The Effect of Wrist Rests and Forearm Support during Keyboard and Mouse Use

Supporting the forearm on the work surface during keyboard operation may increase comfort, decrease muscular load of the neck and shoulders, and decrease the time spent in ulnar deviation. Wrist rests are used widely in the workplace and are more commonly being incorporated in keyboard design. The aim of this study was to examine the effect of wrist rest use on wrist posture during forearm Support. A laboratory based, experimental study was conducted (subjects n = 15) to examine muscle activity and wrist Postures during keyboard and mouse tasks in each of' two conditions; wrist rest and no wrist rest. There were no significant differences for right wrist flexion/extension between use of a wrist rest and no wrist rest for keyboard or mouse use. Left wrist extension was significantly higher without a wrist rest than with a wrist rest during keyboard use (df = 14; t = 2.95; p = 0.01; d = 0.38). No differences with respect to use of a wrist rest were found for the left or right hand for ulnar deviation For keyboard or mouse use. There were no differences in muscle activity between the test conditions for keyboard use. Relevance to industry Wrist rests are used widely in the workplace and are more commonly being incorporated in keyboard design. Use of a wrist rest in conjunction with forearm support when using a conventional desk does not appear to have any impact on wrist posture or muscle activity during keyboard use. (C) 2004 Elsevier B.V. All rights reserved.

The effect of upper extremity support on upper extremity posture and muscle activity during keyboard use

Forearm support during keyboard use has been reported to reduce neck and shoulder muscle activity and discomfort. However, the effect of forearm support on wrist posture has not been examined. The aim of this study was to examine the effect of 3 different postures during keyboard use: forearm support, wrist support and floating. The floating posture (no support) was used as the reference condition. A wrist rest was present in all test conditions. Thirteen participants completed 20 min wordprocessing tasks in each of the test conditions. Electromyography was used to monitor neck, shoulder and forearm muscle activity. Bilateral and overhead video cameras recorded left and right wrist extension, shoulder and elbow flexion and radial and ulnar deviation. The forearm support condition resulted in significantly less ulnar deviation (

Bimanual coordination: constraints imposed by the relative timing of homologous muscle activation

It has often been supposed that patterns of rhythmic bimanual coordination in which homologous muscles are engaged simultaneously, are performed in a more stable manner than those in which the same muscles are activated in an alternating fashion. In order to assess the efficacy of this constraint, the present study investigated the effect of forearm posture (prone or supine) on bimanual abduction-adduction movements of the wrist in isodirectional and non-isodirectional modes of coordination. Irrespective of forearm posture, non-isodirectional coordination was observed to be more stable than isodirectional coordination. In the latter condition, there was a more severe deterioration of coordination accuracy/stability as a function of cycling frequency than in the former condition. With elevations in cycling frequency, the performers recruited extra mechanical degrees of freedom, principally via flexion-extension of the wrist, which gave rise to increasing motion in the vertical plane. The increases in movement amplitude in the vertical plane were accompanied by decreasing amplitude in the horizontal plane. In agreement with previous studies, the present findings confirm that the relative timing of homologous muscle activation acts as a principal constraint upon the stability of interlimb coordination. Furthermore, it is argued that the use of manipulations of limb posture to investigate the role of other classes of constraint (e.g. perceptual) should be approached with caution because such manipulations affect the mapping between muscle activation patterns, movement dynamics and kinematics.

Effector dynamics of rhythmic wrist activity and its implications for (modeling) bimanual coordination

To examine the role of the effector dynamics of the wrist in the production of rhythmic motor activity, we estimated the phase shifts between the EMG and the task-related output for a rhythmic isometric torque production task and an oscillatory movement, and found a substantial difference (45-52degrees) between the two. For both tasks, the relation between EMG and task-related output (torque or displacement) was adequately reproduced with a physiologically motivated musculoskeletal model. The model simulations demonstrated the importance of the contribution of passive structures to the overall dynamics and provided an account for the observed phase shifts in the dynamic task. Additional simulations of the musculoskeletal model with added load suggested that particular changes in the phase relation between EMG and movement may follow largely from the intrinsic muscle dynamics, rather than being the result of adaptations in the neural control of joint stiffness. The implications of these results are discussed in relation to (models of) interlimb coordination in rhythmic tasks. (C) 2004 Elsevier B.V. All rights reserved.

The effect of forearm support on musculoskeletal discomfort during call centre work

Using a computer keyboard with the forearms unsupported has been proposed as a causal factor for neck/shoulder and arm/hand diagnoses. Recent laboratory and field studies have demonstrated that forearm support might be preferable to working in the traditional floating posture. The aim of this study was to determine whether providing forearm Support when using a normal computer workstation would decrease musculoskeletal discomfort in intensive computer users in a call centre. A randomised controlled study (n = 59), of 6 weeks duration was conducted. Thirty participants (Group 1) were allocated to forearm support using the desk surface with the remainder (Group 2) acting as a control group. At 6 weeks, the control group was also set up with forearm support. Both groups were then monitored for another 6 weeks. Questionnaires were used at 1, 6 and 12 weeks to obtain information about discomfort, workstation setup, working posture and comfort. Nine participants (Group 1 n = 6, Group 2 n = 3) withdrew within a week of commencing forearm support either due to discomfort or difficulty in maintaining the posture. At 6 weeks, the group using forearm support generated significantly fewer reports of discomfort in the neck and back, although the difference between the groups was not statistically significant. At 12 weeks, there were fewer reports of neck, back and wrist discomfort when preintervention discomfort was compared with post intervention discomfort. These findings indicate that for the majority of users, forearm support may be preferable to the floating Posture implicit in current guidelines for computer workstation setup. (C) 2004 Elsevier Ltd. All rights reserved.

Sitting posture affects pelvic floor muscle activity in parous women: An observational study

Question Do different sitting postures require different levels of pelvic floor and abdominal muscle activity in healthy women? Design Observational study. Participants Eight parous women with no pelvic floor dysfunction. Outcome measures Bilateral activity of pelvic floor muscles (assessed vaginally) and two abdominal muscles, obliquus internus abdominis and obliquus externus abdominis, during three sitting postures. Results There was a significant increase in pelvic floor muscle activity from slump supported sitting (mean 7.2% maximal voluntary contraction, SD 4.8) to both upright unsupported sifting (mean 12.6% maximal voluntary contraction, SD 7.8) (p = 0.01) and very tall unsupported sitting (mean 24.3% maximal voluntary contraction, SD 14.2) (p = 0.004). Activity in both abdominal muscles also increased but did not reach statistical significance. Conclusion Both unsupported sitting postures require greater pelvic floor muscle activity than the supported sitting posture.

The impact of computer display height and desk design on 3D posture during information technology work by young adults

Computer display height and desk design to allow forearm support are two critical design features of workstations for information technology tasks. However there is currently no 3D description of head and neck posture with different computer display heights and no direct comparison to paper based information technology tasks. There is also inconsistent evidence on the effect of forearm support on posture and no evidence on whether these features interact. This study compared the 3D head, neck and upper limb postures of 18 male and 18 female young adults whilst working with different display and desk design conditions. There was no substantial interaction between display height and desk design. Lower display heights increased head and neck flexion with more spinal asymmetry when working with paper. The curved desk, designed to provide forearm support, increased scapula elevation/protraction and shoulder flexion/abduction.