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IMPACT OF DESK ORIENTATION ON MUSCLE ACTIVATION IN LEFT-HANDED SUBJECTS WHILE WRITING

Abstract

C. Cozza, M. Bergerud, P. Henricksen, A. Harkins, B. Higginson

Gonzaga University, Spokane, WA

PURPOSE: Changing the design of common tools such as a desk to better fit the needs of the user can lead to increased comfort and even decreased risk of overuse injuries. Only 10-13% of the population of the United States is left-handed, and therefore the majority of office and school supplies, including desks, are designed for right-handed individuals. Studies have shown that left-handers experience greater wrist flexion, forearm muscle activation, and total upper extremity muscle activation. Thus, a desk designed for left-handed individuals could result in greater efficiency and less discomfort in note-taking, and a decreased risk for overuse injuries. It was hypothesized that left-handed individuals would experience less upper arm, forearm, and neck muscle activation when writing at a left-handed desk rather than a right-handed desk. METHODS: Left-handed subjects (n=14) aged 18-22 completed four trials of writing a passage at two desks. One desk was a standard auditorium sized right-handed desk, and the other was a modified left-handed desk. EMG electrodes were placed on the Flexor Carpi Ulnaris (FCU), Extensor Carpi Radialis (ECR), Biceps Brachii (BB), Anterior Deltoid (AD), and Upper Trapezius (UT) of their left arm. Mean muscle activation was collected continuously throughout each writing trial. Subjects were instructed to sit in a natural writing position and copy down two different paragraphs from the screen in front of them. Each subject performed two trials at each desk. RESULTS: Muscle activation of the BB and AD were significantly greater, by 23.14 ± 29.67 percent (p=0.012) and 76.36 ± 45.49 (p<0.001) percent respectively, while writing at the right-handed desk compared to the left-handed desk. No differences in muscle activation were observed in the other muscles (FCU p=0.799, ECR p=0.180, UT p=0.061). CONCLUSION: Muscle activation was greater in two muscles (BB and AD) at the right-hand desk compared to the left-hand desk, indicating that left-handed individuals have greater muscle activation at a typical auditorium desk.

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