The main purpose of the studies presented in this thesis wasto measure and quantify shoulder load in computerised officework. Shoulder load was studied during a whole working day andin different work tasks. Shoulder and arm load during keyboardwork and with different modes of physical computer interactionwas also studied. The purpose was to determine whether load, orshoulder and neck complaints change with changes in workcontent or work task distribution. This thesis is based on fivepapers, of which two are from laboratory studies and three froma field study ranging over 1.5 years.
Shoulder and forearm load in keyboard work with threetypewriters (mechanical, electromechanical and electronic) andtwo personal computer keyboards (traditional and angled) wasexamined with electromyography. The task was input of a giventext. As expected work on the mechanical typewriter increasedforearm muscular activity. Work on the electronic typewriter,which had extremely low key stroke force, increased righttrapezius musclar activity compared to the mechanicaltypewriter and to the angled keyboard. Work on this typewriteralso increased flexor forearm activity compared to work on thetraditional keyboard, as weill as forearm extensor activitycompared to the angled keyboard. No differences were foundbetween using the ordinary keyboard and the angledkeyboard.
Shoulder and arm load in work with different modes ofphysical computer interaction was also studied withelectromyography. The four modes tested in word processingwere: keyboard, keyboard supplemented with a computer mouse,keyboard with computer mouse and arm support movable in threeplanes, and keyboard with Trackpoint device placed in thecentre of the keyboard. The interaction modes were evaluatedthrough perceived strain and individual preference. Muscularload from ordinary handwriting was tested as well. Shoulderload was higher during mouse work, while Trackpoint andkeyboard-only use increased forearm load. The two latter werealso found more strenuous to the forearm. Use of the armsupport decreased shoulder muscular load, as did Trackpointuse. However, the arm support increased forearm load comparedto computer mouse use without support. Handwriting increasedforearm muscular load.
Physical and psychosocial effects of the reorganisation of adata processing unit were studied at the workplaces. Thereorganisation aimed at providing the data entry operators withother, less repetitive work tasks. Shoulder load was measuredwith electromyography. Work postures and movements wereexamined via the parameters upper-arm elevation, time seatedand distance walked. Work tasks were studied usingself-reported diaries and video recordings, whilemusculoskeletal disorders were examined clinically. This studywas conducted over 1.5 years with two main data collectingparts. The subjects had more desk work time afterthereorganisation. Desk work involved more muscular load than dataentry did. However, the reorganisation did not affect whole-dayshoulder muscular activity. Work postures changed withincreased upper-arm elevation but there were no changes in timeseated or in distance walked. An improvement inneck-and-shoulder disorders was noted. There was a greatdivergence between the subjects experienced data entry time andthe actual time read from the video recordings.
Conclusions. Different office work tasks involve differentwork load, which might allow an important variation in muscularload. Different computer interaction modes also affordalterations in muscular load. Operators should thereforeperform different and varied work tasks, using different inputdevices; and they should change between them. Touch-sensitivekeys with short key travel should be avoided.
Keywords:arm; data entry; disorder; electromyography;input device; neck; shoulder; upper-arm; work movement; workorganisation; work posture; work task; work taskdistribution
Institutionen för miljöskydd och arbetsvetenskap , 1997. , 54 p.