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- Madeleine, Pascal, et al.
(författare)
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Changes in the degree of motor variability associated with experimental and chronic neck-shoulder pain during a standardised repetitive arm movement
- 2008
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Ingår i: Experimental Brain Research. - : Springer Science and Business Media LLC. - 0014-4819 .- 1432-1106. ; 185:4, s. 689-698
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to investigate the effect of experimental and chronic neck-shoulder pain on the magnitude of cycle-to-cycle variability of task timing, kinematics and muscle activation during repetitive arm movement performed for 3 or 5 min. In an experimental part, acute muscle pain was induced in healthy subjects by intramuscular injection of hypertonic saline in trapezius (n = 10) and infraspinatus (n = 10) muscles. In a clinical part, workers with (n = 12) and without (n = 6) chronic neck-shoulder pain were compared. Cycle-to-cycle standard deviations of task duration, arm and trunk movement in 3D and surface electromyographic (EMG) root mean square activity were computed to assess the degree of variability. The variability in task timing increased in presence of both experimental and chronic pain (P < 0.05) compared with non-painful conditions. Experimental pain increased the variability of the starting position of the arm (P < 0.05), the arm range of motion (P < 0.01), the arm and trunk movement area (P < 0.01) and the acceleration of the arm (P < 0.01). In the chronic pain condition, the variability of arm and trunk acceleration (P < 0.01) and EMG activity (P < 0.05) was decreased compared with healthy controls. These results indicate that pain alters the magnitude of motor variability, and that the transition from acute to chronic pain is accompanied by changes in motor patterns. Experimental pain likely resulted in a quest for a motor solution reducing nociceptive influx, while chronic pain was characterised by a diminished motor flexibility.
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| 2. |
- Madeleine, Pascal, et al.
(författare)
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The size of cycle-to-cycle variability in biomechanical exposure among butchers performing a standardized cutting task
- 2008
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Ingår i: Ergonomics. - : Informa UK Limited. - 0014-0139 .- 1366-5847. ; 51:7, s. 1078-1095
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Tidskriftsartikel (refereegranskat)abstract
- The effects of employment duration and pain development on motor variability were investigated during repetitive work. EMG and kinematics data from two previous studies were reanalyzed. Newly employed butchers were followed prospectively in relation to employment duration and pain development. Healthy butchers with long-term experience were compared with novices. The variability of the cycle time, EMG ratio, and arm and trunk movement was expressed as cycle-to-cycle standard deviations. During the first six months of employment, cycle time variability decreased, while posture and movement variability increased (P<0.05). In presence of pain, the variability of the initial arm position decreased while it increased for the trunk (P<0.05). Experienced butchers showed a larger variability than novices for work cycle and several kinematic variables, but a smaller EMG ratio variability (P<0.05). These findings indicate that the variability of motor patterns in repetitive work change with experience and pain. A change towards a more variable motor strategy may protect workers from work-related musculoskeletal disorders.
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| 6. |
- Samani, Afshin, et al.
(författare)
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Cluster-based exposure variation analysis
- 2013
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Ingår i: BMC Medical Research Methodology. - : Springer Science and Business Media LLC. - 1471-2288. ; 13, s. 54-54
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Tidskriftsartikel (refereegranskat)abstract
- Background: Static posture, repetitive movements and lack of physical variation are known risk factors for work-related musculoskeletal disorders, and thus needs to be properly assessed in occupational studies. The aims of this study were (i) to investigate the effectiveness of a conventional exposure variation analysis (EVA) in discriminating exposure time lines and (ii) to compare it with a new cluster-based method for analysis of exposure variation.Methods: For this purpose, we simulated a repeated cyclic exposure varying within each cycle between “low” and “high” exposure levels in a “near” or “far” range, and with “low” or “high” velocities (exposure change rates). The duration of each cycle was also manipulated by selecting a “small” or “large” standard deviation of the cycle time. Theses parameters reflected three dimensions of exposure variation, i.e. range, frequency and temporal similarity. Each simulation trace included two realizations of 100 concatenated cycles with either low (r=0.1), medium (r=0.5) or high (r=0.9) correlation between the realizations. These traces were analyzed by conventional EVA, and a novel cluster-based EVA (C-EVA). Principal component analysis (PCA) was applied on the marginal distributions of 1) the EVA of each of the realizations (univariate approach), 2) a combination of the EVA of both realizations (multivariate approach) and 3) C-EVA. The least number of principal components describing more than 90% of variability in each case was selected and the projection of marginal distributions along the selected principal component was calculated. A linear classifier was then applied to these projections to discriminate between the simulated exposure patterns, and the accuracy of classified realizations was determined.Results: C-EVA classified exposures more correctly than uni 1 variate and multivariate EVA approaches; classification accuracy was 49%, 47% and 52% for EVA (univariate and multivariate), and C-EVA, respectively (p<0.001). All three methods performed poorly in discriminating exposure patterns differing with respect to the variability in cycle time duration.Conclusion: While C-EVA had a higher accuracy than conventional EVA, both failed to detect differences in temporal similarity. The data-driven optimality of data reduction and the capability of handling multiple exposure time lines in a single analysis are the advantages of the C-EVA.
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| 7. |
- Samani, Afshin, et al.
(författare)
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Nonlinear metrics assessing motor variability in a standardized pipetting task : Between- and within-subject variance components
- 2015
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Ingår i: Journal of Electromyography & Kinesiology. - : Elsevier BV. - 1050-6411 .- 1873-5711. ; 25:3, s. 557-564
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to estimate the between days test-retest reliability of nonlinear metrics used to quantify motor variability in a repetitive precision task. On three separate days, 14 healthy subjects performed pipetting as a general model of repetitive precision tasks. The task consisted of transferring liquid 20 times with a cycle time of 2.8 s from a pickup tube to eight target tubes placed on a table in front of the subjects. The motion of hand, arm and the pipet tip was tracked in 3D and the shoulder elevation and elbow flexion angle were obtained. Motor variability was assessed using nonlinear metrics based on information theory and recurrence quantification analysis. Between- and within- (between-days) subject variance components were computed using a one-way random effect model, and intra-class correlation coefficients (ICC) were calculated from the variance components as standardized measures of reliability. Most of the metrics displayed a considerable between-days variance component and therefore the ICC showed a slight to moderate reliability. The reported data on between- and within-subject variability can be used to design future studies using non-linear motor variability metrics on kinematics data.
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| 8. |
- Samani, Afshin, et al.
(författare)
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Variability in patterns of muscular activity during a fatiguing repetitive task
- 2016
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Konferensbidrag (refereegranskat)abstract
- Background. Muscle fatigue develops at markedly different rates among individuals. The pattern of variation in muscle activity has been suggested as a determinant of the rate of fatigue development. This variation can occur between muscles or between compart-ments of a muscle. Thus, we investigated the pattern of muscular activity in shoulder and arm regions during a fatiguing repetitive work task.Methods. 21 healthy young women performed a repetitive pipetting task at 2.8 seconds/cycle. The session continued until the subject rate of perceived exertion reached 8 on Borg CR-10 scale. High density (HD) surface electromyogram (EMG) over upper trapezius, and bipolar EMG from extensor carpi radialis, flexor carpi radialis, biceps, triceps, deltoi-deus anterior, serratus anterior, upper and lower trapezius were collected to investigate intra- and inter-muscle variation patterns. EMG amplitude and mean power frequency (MPF) were obtained for all the recorded EMG signals. The barycenter of activity over the HD-EMG grid was also determined. Normalized mutual information (NMI) was determined for each pair of muscles. The extent of variability of the outcomes was also assessed.Results. As fatigue developed, EMG amplitude increased and the MPF decreased for all muscles except the MPF for upper trapezius and deltoideus. The activity of trapezius was higher on the lateral side of HD-EMG grid than on the medial side and the barycenter showed a lateral shift across time. NMI between the muscle pairs also increased with fatigue. The variability of the investigated outcomes was not associated with the time to the task ending.Discussion. Myo-electrical manifestations of muscle fatigue were observed but none of the outcomes had an association with the rate of fatigue development. Using multivariate approaches, synergistic pattern of muscular activity is yet to be investigated.
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| 9. |
- Samani, Afshin, et al.
(författare)
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Variability in spatio-temporal pattern of trapezius activity and coordination of hand-arm muscles during a sustained repetitive dynamic task
- 2017
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Ingår i: Experimental Brain Research. - : Springer Science and Business Media LLC. - 0014-4819 .- 1432-1106. ; 235:2, s. 389-400
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Tidskriftsartikel (refereegranskat)abstract
- The spatio-temporal distribution of muscle activity has been suggested to be a determinant of fatigue development. Pursuing this hypothesis, we investigated the pattern of muscular activity in the shoulder and arm during a repetitive dynamic task performed until participants' rating of perceived exertion reached 8 on Borg's CR-10 scale. We collected high density surface electromyogram (HD-EMG) over the upper trapezius, as well as bipolar EMG from biceps brachii, triceps brachii, deltoideus anterior, serratus anterior, upper and lower trapezius from 21 healthy women. Root mean square (RMS) and mean power frequency (MNF) were calculated for all EMG signals. The barycenter of RMS values over the HD-EMG grid was also determined, as well as normalized mutual information (NMI) for each pair of muscles. Cycle-to-cycle variability of these metrics was also assessed. With time, EMG RMS increased for most of the muscles, and MNF decreased. Trapezius activity became higher on the lateral side than on the medial side of the HD-EMG grid and the barycenter moved in a lateral direction. NMI between muscle pairs increased with time while its variability decreased. The variability of the metrics during the initial 10% of task performance was not associated with the time to task termination. Our results suggest that the considerable variability in force and posture contained in the dynamic task per se masks any possible effects of differences between subjects in initial motor variability on the rate of fatigue development.
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| 10. |
- Srinivasan, Divya, et al.
(författare)
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Effects of concurrent physical and cognitive demands on arm movement kinematics in a repetitive upper-extremity precision task
- 2015
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Ingår i: Human Movement Science. - : Elsevier. - 0167-9457 .- 1872-7646. ; 42, s. 89-99
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Tidskriftsartikel (refereegranskat)abstract
- The effect of concurrent physical and cognitive demands on arm motor control is poorly understood. This exploratory study compared movement kinematics in a repetitive high-precision pipetting task with and without additional concurrent cognitive demands in the form of instructions necessary to locate the correct target tube. Thirty-five healthy female subjects performed a standardized pipetting task, transferring liquid repeatedly from one pick-up tube to different target tubes. In the reference condition, lights indicated the target tube in each movement cycle, while the target tube had to be deciphered from a row and column number on a computer screen in the condition with additional cognitive demands. Kinematics of the dominant arm was assessed using the central tendency and variability of the pipette-tip end-point trajectory and joint kinematics properties of the shoulder and elbow. Movements slowed down (lower velocities and higher area under the movement curves) and end point trajectory variability increased in the condition with additional cognitive demands, but there were no changes in the kinematics properties such as joint range of motion, times of acceleration and deceleration (as indicated by the time to peak velocity), average angles, or phase relationships between angle and angular velocity of shoulder or elbow movements between the two conditions. Further, there were also no differences in the size or structure of variability of the shoulder and elbow joint angles, suggesting that subjects could maintain the motor repertoire unaltered in the presence of these specific additional cognitive demands. Further studies should address motor control at other levels of concurrent cognitive demands, and with motor tasks that are less automated than the pipetting task used in the present study, so as to gain an increased understanding of the effect of concurrent cognitive demands for other activities of relevance to daily life.
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