Wrist Rest Primer
Wrist Rest Primer
Wrist Rest - An Ergonomic Primer
By David Gilkey, D.C., Ph.D, CPE
Director, Environmental & Radiological Health Sciences
Colorado State University
Wrist rests facilitate the support of the forearms when inputting data
into computers. Some computer users prefer wrist support during data
entry and other users do not. Data reveals that as much as 50% percent
of users may prefer wrist support during computer use. A well-designed
workstation may be equipped with a wrist rest if it’s the user’s
preference. It is presently estimated that 45 million American workers
spend some time each day using a computer and keyboard. Approximately
30 million workers use the computer, keyboard, and pointing devices as
their primary work equipment each day, all day, and up to 8 hours per
day or more. Computer use has been linked to several types of injuries
known as “Upper Extremity Repetitive Stress Injuries” (UE-RSI's),
“Cumulative Trauma Disorders” (CTDs), or “Work Related Musculoskeletal
Disorders” (WRMSDs). RSIs, CTDs, and WRMSDs are associated with the
upper extremities (UE) or arms, forearms, wrists, hands, and fingers.
Common UE –RSI disorders associated with computer input devices include
Carpal Tunnel Syndrome (CTS), Tendonitis, and Tenosynovitis effecting
the hands, wrists, and forearms as well as Neck Tension Syndrome. The
Bureau of Labor and Statistics (BLS) reported that the incidence of such
disorders has increased 770% in past decades (BNA, 1995). Several
studies have clearly shown a definitive link between UE-RSIs and
computer use (NIOSH, 1997). Ergonomics is the premier science, which
concerns itself with humans at work and the many aspects of the “Human
Computer Interface” (HCI). Studies clearly demonstrate a scientific
basis for ergonomic design of computer workstations. The following is
an overview of ergonomic issues related to wrist rests.
Definitions and Terms:
A) Wrist rest – This equipment is designed to assist in the support
of the weight of the forearm during computer use. A wrist rest may be
built into the keyboard, tray, computer desk, or added aftermarket to
the workstation layout.
B) UE Support - This is the shared load transferred to the wrist
rest and relieved from the muscles of the UEs. Support can vary
depending on the amount of contact pressure permitted by the user.
C) Contact Pressure – This describes the pressure in “Pounds” or
“Newtons” resulting from contact of forearms or wrists to the edge of
the work surface or wrist rest.
D) Static Loading – This is contraction of muscles to hold one’s body
position without much motion. Holding UE in the fixed position for
computing is considered static loading. This is in contrast to dynamic
loading, which is muscle contraction with good motion such as in
E) Impaired circulation – This describes the loss of normal
circulation to the hands and fingers resulting from direct contact
F) Spinal Unloading – To decrease the weight on the spine.
3) How Ergonomic Wrist Rests Address These Issues:
A) The use of a wrist rest is completely an individual preference.
Studies suggest that approximately 50% of computer users enjoy the
benefits of wrist rests. Ergonomic wrist rests are designed to
distribute weight from the UE over a broader area for those wishing to
have support of upper limbs during computing. Studies have shown that
wrist rest users benefit by direct support of the UE weight, spinal
unloading, and decreased muscle activity in shoulders. Ergonomic wrist
rests are often made of “hard foam”, “rubber” or “Jelly-like” substances
that do not have sharp edges and will conform to and broaden the
contact area. Wrist rests may be designed straight, curved, or flexible
to conform to keyboard design user’s need. Some wrist rests are built
into the keyboard, computer table, or added after the system is
purchased. The keyboard tray or typing table must have adequate room to
place the writs rest near the keyboard. The benefits of wrist rests
include prolong endurance, increased comfort, faster recovery, and
reduced risk of injury.
B) In previous studies ergonomic wrist rests have demonstrated their ability to bear between
15 N (or 3lbs.) to 35 N (or 8 lbs.) of the weight of the UE. The
reduced load to the shoulder muscles results in less fatigue and more
comfort during keying. Electromyography (EMG) of the UE and shoulders
readily demonstrates that the muscles do not work as hard when wrist
rests are used compared to when they are not. Users do not report
performance decrement. The benefits of decreased muscle activity
results in prolong endurance, increased comfort, faster recovery, and
reduced risk of injury.
C) Ergonomic wrist rest is designed to broaden and soften contact
areas minimizing focused pressure to the skin and blood vessels that
might cause injury or impaired circulation. Forces as small as one
ounce per square inch have been shown to adversely affect circulation
and predispose injury to UE. Ergonomic wrist rests are designed to
avoid contact related stress while supporting the weight of the UE.
D) Supporting any portion of the UE will decrease the static load
applied to shoulder muscles. Static loads above 15% of maximum
contraction may predispose the muscles to fatigue, breakdown, and
injury. A reduction of 3 lbs. to 8lbs. in forearm weight results in
substantial reduction of shoulder stress. Ergonomic wrist rests aid in
the support of UE and reduce injury potential.
E) Ergonomic wrist rests aid in maintaining normal circulation by
decreasing static load to muscles contracted to lift and hold limb
position during computing. Muscles that contract vigorously quickly use
their energy supply and starve for more oxygen and sugar. Using a
wrist rest reduces the amount of contraction necessary to hold the limb
in position thereby reducing the use of oxygen and energy.
F) Studies suggest that supporting the weight of the UE results in
decreased stress to the low back. The low back supports the entire
upper body weight and is also susceptible to static loading. Shared
loading by wrist rests adds to relief from static loading in the spine.
A) Wrist rests are a personal preference. The data suggest there are
several benefits including increased comfort, decreased muscle
contraction, and static loading of the shoulders and spine. Ergonomic
designs optimize human interaction and preserve health and well-being.
Ergonomic wrest rests can be part of an overall workstation design that
maximize HCI experience while minimizing chances for strain, stress, and
injury to EU.
B) Price – ?
Bureau of National Affairs. (1995). 770 percent increase. Occupational Safety and Health Reporter, 36, p.1794.
Granjean, E. (1987). Ergonomics in Computerized Offices. Taylor Francis: NY.
Helander, M. (Ed.). (1994). Handbook of Human-Computer Interaction. (4th ed.) North-Holland: NY, NY.
International Business Machines. (1991). Human Factors of Workstations with Visual Displays.(4th. Ed.). IBM: Somers, NY.
National Institutes for Occupational Safety and Health. (1997).
Musculoskeletal Disorders and Workplace Factors. NIOSH Pub No. 97-141.