experienced a less positive group climate especially when they had an egoistic rather than prosocial motivation and unanimity rather than majority rule applied. Theoretical implications and avenues for future research are discussed.

A biomechanical comparison of lifting techniques between subjects with and without chronic low back pain during freestyle lifting and lowering tasks

Objective. To evaluate if chronic low back pain patients perform manual material handling tasks differently from control subjects. Design. Comparative study using a repeated measures design. Background. No study evaluated the lifting technique of back pain patients relative to control subjects during free style lifting and lowering tasks. Previous findings suggest that lowering would be more hazardous than lifting to the low back. It would be interesting to evaluate if chronic low back pain patients behave differently than controls when lifting and lowering. Methods. Thirty-three male subjects (18 controls, 15 suffering from non-specific chronic low back pain) participated. A 12-kg box was lifted (freestyle) from the floor to the hips (1) in front (symmetric task) or (2) to a shelf located at 90° on the right (asymmetric task) and was lowered back to the floor. A 3D biomechanical analysis involving the assessment of L5/S1 loading, posture of segments, inertial parameters, and EMG was performed. Results. There was no difference between the groups for postural (trunk and lower limb angles), inertial (trunk velocity and acceleration), and L5/S1 loading (moments and compression) variables. The patients showed abnormally low left lumbar erector spinae (symmetric task, lowering) or high left thoracic erector spinae (all tasks) EMG activation. Significant Group×Action (lifting vs lowering) interactions were also observed for some inertial and L5/S1 loading variables suggesting that the biomechanical differences detected between lifting and lowering may have a differential influence on the technique used by back pain patients and control subjects. Conclusions. The gross lifting technique of back pain patients was unaltered relative to controls but the activation of paraspinal muscles differed, suggesting that a more detailed biomechanical analysis, such as the use of EMG driven models, might be required to reveal lumbar impairments during lifting. Relevance To evaluate if chronic low back pain patients use naturally different lifting techniques to prevent pain exacerbation and damaged lumbar tissue overloading.

Dynamic loads on the upper extremities during two different floor cleaning methods

Background. Biomechanical models have been used frequently to estimate the load on the low back and the lower extremities during occupational work tasks. The shoulder region has received much less attention although this area is a common site of work-related musculoskeletal disorders. Objective. The aim of the present study was to evaluate the mechanical loading of the upper extremities during floor cleaning performed with different techniques. Design. A comparative study of six subjects performing floor cleaning with two different techniques (mopping and scrubbing) in a laboratory setting. Methods. A “force handle” equipped with two force dynamometers was used for continuous measurement of three-dimensional forces on each hand, separately, during this two handed asymmetrical task. A link segment model of the upper extremities was used to calculate the mechanical loading of the elbows and shoulders. Electromyograms were recorded from six shoulder muscles. Results. Despite differences in movement patterns between mopping and scrubbing, only small differences were found in the moments of force. In accordance similar levels of electromyograms were found. Conclusion. In preventive strategies, changing the cleaning tool may not be sufficient to change the load on the shoulder muscles. Relevance Combined three-dimensional video recording and force measurements on the hands during a two-handed asymmetric work tasks allow calculation of the mechanical load on the elbow and shoulder. Thus it is possible to evaluate physiologically, new equipment designed to prevent work-related musculoskeletal disorders. Before introducing such equipment in large scale interventions it may be evaluated if the changes in force requirements are sufficient to predict prevention of musculoskeletal disorders.

Bilateral deficit and symmetry in finger force production during two-hand multifinger tasks.

A comprehensive study of patterns of finger forces during one-hand and two-hand multifinger maximal force production trials was performed with particular emphasis on differences between tasks involving symmetrical and asymmetrical finger groups (symmetrical and asymmetrical tasks). Twelve healthy right-handed subjects performed maximal voluntary force production tasks with different finger combinations. Force deficit (FD) for a finger group within a hand was defined as a drop in peak force in a multifinger task as compared to the sum of individual finger peak forces in single-finger tasks. FD showed a dependence on both the number of fingers within the hand and the number of fingers in the other hand. An additional drop in peak finger forces was seen in two-hand tests (bilateral deficit, BD). BD summed over two hands was independent of the number of fingers involved in the two-hand tasks, but dependent on the distribution of fingers between the two hands. BD for a hand was larger for tasks involving fewer fingers within the hand and more fingers in the other hand. It was higher for asymmetrical tasks than for symmetrical tasks. The difference between asymmetrical and symmetrical tasks was due to the different behavior of asymmetrically involved fingers. FD was larger for asymmetrical master (explicitly involved) fingers, while forces produced involuntarily by asymmetrical slave (explicitly non-involved) fingers were larger. These differences brought down the total moment produced by both hands in the frontal plane. FD and BD are phenomena of different origin whose effects sum up. The observations have led to further development of a previously proposed double-representation, mirror-image (DoReMi) hypothesis and refinement of the neural network underlying the two-hand finger interaction.

Interaction of Physical and Mental Workplace Stressors: Their Impact on Spinal Loads

For the first time, this study investigated how individuals react to both physical and mental workplace factors and how these reactions impact the loads on the spine. Thirty males and thirty females performed asymmetric lifting tasks at two different lift rates (2 and 8 lifts/min) and accompanied by two levels of mental concentration demands (none and keyboard entry task). Three-dimensional spinal loads were found to be greater for the faster lift rate and highest when mental concentration accompanied the fastest lift rate. Individuals responded to increases in lifting rates and mental demands by altering their trunk and hip motions as well as produced greater muscle coactivity. Thus, how an individual performs a particular lifting tasks is dependent upon both the physical requirements of the job but also the mental aspects. Workplace stressors that have the ability to influence the time pressures on the individuals have the potential to significantly influence the biomechanical responses and ultimately the loads on the spine.

Back muscle contraction patterns of patients with low back pain before and after rehabilitation treatment: an electromyographic evaluation.

The aims of this study were to conduct a comparative investigation of muscle function between patients with low back pain (LBP) and healthy persons, and to determine whether intensive rehabilitation can change back muscle contraction synergy. Twenty healthy persons and 20 patients with chronic LBP were asked to perform symmetrical and asymmetric tasks. The patients with LBP were tested in the weeks immediately before and after 12 weeks of LBP rehabilitation. Tasks include "carrying" weights up and down and with a 45 degrees left rotation. Eight-channel surface electromyographic electrodes were placed on the surface of paraspinal muscles over the lumbar region. Correlations between the right and left corresponding muscles and between values before and after treatment were determined. Lifting capacity for patients with LBP were also measured before and after treatment. Results from electromyographic profiles showed that the muscle activity strategies varied between healthy persons and patients with LBP. The correlation coefficients for spinal muscles have shown very reproducible intrasubject muscle contraction synergies. Unbalanced electromyographic patterns found in patients with LBP given symmetrical tasks were not affected by rehabilitation treatment.

Finger Coordination and Bilateral Deficit during Two-Hand Force Production Tasks Performed by Right-Handed Subjects

One purpose of the present study was to compare indices of finger coordination during force production by the fingers of the right hand and of the left hand. The other purpose was to study the relation between the phenomena of force deficit during multifinger one-hand tasks and of bilateral force deficit during two-hand tasks. Thirteen healthy right-handed subjects performed maximal voluntary force production tasks with different finger combinations involving fingers of one hand or of both hands together. Fingers of the left hand demonstrated lower peak forces, higher indices of finger enslaving, and similar indices of force deficit. Significant bilateral effects during force production by fingers of both hands acting in parallel were seen only during tasks involving different fingers or finger groups in the two hands (asymmetrical tasks). The bilateral deficit effects were more pronounced in the hand whose fingers generated higher forces. These findings suggest a generalization of an earlier introduced principle of minimization of secondary moments. They also may be interpreted as suggesting that bilateral force deficit is task-specific and may reflect certain optimization principles.

Motivated Impressions of a Powerholder: Accuracy Under Task Dependency and Misperception Under Evaluation Dependency

Two experiments assessed the impression-formation strategies used by asymmetrically dependent (powerless) people to form impressions of powerholders. The experiments contrast two types of asymmetrical dependency: task dependency (short-term, goal-oriented outcome contingency) and evaluation dependency (expecting evaluations of one’s performance or abilities). Experiment 1 hypothesized and found that asymmetrical task dependency increases accuracy-driven impression-formation processes: Task-dependent people attend to information that disconfirms initial expectancies about a powerholder and, if asymmetrical, do not discount trait information. Experiment 2 found that evaluation dependency increases motivated misperception to view the powerholder positively. Evaluation-dependent people attend to and then discount negative information, which is reflected in their ratings of a powerholder.

Effects of Trunk Muscle Fatigue on Spine Mechanics during Repetitive Asymmetrical Lifting

The purpose of this study was to determine the effects of repetitive lifting on trunk muscle activity and spine kinematics during an intense, forty minute, asymmetrical lifting and lowering task. Contrary to many previous sagittal plane materials handling studies, the asymmetrical task did result in differences in kinematics between lifting and lowering. Further, there were few consistent effects of fatigue on trunk muscle activity and only spine flexion was observed to decrease over the course of the trials. However, some individual subjects did demonstrate fatigue related changes that may have increased their risk of injury if performed over prolonged periods.

A Comparison of Males and Females during Asymmetric Lifting

This study evaluated the differences in spinal loading between males and females while performing complex free-dynamic whole body lifts. Twenty males and twenty-five females performed sagittally symmetric and asymmetric lifting tasks from mid-shin and knee height origins. Only minor differences between males and females were found in three-dimensional spinal loads. The compressive loads for the females appeared to be independent of the experimental condition (e.g. lifting task or velocity). Females adopted a different kinematic pattern compared to males as well as recruited more antagonistic muscles when performing similar tasks. When spinal tolerance differences are considered, females would be expected to be more at risk of injury during typical lifting tasks.

Variability and correlations in bi-manual pointing movements

Bi-manual movement tasks present us with an intriguing paradox: on one hand it is clear that we are capable of controlling our hands independently, yet at the same time we often notice that one hand influences the other. We investigated bi-manual pointing movement towards a common target and hypothesised that if (parts of) bi-manual movements are planned as one functional unit, then there should be significant correlations between the movement parameters of each hand. Surprisingly, we found only consistently high correlation coefficients with regard to the reaction time. Our results demonstrate that trajectory formation and adjustments of bi-manual movements are largely independent and hand-specific, contradicting the notion that the left and right hand are controlled as one functional unit. Because we find that average, rather than individual, movements are correlated, we conclude that coupling between the two hands occurs only at `task level'. In symmetrical tasks, movements are initiated simultaneously. In asymmetrical tasks, however, there are small but very consistent timing differences between the left and right hands. These differences are small compared to the variability in reaction times and, therefore, we conclude that they result from an intrinsic control property of the system of bi-manual movement generation. PsycINFO classification: 2330; 2520

Assessment of an EMG-based method for continuous estimates of low back compression during asymmetrical occupational tasks

Variables, such as peak and accumulated moments and spine compression forces, have been shown to be risk factors for occupational low back pain. Estimates of these forces during prolonged, dynamic, asymmetric tasks using biomechanical models is complex and time-consuming. A simple technique for continuous measurement of these variables over a prolonged period is needed to measure the distribution of spinal loading during both sagittal plane lifts and complex asymmetrical jobs. The aim of this study was to determine whether a linear normalization of erector spinae EMG to spine compression force, called compression normalized EMG (CNEMG), could be used to estimate spinal loading for simulations of asymmetrical occupational tasks. The estimates of spine compression force obtained using the normalized EMG are presented in the form of an amplitude probability distribution function and are compared with estimates of a three-dimensional biomechanical model. The per cent time a worker spends above particular levels of spinal loading of interest, such as the NIOSH action limit for compression, are displayed. Five males performed simulated occupational tasks. The exposure time at a specific level of spine compression force for a combination of three tasks, estimated by CNEMG, was, on average, within 6.5% of the time calculated by the biomechanical model. However, if the task combination was dominated by an axial twisting moment, then the difference was, on average, 13.4%. The difference in magnitude of spine compression at a specific probability was, on average, 14.9% and when axial trunk twist dominated, 30.7%. It is concluded that CNEMG can estimate probability at a specific level of spine compression force when the task combination is characterized by a predominant extensor moment in the sagittal plane. Estimates of spine compression at a specific probability, and estimates obtained during task combinations dominated by an axial twisting moment, are poor.

The effects of lifting speed on the peak external forward bending, lateral bending, and twisting spine moments

Lifting tasks that involve twisting have been repeatedly implicated as contributing to the onset of occupational back injuries in epidemiological studies. The objective of this work was to quantify the three directional external moments acting on the spine during a sagittally symmetric and two asymmetric lifting tasks. A total of 15 subjects participated in the three lifting tasks. All tasks were performed at two qualitatively defined lifting speeds, ‘slow’ and ‘fast’, and with two load magnitudes: 10 and 20% of the subject's body weight. The mid-sagittal plane lifts were performed using two horizontal reach distances: 40 and 60 cm. A four-camera, two-forceplate motion and force measurement system were used to obtain the kinematic and kinetic data as the lifts were performed. A dynamic linksegment biomechanical model was used to quantify the reaction forces and moments at the ankle, knee, and hip and L5/S1 joints. Results from all tasks showed increased sagittal plane (forward bending) spine moments with the heavier load and at the faster lifting speed (p < 0.001). Spine lateral bending and twisting moments increased during the mid-sagittal plane lifts with the greater reach distance and the faster lifting speed, respectively. The twisting moments on the spine were greatest as subjects lifted from in front and placed the load to the side but were dependent upon the lifting speed and the load magnitude. The lateral bending moments increased during this same task with the heavier load. However, the spine lateral bending moments were greatest when lifting from one side to the other.

Instability of torsion during smooth asymmetric vergence.

Several categories of torsional eye movements obey Listing's law; however, systematic deviations from this law occur during vergence. Two kinematic models attempt to incorporate these deviations, both of which are supported by experimental evidence; however, they lead to different torsion predictions. These discrepancies have been explained in terms of experimental procedures, but it now seems likely from several recent studies that individual differences in torsion patterns may also be important. This study therefore examines the variation of torsion during a smooth asymmetric vergence task in which a fixation target was moved along the line-of-sight of the right eye at 15 degrees elevation; each of five subjects observed five trials of both inward and outward target motion, repeated in two sessions several weeks apart. There were no significant group differences in left or right eye torsion between trials or sessions, suggesting that monocular torsion patterns were relatively stable over time. When examined more closely, however, the torsion patterns shown by some individuals did vary for inward versus outward target motion. Hence, monocular torsion was idiosyncratic and depended on the direction in which fixation was changing (convergence or divergence). In a binocular analysis, cycloversion varied dramatically between subjects and depended on the direction of target motion; however, this was not the case for cyclovergence. In summary, cyclovergence is relatively stable and depends on where the eyes are looking, whereas cycloversion (and hence monocular torsion) is relatively unstable and depends on how they came to be in that particular horizontal and vertical orientation. These findings help to explain the controversy surrounding the torsional behaviour of the human eye during vergence.

Three dimensional moments in the lumbar spine during asymmetric lifting

Objective. To better understand the loads placed on the spine during asymmetric lifting. Design. Analysis of variance was used to test the effects of asymmetry (0, 45, 90 °), event (up, down, min and max), and trial (first and second) on applied spine moments and resulting EMG signals in the lumbar spine. Background. Loading conditions resulting from symmetric lifting are well documented in the literature, yet free-style asymmetric tasks have not been intensively studied. Methods. Infrared markers and EMG electrodes were fixed to ten subjects. Subjects were asked to lift a 45 N weight from three different positions in relation to the sagittal plane. External loads on the L3-L4 and L4-L5 disc planes were calculated. Maximum moments and EMG were compared with those at lift off and set down of the burden. All lifts were repeated twice. Results. Introducing asymmetry to the lift increased lateral bending and twisting moments. Flexion moments increased by approximately 5% after lift off of the load. During the second repetition of the lift, flexion and twisting moments decreased and increased, respectively. EMG signals were greater on the contralateral side during asymmetric lifts. Conclusions. Asymmetric lifting places complex loads across the trunk, which may become increasingly asymmetric with repeated trials.

The effect of complex dynamic lifting and lowering characteristics on trunk muscles recruitment

A better understanding of how the neuromuscular spinal system behaves during lifting and lowering could provide more insight about potential causes of occupational low back disorders (LBDs), and could help in the prevention and rehabilitation process of these disorders. The purpose of this study was to quantify trunk muscle activities under various whole-body free-dynamic symmetric and asymmetric complex lifting and lowering tasks. Eleven male subjects with no prior history of LBDs participated in the study. Electromyographic activities of ten trunk muscles were monitored while subjects either symmetrically or asymmetrically lifted and lowered a box under three different speeds and three weights. The results showed that all ten muscles were responsive to various experimental conditions with the erector spinae and internal oblique muscles showing the greatest response. Substantial electromyographic activities were observed in muscles that were on the contralateral side of the load. Lowering conditions yielded consistently lower muscular activities than their corresponding lifting conditions. These results show that it is essential to consider multiple trunk muscles in modeling efforts of quantifying spinal loading, as well as for back rehabilitation research purposes.

Effects of body posture, weight and frequency on time-dependent muscle strengths during dynamic materials handling tasks

We examined the effects of body posture, weight and frequency on time-dependent muscle strengths during dynamic materials handling tasks. Maximum voluntary isometric strengths (MVIS) of nine healthy males were evaluated for symmetric and asymmetric postures, respectively, and their time-dependent muscle strengths were measured after performing 2 hours of lifting and lowering tasks with varying conditions. The percentage decrease in normalized MVIS after performing each task was then reported. The mean MVIS across the subjects for the asymmetric posture of 90° lateral plane to the right was significantly lower than that for the symmetric posture. The percentage decrease in MVIS after performing the asymmetric tasks was found to be significantly greater than that for the symmetric tasks. A correction factor of 34.1% is recommended to modify the sagittally symmetric MVIS data when they are utilized in the asymmetric posture of 90°. Furthermore, the MVIS data should be adjusted by 13.4% and 24.2% for durations of 2 hours for symmetric and asymmetric tasks, respectively.

Validation of two 3-D segment models to calculate the net reaction forces and moments at the [formula omitted] joint in lifting

The purpose of this study was to examine the validity and sensitivity of two three-dimensional segment models to estimate the net reaction forces and moments at the L 5 S 1 joint. The two dynamic three-dimensional multisegment models, applied to lifting activities, were a lower body model and an upper body model. Three healthy male subjects participated in this study. The asymmetrical task consisted of lifting a load of 9.6 kg in a normal speed condition and in a fast condition. Results from the two models in terms of joint reaction forces and joint reaction moments at L 5 S 1 were compared and were then used to validate them. The correlation between the reaction moments from both models were generally above 0.95 and the root mean square (RMS) differences were generally below 10 Nm but could reach 38 Nm. Similar trends were observed in the sensitivity analysis. A proportion of the error was attributable to errors in the segment accelerations because of an increase in the RMS differences between the models with an increase in lifting speed. The use of the lower body model seemed to present some advantages over the upper body model because of the nature of the task analysed which did not require large accelerations from the lower part of the body.