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  • 1.
    Domkin, Dmitry
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Forsman, Mikael
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden.
    Richter, Hans
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Ciliary muscle contraction force and trapezius muscle activity during manual tracking of a moving visual target2016Inngår i: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 28, s. 193-198Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Previous studies have shown an association of visual demands during near work and increased activity of the trapezius muscle. Those studies were conducted under stationary postural conditions with fixed gaze and artificial visual load. The present study investigated the relationship between ciliary muscle contraction force and trapezius muscle activity across individuals during performance of a natural dynamic motor task under free gaze conditions. Participants (N = 11) tracked a moving visual target with a digital pen on a computer screen. Tracking performance, eye refraction and trapezius muscle activity were continuously measured. Ciliary muscle contraction force was computed from eye accommodative response. There was a significant Pearson correlation between ciliary muscle contraction force and trapezius muscle activity on the tracking side (0.78, p < 0.01) and passive side (0.64, p < 0.05). The study supports the hypothesis that high visual demands, leading to an increased ciliary muscle contraction during continuous eye–hand coordination, may increase trapezius muscle tension and thus contribute to the development of musculoskeletal complaints in the neck–shoulder area. Further experimental studies are required to clarify whether the relationship is valid within each individual or may represent a general personal trait, when individuals with higher eye accommodative response tend to have higher trapezius muscle activity.

  • 2.
    Hansson, Gert-Åke
    et al.
    Department of Occupational and Environmental Medicine, University Hospital, Lund, Sweden.
    Arvidsson, Inger
    Department of Occupational and Environmental Medicine, University Hospital, Lund, Sweden.
    Ohlsson, Kerstina
    Department of Occupational and Environmental Medicine, University Hospital, Lund, Sweden.
    Nordander, Catarina
    Department of Occupational and Environmental Medicine, University Hospital, Lund, Sweden.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Centrum för belastningsskadeforskning. Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap.
    Skerfving, Staffan
    Department of Occupational and Environmental Medicine, University Hospital, Lund, Sweden.
    Balogh, Istvan
    Department of Occupational and Environmental Medicine, University Hospital, Lund, Sweden.
    Precision of measurements of physical workload during standardised manual handling: Part II : Inclinometry of head, upper back, neck and upper arms2006Inngår i: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 16, nr 2, s. 125-136Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For measuring the physical exposure/workload in studies of work-related musculoskeletal disorders, direct measurements are valuable. However, the between-days and between-subjects variability, as well as the precision of the method per se, are not well known. In a laboratory, six women performed three standardised assembly tasks, all of them repeated on three different days. Triaxial inclinometers were applied to the head, upper back and upper arms. Between-days (within subjects) and between-subjects (within tasks) variance components were derived for the 10th, 50th and 90th percentiles of the angular and the angular velocity distributions, and for the proportion of time spent in predefined angular sectors. For percentiles of the angular distributions, the average between-days variability was 3.4 degrees , and the between-subjects variability 4.0 degrees . For proportion of time spent in angular sectors, the variability depended on the percentage of time spent in the sector; the relative variability was scattered and large, on average 103% between days and 56% between subjects. For the angular velocity percentiles, the average between-days variability was 7.9%, and the average between-subjects variability was 22%. The contribution of the measurement procedure per se to the between-days variability, i.e., the imprecision of the method, was small: less than 2 degrees for angles and 3% for angular velocity.

  • 3.
    Jackson, Jennie A.
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Callaghan, Jack
    Department of Kinesiology, University of Waterloo, Ontario, Canada.
    Dempsey, Patrick
    National Institute for Occupational Safety and Health, Pittsburgh, USA.
    Precision based guidelines for sub-maximal normalisation task selection for trunk extensor EMG2017Inngår i: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 37, s. 41-51Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aim: The object of this study was to quantify the contribution of sub-maximal normalisation to the overall variance of exposure parameters describing erector spinae (ES) activity, and to provide guidelines for task selection which minimize methodological variance. Methods: ES EMG was measured from three locations (T9, L1 and L5 levels) on fifteen men performing a manual materials handling task in the laboratory on three separate days. Four repeats of each of eleven sub-maximal normalisation tasks (eight static, three dynamic) were collected, work data were normalised to each task and repeat, and exposure parameters calculated. The unique contribution of normalisation to the overall variance was determined for each task and exposure parameter using variance component analyses. Normalisation tasks were scored according to their relative contributions to the overall variance and coefficients of variation.

    Results: A prone task, similar to the Biering-Sørensen test posture, was the most repeatable for all electrode locations and across all exposure parameters. Thoracic level normalisation typically showed poorer repeatability than lumbar normalisation.

    Discussion: We recommend that future ES EMG studies employing sub-maximal normalisation utilise said prone task. An alternate normalisation task specific to thoracic level ES muscles may be warranted.

  • 4.
    Jackson, Jennie A
    et al.
    Högskolan i Gävle, Centrum för belastningsskadeforskning. Department of Kinesiology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada ; Liberty Mutual Research Institute for Safety, Hopkinton, USA.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Dempsey, Patrick G.
    Liberty Mutual Research Institute for Safety, Hopkinton, USA.
    Methodological variance associated with normalization of occupational upper trapezius EMG using submaximal reference contractions2009Inngår i: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 19, nr 3, s. 416-427Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives: To quantify the variance introduced to trapezius electromyography (EMG) through normalization by submaximal reference voluntary exertions (RVE), and to investigate the effect of increased normalization efforts as compared to other changes in data collection strategy on the precision of occupational EMG estimates. Methods: Women performed four RVE contractions followed by 30 minutes of light, cyclic assembly work on each of two days. Work cycle EMG was normalized to each of the RVE trials and seven exposure parameters calculated. The proportions of exposure variance attributable to subject, day within subject, and cycle and normalization trial within day were determined. Using this data, the effect on the precision of the exposure mean of altering the number of subjects, days, cycles and RVEs during data collection was simulated. Results: For all exposure parameters a unique component of variance due to normalization was present, yet small: less than 4.4% of the total variance. The resource allocation simulations indicated that marginal improvements in the precision of a group exposure mean would occur above three RVE repeats for EMG collected on one day, or beyond two RVEs for EMG collected on two or more days.

  • 5.
    Samani, Afshin
    et al.
    Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Denmark.
    Srinivasan, Divya
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Madeleine, Pascal
    Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Denmark.
    Nonlinear metrics assessing motor variability in a standardized pipetting task: Between- and within-subject variance components2015Inngår i: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 25, nr 3, s. 557-564Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 6.
    Srinivasan, Divya
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Rudolfsson, Thomas
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Department of Community Medicine and Rehabilitation, Umeå University, Umeå, Sweden.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Between- and within-subject variance of motor variability metrics in females performing repetitive upper-extremity precision work2015Inngår i: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 25, nr 1, s. 121-129Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Kinematic motor variability is extensively studied in occupational, clinical and sports biomechanics, but the consistency of most motor variability metrics have never been reported. In this study, fourteen subjects performed a repetitive pipetting task on three separate days. Movements of hand, arm and pipette tip were recorded in 3D and used to compute shoulder elevation, elbow flexion and shoulder-arm coordination angles, as well as pipette-tip endpoint precision. Cycle-to-cycle motor variability was quantified using linear dispersion measures of standard kinematics properties such as peak velocity, range of motion, and inter-segmental relative phase. Between- and within-subject consistencies of these variability metrics were quantified by variance components estimated using a nested random effects model. For most metrics, the variance between subjects was larger than that between days and cycles. Entering the variance components in statistical power equations showed that for most metrics, a total of 80-100 subjects will be required to detect a 20% difference between two groups with sufficient power, while this difference can typically be detected  in repeated-measures (paired) designs using 25 subjects. The reported between- and within-subject variance components can be used as a data base to facilitate efficient designs of future studies of kinematic motor variability.

  • 7.
    Veiersted, Kaj Bo
    et al.
    National Institute of Occupational Health, Oslo.
    Forsman, Mikael
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Hansson, Gert-Åke
    Division of Occupational and Environmental Medicine, Lund University.
    Mathiassen, Svend Erik
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Assessment of time patterns of activity and rest in full-shift recordings of trapezius muscle activity - effects of the data processing procedure2013Inngår i: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 23, nr 3, s. 540-547Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of this paper was to compare the effects of different data reduction procedures on the values of variables characterizing the time pattern of trapezius muscle activity during full work shifts. Surface electromyography (EMG) of the right and left upper trapezius muscles were obtained from 40 young subjects in different occupations, mainly electricians, hairdressers and students. The target EMG variables were gap frequency, muscle rest, and the number and duration of episodes with sustained muscle activity (from 0.13 s to 30 min as minimum duration). These variables were derived from the EMG recordings using different Root Mean Square (RMS) windows (from 0.13 to 6.38 s), and discrimination levels between "activity" and "rest" (0.5, 1 and 2 % of maximal EMG). The results give basis for practical suggestions for EMG analyses of full work shifts. For most variables, a discrimination level of 0.5% EMGmax showed to be preferable. The time proportion of muscle rest and sustained muscle activity should, in general, be preferred over the corresponding frequency measures. Sustained muscle activity should be calculated using a RMS window between 1 and 3 s, and preferably be stated in terms of variables describing time proportions of activity. Uninterrupted activity episodes longer than 10 min proved not to be a useful variable due to limited occurrence in many work shifts.

  • 8.
    Zetterberg, Camilla
    et al.
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Forsman, Mikael
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning. Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
    Richter, Hans
    Högskolan i Gävle, Akademin för hälsa och arbetsliv, Avdelningen för arbets- och folkhälsovetenskap, Arbetshälsovetenskap. Högskolan i Gävle, Centrum för belastningsskadeforskning.
    Effects of visually demanding near work on trapezius muscle activity2013Inngår i: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 23, nr 5, s. 1190-1198Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Poor visual ergonomics is associated with visual and neck/shoulder discomfort, but the relation between visual demands and neck/shoulder muscle activity is unclear. The aims of this study were to investigate whether trapezius muscle activity was affected by: (i) eye-lens accommodation; (ii) incongruence between accommodation and convergence; and (iii) presence of neck/shoulder discomfort. Sixty-six participants (33 controls and 33 with neck pain) performed visually demanding near work under four different trial-lens conditions. Results showed that eye-lens accommodation per se did not affect trapezius muscle activity significantly. However, when incongruence between accommodation and convergence was present, a significant positive relationship between eye-lens accommodation and trapezius muscle activity was found. There were no significant group-differences. It was concluded that incongruence between accommodation and convergence is an important factor in the relation between visually demanding near work and trapezius muscle activity. The relatively low demands on accommodation and convergence in the present study imply that visually demanding near work may contribute to increased muscle activity, and over time to the development of near work related neck/shoulder discomfort.

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