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The impact of visually demanding near work on neck/shoulder discomfort and trapezius muscle activity: Laboratory studies
University of Gävle, Faculty of Health and Occupational Studies, Department of Occupational and Public Health Sciences. University of Gävle, Centre for Musculoskeletal Research. Uppsala universitet, Arbets- och miljömedicin.ORCID iD: 0000-0002-2919-3921
2016 (English)Doctoral thesis, comprehensive summary (Other academic)Text
Abstract [en]

Introduction: Musculoskeletal discomfort in the neck and shoulders is common among workers performing visually demanding near work, e.g., on a computer screen, and sustained low-level muscle activity during such work can lead to work-related pain. The relationships between visual demands and muscle activity and discomfort in the neck/shoulder region are at present unclear. Aim: The aims of this thesis were to determine whether neck/shoulder discomfort and trapezius muscle activity increases during visually demanding experimental near work, and to investigate whether eye-lens accommodation is a mediating mechanism behind increased trapezius muscle activity. Methods: The four papers included are based on two experiments with different visually demanding near work tasks (duration 5 and 7 min). Trial lenses of different diopters were used to manipulate the visual demands (i.e., induce more or less accommodation) and thereby create different viewing conditions. Monocular viewing, which does not require active convergence, was used to examine the isolated effect of accommodation. Eye-lens accommodation and trapezius muscle activity were measured continuously during the visual tasks, and in one experiment the participants rated their eye and neck/shoulder discomfort at baseline and after each visual task. Results: Neck/shoulder discomfort and trapezius muscle activity increased during the visually demanding near work and participants experiencing a greater increase in eye discomfort (compared with baseline) also developed more neck/shoulder discomfort with time. There were no significant differences in muscle activity among the viewing conditions, and no effect of isolated accommodation response within the monocular viewing conditions. Conclusion: These findings indicate that accommodation per se is unlikely to mediate trapezius muscle activity. Instead, the increase in trapezius muscle activity observed here may be due to a combination of high visual attention and enhanced requirement for eye-neck (head) stabilisation. Since these results suggest that neck/shoulder discomfort may aggravate with time when the visual demands are high, it is important to provide good visual conditions in connection with visually demanding occupations.

Abstract [sv]

Introduktion: Muskelrelaterade besvär i nack- och skulderområdet är vanligt förekommande, framförallt hos individer som utför synkrävande datorarbete. En orsak till sådana besvär anses vara långvarig lågintensiv aktivitet i dessa muskler. Det är i dagsläget oklart om de belastningar som synsystemet utsätts för vid synkrävande arbete bidrar till ökad muskelaktivitet i nack/skulderregionen. Syfte: Syftet var att undersöka om experimentellt synkrävande närarbete påverkar muskelaktivitet och besvär i nack/skulderregionen, och att undersöka om aktivitet i trapezius muskeln (kappmuskeln) påverkas av ögats ackommodation, d.v.s. när linsens brytkraft förändras för att se skarpt på nära håll. Metod: De fyra delstudierna baseras på två laborativa experiment där försökspersoner (66 respektive 26 stycken) genomförde olika synkrävande uppgifter (fem och sju minuter långa). För att göra synuppgifterna mer eller mindre ansträngande för synsystemet användes linser med olika grad av brytkraft (dioptrier). Dessutom, eftersom monokulärt seende inte kräver aktiv konvergens, genomfördes tre av de fyra synuppgifterna i ena experimentet med ett öga för att undersöka den enskilda effekten av ackommodation. En autorefraktor mätte ögats ackommodation under synuppgifterna och aktiviteten i trapeziusmuskeln registreades kontinuerligt med elektromyografi (EMG). I samband med det ena experimentet skattade deltagarna sina upplevda ögon- och nack/skulderbesvär, både före experimentet (baslinje) och efter varje synuppgift. Resultat: Det synkrävande arbetet ökade både de självskattade nack/skulderbesvären och muskelaktiviteten i trapezius. De personer som upplevde en högre ökning av ögonbesvär (i förhållande till baslinjen), rapporterade också mer nack/skulderbesvär över tid. Det var varken någon signifikant skillnad i grad av muskelaktivitet mellan synuppgifterna, eller något signifikant samband mellan monokulär ackommodation och muskelaktivitet. Slutsats: Resultaten indikerar att ögats ackommodation, i sig, inte påverkar muskelaktiviteten i trapezius. Ökad muskelaktivitet i nack/skulderregionen i anslutning till synkrävande arbete kan istället bero på en kombination av höga krav på visuell uppmärksamhet och ett ökat behov av att stabilisera ögonen (huvudet) i förhållande till objektet i fokus (t.ex. texten på en bildskärm). Eftersom resultaten tyder på att synkrävande närarbete leder till ökade besvär i nack/skuldraregionen över tid, är det viktigt att utforma arbetsplatser och synkrävande arbetsuppgifter (t.ex. vid datorn) på ett sätt som främjar visuell hälsa.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2016. , 55 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1228
Keyword [en]
Accommodation, Asthenopia, Computer work, Eye-neck (head) stabilization, Muscle activity, Neck pain, Visual Attention, Visual demand, Visual ergonomics
National Category
Environmental Health and Occupational Health
Research subject
Medical Science
Identifiers
URN: urn:nbn:se:hig:diva-21511ISBN: 978-91-554-9583-1OAI: oai:DiVA.org:hig-21511DiVA: diva2:929849
Public defence
2016-06-09, Krusenstjernasalen, Kungsbäcksvägen 47, Gävle, 13:00 (English)
Opponent
Supervisors
Available from: 2016-05-20 Created: 2016-05-20 Last updated: 2016-05-20
List of papers
1. Trapezius muscle activity increases during near work activity regardless of accommodation/vergence demand level
Open this publication in new window or tab >>Trapezius muscle activity increases during near work activity regardless of accommodation/vergence demand level
2015 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 115, no 7, 1501-1512 p.Article in journal (Refereed) Published
Abstract [en]

Aim

To investigate if trapezius muscle activity increases over time during visually demanding near work.

Methods

The vision task consisted of sustained focusing on a contrast-varying black and white Gabor grating. Sixty-six participants with a median age of 38 (range 19–47) fixated the grating from a distance of 65 cm (1.5 D) during four counterbalanced 7-min periods: binocularly through −3.5 D lenses, and monocularly through −3.5 D, 0 D and +3.5 D. Accommodation, heart rate variability and trapezius muscle activity were recorded in parallel.

Results

General estimating equation analyses showed that trapezius muscle activity increased significantly over time in all four lens conditions. A concurrent effect of accommodation response on trapezius muscle activity was observed with the minus lenses irrespective of whether incongruence between accommodation and convergence was present or not.

Conclusions

Trapezius muscle activity increased significantly over time during the near work task. The increase in muscle activity over time may be caused by an increased need of mental effort and visual attention to maintain performance during the visual tasks to counteract mental fatigue.

Keyword
Attention fatigue, Accommodation, Békésy test, Compensatory effort, Contrast threshold tracking, Electromyography, Visual ergonomics
National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:hig:diva-18656 (URN)10.1007/s00421-015-3125-9 (DOI)000355872200011 ()25697148 (PubMedID)2-s2.0-84930575168 (ScopusID)
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2005-0488; 2009-1761
Available from: 2015-01-01 Created: 2015-01-01 Last updated: 2016-05-20Bibliographically approved
2. Effects of visually demanding near work on trapezius muscle activity
Open this publication in new window or tab >>Effects of visually demanding near work on trapezius muscle activity
2013 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 23, no 5, 1190-1198 p.Article in journal (Refereed) Published
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.

Keyword
Accommodation, Computer work, Electromyography, Gaze stabilization, Visual ergonomics
National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:hig:diva-15261 (URN)10.1016/j.jelekin.2013.06.003 (DOI)000324024800027 ()2-s2.0-84882875082 (ScopusID)
Available from: 2013-09-16 Created: 2013-09-16 Last updated: 2016-05-20Bibliographically approved
3. Neck/shoulder discomfort due to visually demanding near work is influenced by previous neck pain, task duration, astigmatism, eye discomfort and accommodation
Open this publication in new window or tab >>Neck/shoulder discomfort due to visually demanding near work is influenced by previous neck pain, task duration, astigmatism, eye discomfort and accommodation
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Visually demanding near work can cause eye discomfort, and eye and neck/shoulder discomfort during, e.g., computer work are associated. Here, to investigate direct effects of experimental near work on eye and neck/shoulder discomfort, 33 individuals with chronic neck pain and 33 healthy control subjects performed four visual tasks, rating eye and neck/shoulder discomfort at baseline and after each task. The cumulative performance time (reflected in the temporal order of the tasks), astigmatism, concurrent eye discomfort, and extent of accommodation all aggravated neck/shoulder discomfort. There was an interaction effect between the temporal order and eye discomfort: participants with a greater mean increase in eye discomfort also developed more neck/shoulder discomfort with time. Since moderate musculoskeletal symptoms are a risk factor for more severe symptoms, it is important to ensure a good visual environment in occupations involving visually demanding near work.

Keyword
astigmatism, computer vision syndrome, musculoskeletal disorder, oculomotor load, visual ergonomics
National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:hig:diva-21513 (URN)
Available from: 2016-04-19 Created: 2016-05-20 Last updated: 2016-05-20Bibliographically approved
4. Temporal co-variation between eye lens accommodation and trapezius muscle activity during a dynamic near-far visual task
Open this publication in new window or tab >>Temporal co-variation between eye lens accommodation and trapezius muscle activity during a dynamic near-far visual task
2015 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 5, e0126578Article in journal (Refereed) Published
Abstract [en]

Near work is associated with increased activity in the neck and shoulder muscles, but the underlying mechanism is still unknown. This study was designed to determine whether a dynamic change in focus, alternating between a nearby and a more distant visual target, produces a direct parallel change in trapezius muscle activity. Fourteen healthy controls and 12 patients with a history of visual and neck/shoulder symptoms performed a Near-Far visual task under three different viewing conditions; one neutral condition with no trial lenses, one condition with negative trial lenses to create increased accommodation, and one condition with positive trial lenses to create decreased accommodation. Eye lens accommodation and trapezius muscle activity were continuously recorded. The trapezius muscle activity was significantly higher during Near than during Far focusing periods for both groups within the neutral viewing condition, and there was a significant co-variation in time between accommodation and trapezius muscle activity within the neutral and positive viewing conditions for the control group. In conclusion, these results reveal a connection between Near focusing and increased muscle activity during dynamic changes in focus between a nearby and a far target. A direct link, from the accommodation/vergence system to the trapezius muscles cannot be ruled out, but the connection may also be explained by an increased need for eye-neck (head) stabilization when focusing on a nearby target as compared to a more distant target.

Keyword
Accommodation, Ciliary muscle, Computer work, Electromyography, Eye-neck (head) stabilization, Gaze stabilization, Visual ergonomics
National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:hig:diva-16689 (URN)10.1371/journal.pone.0126578 (DOI)000354542500115 ()25961299 (PubMedID)2-s2.0-84930675377 (ScopusID)
Funder
Forte, Swedish Research Council for Health, Working Life and Welfare, 2005-0488; 2009-1761
Available from: 2014-05-23 Created: 2014-05-23 Last updated: 2016-05-20Bibliographically approved

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