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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.apergo.2005.12.008 Byline: James F. Knight, Chris Baber Keywords: Arm-mounted computer; Ergonomics; Fatigue; Musculoskeletal disorders; EMG; Posture; Perceived exertion; Pain; Discomfort Abstract: Wearable computers enable workers to interact with computer equipment in situations where previously they were unable. Attaching a computer to the body though has an unknown physical effect. This paper reports a methodology for addressing this, by assessing postural effects and the effect of added weight. Using the example of arm-mounted computers (AMCs), the paper shows that adopting a posture to interact with an AMC generates fatiguing levels of stress and a load of 0.54kg results in increased level of stress and increased rate of fatigue. The paper shows that, due to poor postures adopted when wearing and interacting with computers and the weight of the device attached to the body, one possible outcome for prolonged exposure is the development of musculoskeletal disorders. Author Affiliation: School of Electronic, Electrical and Computer Engineering, The University of Birmingham, Birmingham B15 2TT, UK Article History: Received 4 October 2004; Accepted 5 December 2005

INTRODUCTION The term wearable has been defined by Gemperle, Kasabach, Stivoric, Bauer, and Martin (1998) as implying the use of the human body as a support for some product. Extending […], Wearable computer comfort can be affected by numerous factors, making its assessment based on one value with one scale inappropriate. This paper presents a tool that measures wearable comfort across six dimensions: emotion, attachment, harm, perceived change, movement, and anxiety. The dimensions for these comfort rating scales were specifically developed for wearable equipment assessment by applying multidimensional scaling to a comfort term association matrix developed using the results of groupings of wearable computer comfort terms. Testing the scales oil four different types of wearable computer showed that the scales can be used to highlight differences in comfort between different types of technology for different aspects of comfort. An intraclass correlation of .872 suggested that the scales were used with a high level of reliability. A second study showed that modifications made to a wearable computer resulted in improvements in comfort, although they were not significant (p > .05). A potential application for this research is as an aid to designers and researchers for assessing the wearability, in terms of comfort, of wearable computer devices and to determine the effectiveness of any modifications made to the design of a wearable device.

Background: The increasing use of helmet-mounted displays in aviation raises issues of head-supported weight and neck musculoskeletal function, especially during acceleration., Objectives: This study aimed to quantify musculoskeletal stress as weight was added to the front of the head in different head positions and determine the effectiveness of a counterbalance in reducing stress., Methods: There were 20 subjects who participated. The study required that the subject move his head every 10 s for 10 min to one of five positions that were assumed to represent those readily adopted in everyday situations: neutral, 30 degrees extended, 30 degrees flexed, 35 degrees left rotated, and 35 degrees right rotated. Of the subjects, 10 repeated the test while wearing a GSMK6 helmet, and when 0.5 kg, 1.0 kg, or 2.0 kg was added to the front of the helmet. The other 10 subjects repeated the test but with counterbalances. During testing, EMG was recorded from the neck extensors and sternocleidomastoid muscle. Pain levels were recorded using the Borg-CR10 scale., Results: Changes in head position from neutral resulted in significant increases of EMG amplitude (mean +/- SD) in the neck extensors of up to 18 +/- 13% (p < 0.05), and due to head load by 46 +/- 33% (p < 0.05) with a frontal load of 2 kg. Sternocleidomastoid EMG showed little change due to increases in load but increased significantly by up to 265 +/- 227% of the neutral position (p < 0.05) when the head was rotated., Conclusions: The use of head-mounted displays presents the risk of detrimental effects to the musculoskeletal system. Determining the effect of added weight requires a knowledge of working head postures.