Wrist Posture in Office Work - Fundamentals and Assessment Tools for Occupational Ergonomics - page 763

39
Wrist Posture in
Office Work

39.1 Introduction — Ergonomic Relevance . . . ....... 39-1
39.2 Anatomic vs. Physiologic Wrist Neutral Zone .... 39-2
39.3 Wrist Neutral Zone — Experimental Evidence . . . 39-2

Self-Selected Wrist Position † EMG Muscle Activity
39.4 Keyboarding and Upper Extremity ............ 39-5
Risk Factors for CTS † The Effect of Alternative Design on
CTS Risk Factors † Training Effect on Typing on Ergonomic
Keyboards
39.5 Conclusions and Summary .................. 39-11

Mircea Fagarasanu
Shrawan Kumar
University of Alberta

39.1 Introduction — Ergonomic Relevance

In the recent past, cumulative trauma disorders (CTDs) have been the fastest growing occupational health
problem. Compared to 1981 when only 24% of all occupational musculoskeletal disorders were CTD, in
1992 almost 66% of all work related illnesses reported in the United States were attributed to this category
(Bureau of Labor Statistics, 1994). Since changes have occurred in many jobs during recent years (charac-
terized by less force demands and increased mental load, higher social stress leading to a sustained
increase in muscle load) (Viikari-Juntura and Riihimaki, 1999), this trend is expected to continue.
This trend is even more visible in office work. Hence, ergonomic intervention becomes very important.
In the last century, the keyboards have constituted a constant presence in the office setting. While at the
beginning designers addressed mostly the mechanical aspect, the next period (20-25 yr) emphasized
increasing performance. Lately typist fatigue, muscular strain, perceived pain, and ergonomics interven-
tions have been the focus. Currently, the computer keyboard is the primary input device for data entry
tasks. The office work-related musculoskeletal problems are due to the fact that although the keyboard is
often a nonadjustable device, all the computer users regardless of age, gender, performance, and anthro-
pometric characteristic use it.
Carpal tunnel syndrome (CTS) is the “chief occupational hazard of the 90s” — disabling workers in
epidemic proportions (U.S. Department of Labor, 1999). Currently, over 8 million Americans suffer from
CTS (U.S. Department of Labor, 1999). In United States alone, approximately 260,000 carpal tunnel
release operations are performed each year, with almost half of the cases considered to be work
related (NCHS, 2000). Among all work-related upper extremity disorders (WRUEDs), CTS has the
biggest impact in the office workers' health. Also, the medical and nonmedical costs for CTS are the
highest among all upper extremity musculoskeletal disorders. Since 66% of the entire population
spends 33% of their time at work (WHO, 1995 cited by Kumar et al., 1997), and the incidence of
CTS is on the rise (Hedge and Powers, 1995) an association may be argued. Almost 25% of all cases

39-1