Owing to the space limit the standing visual display terminal (VDT) workstation was necessary and can not be replaced by sitting VDT workstation in practice at some workplaces such as at the semiconductor fabrication cleaning room. The guides or recommendations for standing VDT workstation were few. Only recommendation based on standing elbow height was reported. The elbow-height based recommendation for stand VDT workstation equipped with laptop PC will still possibly result in the neck/shoulder discomfort because of the lower monitor height. We wonder that will the subjects prefer to elevate the keyboard height higher than the standing elbow height to ease the shoulder and neck discomfort. Through, in opposite, this will increase the upper arm discomfort.
There are two stages of experiments. Aims of the first experiment are to evaluate the preferred settings for standing VDT workstation especially for laptop PC and the associated postural and workstation settings and muscular loads. Results of the first stage of experiments show that the subjects still preferred to set keyboard height at about standing elbow height. Therefore, the second stage of experiment aimed to evaluate the effects of increasing laptop stand tilt on the posture and muscular load of the upper extremity.
There were forty and twenty-four healthy female university students participated in the two stages of experiments respectively. They were all familiar with laptop and desktop PC use. The explored independent variables included type of computer (12.1- and 14-inch laptops and desktop PC with 15-inch monitor), initial desk height setting (i.e. from highest/lowest position before adjustment), and initial laptop stand tilt setting (i.e. from 30 degrees to preference, flat, from 0 degrees to preference). All independent variables are within-subject variables. Electromyograph and dynamic single/two-axis goniometers were utilized to evaluate the associated muscular loads and postural settings for the upper extremity. Each subjects completed all sessions of experiments which were completely randomized to reduce fatigue and learning effects. The first and second stage of experiment took about 180 and 165 minutes respectively for each subject. Besides, a questionnaire was used to evaluate the subjective discomfort after each session of experiment.
Results of the repeated measures ANOVAs showed that initial settings significantly affected the preferred desk height settings. However, no significant differences for the preferred desk height among the three experiment computers were found. The preferred desk height in average was quite close to the average standing elbow height of the subjects which indicated that subjects did not elevate the keyboard higher than their elbow height to ease the large neck flexion and gaze angle for the two laptops. Besides, significantly large neck flexion angle, gaze angle, and muscular loads were reported for the 12 inch laptop compared with the other two types of computers. The desktop PC with 15 inch monitor was found with the smallest neck flexion and gaze angles and the muscular loads. Results of the second stage of experiments showed that the preferred laptop stand tilt was significantly affected by the initial laptop stand tilt settings in the second experiment. 54.2% of subjects preferred the increased laptop stand tilt than the flat setting. The preferred range of laptop stand tilt was between 4.8 to 6.8 degrees. The results also showed that the preferred desk height of VDT workstation was not affected by types of monitor and initial laptop stand tilt settings. The increased laptop stand tilt resulted in elevated monitor center height and therefore decreased gaze angle to monitor center and downwards gaze angle. However, minor but significant increased wrist extension angle muscular load for left deltoids were found. No significant differences were reported for the subjective discomfort data of the two experiments.
Recommendations of our study for standing VDT workstation can be applied to the improvement of the design of standing VDT workstation of semiconductor fabrication.
