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Katherine R. Lehman

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Publications by Katherine R. Lehman (bibliography)

1994

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Lehman, Katherine R. and Marras, William S. (1994): The Effects of Human Interface Design on Wrist Biomechanics during Scanning. In: Proceedings of the Human Factors and Ergonomics Society 38th Annual Meeting 1994. pp. 616-620.

“Two window, or "bi-optic" scanners have ergonomic potential to minimize cumulative trauma disorders (CTDs) among grocery checkers. However, not all checkers utilize both windows when scanning. Four, two window scanners were tested to see whether the number of windows used had an effect on wrist acceleration, one of the most predictive indicators of CTD risk. Out of 32 subjects, 14 used only one window while scanning. These subjects were seen to have significantly higher cumulative peak wrist accelerations than those subjects that used both windows. In addition, the productivity of the one window users was significantly lower than two window users. The results indicate that two window scanners can not only increase productivity, but can reduce the risk of CTDs. However, this will only occur if checkers appreciate and choose to use both windows in their scanning activity. The large number of subjects (14 out of 32) that only used one window when scanning indicates a serious human interface problem with these types of scanners. This paper identifies the need for better scanner designs that will indicate to the user the three-dimensional scan zone created by the two windows. The design should influence one to use both windows while scanning so that wrist motions will be reduced. Most importantly, this paper identifies the importance of the relationship between cognitive and biomechanical issues when approaching a human interface problem in a product's design.”

1993

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Lehman, Katherine R., Allread, W. Gary, Wright, P. Lawrence and Marras, William S. (1993): Quantification of Hand Grip Force under Dynamic Conditions. In: Proceedings of the Human Factors and Ergonomics Society 37th Annual Meeting 1993. pp. 715-719.

“A laboratory experiment was conducted to determine whether grip force capabilities are lower when the wrist is moved than in a static position. The purpose was to determine the wrist velocity levels and wrist postures that had the most significant effect on grip force. Maximum grip forces of five male and five female subjects were determined under both static and dynamic conditions. The dominant wrist of each subject was secured to a CYBEX II dynamometer and grip force was collected during isokinetic wrist deviations for four directions of motion (flexion to extension, extension to flexion, radial to lunar, and ulnar to radial). Six different velocity levels were analyzed and grip forces were recorded at specific wrist positions throughout each range of movement. For flexion-extension motions, wrist positions from 45 degrees flexion to 45 degrees extension were analyzed whereas positions from 20 degrees radial deviation to 20 degrees ulnar deviation were studied for radial-ulnar activity. Isometric exertions were also performed at each desired wrist position. Results showed that, for all directions of motion, grip forces for all isokinetic conditions were significantly lower than for the isometric exertions. Lower grip forces were exhibited at extreme wrist flexion and extreme radial and ulnar positions for both static and dynamic conditions. The direction of motion was also found to affect grip strength; extension to flexion exertions produced larger grip forces than flexion to extension exertions and radial to ulnar motion showed larger grip forces than ulnar to radial deviation. Although, males produced larger grip forces than females in all exertions, significant interactions between gender and velocity were noted.”

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