Browsing by Author "Mathiassen, Svend Erik"

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    Consistency of Sedentary Behavior Patterns among Office Workers with Long-Term Access to Sit-Stand Workstations
    Huysmans, Maaike A.; Srinivasan, Divya; Mathiassen, Svend Erik (Oxford University Press, 2019-04-22)
    Introduction: Sit-stand workstations are a popular intervention to reduce sedentary behavior (SB) in office settings. However, the extent and distribution of SB in office workers long-term accustomed to using sit-stand workstations as a natural part of their work environment are largely unknown. In the present study, we aimed to describe patterns of SB in office workers with long-term access to sit-stand workstations and to determine the extent to which these patterns vary between days and workers. Methods: SB was objectively monitored using thigh-worn accelerometers for a full week in 24 office workers who had been equipped with a sit-stand workstation for at least 10 months. A comprehensive set of variables describing SB was calculated for each workday and worker, and distributions of these variables between days and workers were examined. Results: On average, workers spent 68% work time sitting [standard deviation (SD) between workers and between days (within worker): 10.4 and 18.2%]; workers changed from sitting to standing/ walking 3.2 times per hour (SDs 0.6 and 1.2 h−1); with bouts of sitting being 14.9 min long (SDs 4.2 and 8.5 min). About one-third of the workers spent >75% of their workday sitting. Between-workers variability was significantly different from zero only for percent work time sitting, while betweendays (within-worker) variability was substantial for all SB variables. Conclusions: Office workers accustomed to using sit-stand workstations showed homogeneous patterns of SB when averaged across several days, except for percent work time seated. However, SB differed substantially between days for any individual worker. The finding that many workers were extensively sedentary suggests that just access to sit-stand workstations may not be a sufficient remedy against SB; additional personalized interventions reinforcing use may be needed. To this end, differences in SB between days should be acknowledged as a potentially valuable source of variation.
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    Consistent individual motor variability traits demonstrated by females performing a long-cycle assembly task under conditions differing in temporal organisation
    Jackson, Jennie A.; Srinivasan, Divya; Mathiassen, Svend Erik (2020-05)
    Research suggests an association between motor variability (MV) during repetitive work and work-related musculoskeletal disorders (MSDs). However, whether MV is a consistent individual trait, even across working conditions or tasks, remains unknown. This study assessed whether individual MV traits were consistent during complex work performed under different temporal conditions. Fifteen women performed cyclic assembly under four conditions differing in pace and organisation (line-type, batch-type). MV of trapezius muscle activity and upper arm elevation was quantified and partitioned into variance components. For all MV metrics, a non-zero between-subjects variance was found, indicating consistent individual MV traits across conditions. Variance between subjects was higher for electromyography (EMG) MV metrics compared with kinematic metrics. Our results showed individuals exhibited consistent MV traits across working conditions differing in pace and production process. Further research is needed to understand whether MV is an individual predictive factor for MSD onset or progression.
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    Gender differences in fatigability and muscle activity responses to a short-cycle repetitive task
    Srinivasan, Divya; Sinden, Kathryn E.; Mathiassen, Svend Erik; Cote, Julie N. (Springer, 2016-12-01)
    Purpose Epidemiological research has identified women to be more susceptible to developing neck-shoulder musculoskeletal disorders when performing low-force, repetitive work tasks. Whether this is attributable to gender differences in fatigability and motor control is currently unclear. This study investigated the extent to which women differ from men in fatigability and motor control while performing a short-cycle repetitive task. 113 healthy young adults (58 women, 55 men) performed a standardized repetitive pointing task. The task was terminated when the subject's perceived exertion reached 8 on the Borg scale. The time to task termination, and changes in means and cycle-to-cycle variabilities of surface electromyography signals from start to end of the task, were compared between women and men, for the upper trapezius, anterior deltoid, biceps and triceps muscles. Women and men terminated the task after 6.5 (SD 3.75) and 7 (SD 4) min on average (p > 0.05). All four muscles showed an increase of 25-35 % in average muscle activity with fatigue (no significant sex differences). However, men exhibited a higher increase than women in trapezius muscle variability with fatigue (31 vs. 7 %; p < 0.05), and a decrease in biceps muscle variability where women had an increase (-23 vs. 12 %; p < 0.05). Our results suggest that women and men may not differ in the ability to perform repetitive tasks at low-to-moderate force levels. However, differences in motor control strategies employed in task performance may explain gender differences in susceptibility to developing musculoskeletal disorders when performing repetitive work for prolonged periods in occupational life.
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    Muscle Activation Patterns and Chronic Neck-Shoulder Pain in Computer Work
    Kelson, Denean M. (Virginia Tech, 2018-04-20)
    Prolonged computer work is associated with high rates of neck and shoulder pain symptoms, and as computers have become increasingly more common, it is becoming critical that we develop sustainable interventions targeting this issue. Static muscle contractions for prolonged periods often occur in the neck/shoulder during computer work and may underlie muscle pain development in spite of rather low relative muscle load levels. Causal mechanisms may include a stereotypical recruitment of low threshold motor units (activating type I muscle fibers), characterized by a lack of temporal as well as spatial variation in motor unit recruitment. Based on this theory, although studies have postulated that individuals with chronic neck-shoulder pain will show less variation in muscle activity compared to healthy individuals when engaged in repetitive/monotonous work, this has seldom been verified in empirical studies of actual computer work. Studies have rarely addressed temporal patterns in muscle activation, even though there is a consensus that temporal activation patterns are important for understanding fatigue and maybe even risks of subsequent musculoskeletal disorders. This study applied exposure variation analysis (EVA) to study differences in temporal patterns of trapezius muscle activity as individuals with and without pain performed computer work. The aims of this study were to: Assess the reliability of EVA to measure variation in trapezius muscle activity in healthy individuals during the performance of computer work; Determine the extent to which healthy subjects differ from those with chronic pain in trapezius muscle activity patterns during computer work, measured using EVA. Thirteen touch-typing, right-handed participants were recruited in this study (8 healthy; 5 chronic pain). The participants were asked to complete three 10-minute computer tasks (TYPE, CLICK and FORM) in two pacing conditions (self-paced, control-paced), with the healthy group completing two sessions and the pain group completing one. Activation of the upper trapezius muscle was measured using surface electromyography (EMG). EMG data were organized into 5x5 EVA matrices with five amplitude classes (0-6.67, 6.67-20, 20-46.67, 46.67-100, >100% Reference Voluntary Exertion) and five duration classes (0- 1, 1-3, 3-7, 7-15, >15 seconds). EVA marginal distributions (along both amplitude and duration classes) for each EVA class, as well as summary measures (mean and SD) of the marginal sums along each axis were computed. Finally, “resultant” mean and SD across all EVA cells were computed. The reliability in EVA indices was estimated using intra-class correlation coefficients (ICC), coefficient of variation (CV) and standard error of measurement (SEM), computed from repeated measurements of healthy individuals (aim 1), and EVA indices were compared between groups (aim 2). Reliability of EVA amplitude marginal sums ranged from moderate to high in the self-paced condition and low to moderate in the control-paced condition. The duration marginal sums were moderate in the self-paced condition and moderate to high in the control-paced condition. The summary measures (means and SDs) were moderate to high in both the self-paced and control-paced condition. Group comparisons revealed that individuals with chronic pain spent longer durations of work time in higher EVA duration categories, exhibited larger means along the amplitude, duration and in the resultant, and higher EVA SD in the amplitude and duration axes as compared to the healthy group. To our knowledge, this is the first study to report on the reliability of EVA applied specifically to computer work. Furthermore, EVA was used to assess differences in muscle activation patterns as individuals with and without chronic pain engaged in computer work. Individuals in the pain group seemed to exhibit prolonged sustained activation of the trapezius muscle to a significantly greater extent than controls, even though they did not experience pain during the performance of the computer tasks (as obtained through self-reports). Thus, these altered muscle recruitment patterns observed in the pain subjects, even in the absence of task-based pain/discomfort, are suggestive of chronic motor control changes occurring in adaptation to pain, and may have implications for the etiology of neck and upper-limb musculoskeletal disorders.