Functional workspace for precision manipulation between thumb and fingers in normal hands Li-Chieh Kuo a, * , Haw-Yen Chiu b , Cheung-Wen Chang c , Hsiu-Yun Hsu d , Yun-Nien Sun c a Department of Occupational Therapy, National Cheng Kung University, 1 University Road, Tainan 701, Taiwan, ROC b Department of Surgery, National Cheng Kung University, 1 University Road, Tainan 701, Taiwan, ROC c Department of Computer Science and Information Engineering, National Cheng Kung University, 1 University Road, Tainan 701, Taiwan, ROC d Department of Physical Medicine and Rehabilitation, National Cheng Kung University, 1 University Road, Tainan 701, Taiwan, ROC Received 14 January 2008; received in revised form 25 July 2008; accepted 28 July 2008 Abstract Prehensile functions of hand are based on thumb–finger relationships which are regarded as an essential element in various manip- ulations of our daily living activities. Although the maximal workspace provides clinicians a way to comprehend the ranges of digital movements, little is known about the ‘‘functional workspace” based on thumb–finger relationships. This study defines the functional workspace of the precision thumb–finger grasp as the range of all possible positions in which thumb-tip and each fingertip can simul- taneously contact each other. We present a quantitative method for measuring the functional workspace of the human hand. The maximal motion trajectories of thumb-tip and fingertips of twenty subjects were recorded using a video-capture system. The func- tional workspace of the precision manipulation was calculated via numerical methods based on the maximal workspaces obtained of the thumb-tip and fingertip motions. The ratios of the functional workspace with respect to the maximal workspace of the index, middle, ring and little fingers were calculated as 33.7%, 27.1%, 23.5% and 19.1%, respectively. Although the present approach is still a descriptive work which might require more validations or evidences to justify, the results obtained may become normal standards for practical use in objective handicapped authentications, insurance claims, and rehabilitation programs as well as criteria for ergonomic design con- siderations in the near future. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Functional workspace; Motion analysis; Hand kinematics; Precision manipulation 1. Introduction The ultimate goal for every patient, hand surgeon and therapist is achieving better functional recovery after hand injuries. Observation of prehensile performances is one of the most common strategies in clinical practice for inspect- ing the condition of functional restoration. Suitable flexi- bility, sufficient strength, and intact sensation are required based on a well-coordinated thumb–finger rela- tionship to achieve a prehensile manipulation (Marzke, 1997; Moran and Berger, 2003). This relationship is usually regarded as an essential element in a variety of human tasks that require power grip, prehensile grasp, pad-to- pad, tip-to-tip and key pinch or similar manipulations in daily living activities. Previous studies reported that many fine manual tasks require precise dexterity with suitable positioning or movement as well as appropriately scaled grip force of the thumb and fingers (Dun et al., 2007; Johansson and Cole, 1992; Johansson and Westling, 1984; Li and Nimbarte, 2006). The manual dexterity of the human hand is, however, easily disturbed by musculo- skeletal disorders and peripheral nerve injuries of the hand (Muggleton et al., 1999). Although many reports and appa- ratuses have been presented to assess impaired grip/muscu- 1050-6411/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jelekin.2008.07.008 * Corresponding author. Tel.: +886 6 2353535x5908; fax: +886 6 2376604. E-mail address: jkkuo@mail.ncku.edu.tw (L.-C. Kuo). Available online at www.sciencedirect.com Journal of Electromyography and Kinesiology 19 (2009) 829–839 www.elsevier.com/locate/jelekin