Outside of the Comfort Zone
Overreaching occurs when a person has to reach outside their
Comfort Zone to perform a task, such as mousing. The
Comfort Zone of an individual refers to a prescribed physical
area where they can comfortably reach and perform repetitive
activities without excessive strain. This strain can arise
from being forced to adopt an awkward posture at the shoulders,
elbows or wrist. When an individual has to reach past this
immediate 'green zone' defined by the arcs of a minimal (10°
swivel) at the elbow, they are over-reaching their Comfort
If the task requires movement causing the body to 'bend' at the
waist, placing strain on the upper or lower back, that is
outside of the individuals Comfort Zone. The height of the
work surface is also crucial as it should be no higher than the
elbows of the individual (and preferably slightly lower,
especially if the work is being performed on a secondary work
surface such as the case with deployments of an articulating arm
Why is Overreaching a Risk Factor?
When an individual is required to reach outside their Comfort
Zone they must achieve this by adopting potentially injury-prone
postures in the upper extremities. This can be a
combination of twists in the joints of the wrist, elbow and
shoulder in either direction, as different individuals will use
different combinations of movements to achieve the required
extended reach. In addition, this will increase the
demands on muscles to perform in a non-optimized manner,
resulting in overexertion and strain.
For the wrist this can be seen when twisting laterally to the
outside of the body (Ulnar
) or to the midline of the body (Radial
). For the elbow this can be seen when
abducting the elbow to the midline of the body (Medial
) or to the outside of the body (Lateral
). For the shoulder this can be seen when
rotating the shoulder cuff to the front or back (Rotator Cuff
Regardless of what combination of joints is used, these postures
are not recommended as each one is a contributing risk factor
which can lead to injury.
Restricting movements as much as possible to the Comfort Zone
results in the user becoming less fatigued. Any potential
strain and fatigue arising from the specific activity itself
will now become the sole risk factor for performing that
activity. An individual will always be able to reduce
their risk of injury whenever they are able to avoid reaching
beyond their Comfort Zone.
What are the Causes of Overreaching?
There can be many causes for overreaching, including:
How can a Keyboard Force a User to Reach
Outside their Comfort Zone?
- Insufficient space
on a pull-out or articulating tray to accommodate the mouse,
with the result that the mouse is on a different surface
(for example on the desk underneath the monitor, and/or at a
higher elevation to the left or right of the keyboard tray).
- Asymmetrical keyboards which create a larger reach for
tasks on one side of the keyboard than the other. This
is usually caused by the presence of a redundant numeric
keypad which is normally needed by less than 1% of users
is a Discrete Numeric Keypad Appropriate?)
- Conventional keyboards which cause the user to reach into
- Repositioning and/or writing on reference material
For most individuals, the keyboard itself is rarely placed
in a location in their workstation which causes the user to
reach outside their Comfort Zone. However, due to the
inherent flaws with conventional, traditional keyboards the
layout causes overreaching for the mouse in the majority of
deployments. There are two reasons for this, the first
which is clearly shown in the image at right. For a right
handed user on a traditional keyboard, the reach for the mouse
from the right hand home row position is well over a foot (over
30 cm)! This is caused by being forced to reach over the arrow
keys / navigation area and the numeric keypad to get to the
If a user attempts to reduce that reach by moving to the right,
the second reason will undermine them. Conventional
keyboards feature an asymmetric design which makes keying past
the midline of the body even more awkward than overreaching for
the mouse. In reality, keying anywhere near the midline of
the body is also a potential risk factor, as it leads to Ulnar
How Much Overreaching is 'ok' and not a Risk Factor?
Every individual has different degrees of strength, dexterity,
endurance and fatigue rates in their muscles, tendons and
ligaments in their upper body. For most individuals, a
minimal abduction of the elbow or wrist is usually not
sufficiently severe enough to cause pain or discomfort and may
not be a risk factor. For most users, any movement of more
than 1" of the elbow towards the body (i.e. proximate or pushing
into the side of the individual) or away from the body (i.e.
distal or 'winging' or appearing to start to do the movements of
the "Chicken Dance") is a significant risk factor.
What are the Symptoms of 'too much' Overreaching?
Common symptoms are pain in the wrist, the elbow, the shoulder
(in other words, all the affected joints). In addition,
the muscles across the back and in the shoulder blades often
will exhibit symptoms of pain as the weight of the arm when
reaching 'out' from the body is borne by these muscles.
Typically the pain is a sharp burning pain, which slowly abates
when awkward posture is abandoned.
How can the Choice of Mouse Help to Reduce Overreaching?
Mice which can be located below the keyboard instead of to the
side such as Central
will eliminate the need to over-reach when performing mousing
activities. Mice which require less physical space such as
will reduce the range of movement to perform mousing activities
and can help to a small degree.
How can the Choice of Keyboard Help to Reduce
Keyboards which do not have a numeric keypad such as Adjustable
, and Compact
remove the need to reach over a numeric keypad
to reach the mouse. In addition, these keyboards are
symmetrical which bring the mouse closer to the midline of the
Where should the Mouse and Keyboard be Located to be in the
Comfort Zone of a User?
The keyboard and mouse should be placed so that the user does
not have to overextend themselves when reaching for either
device. The mouse should be located immediately to the
left or right of the keyboard, and if a numeric keypad is
required, it should be located on the opposite side as the
mouse. The keyboard and mouse must be at the same
. If they are at different heights, by
definition, one of them will be outside of the users Comfort
How can the Choice of Keyboard Tray / Worksurface
Help to Reduce Overreaching?
Keyboard trays and worksurfaces which are of
sufficient area to allow the keyboard and the mouse to be
located on the same surface at the same height will reduce
overreaching caused by insufficient space for the mouse on
smaller keyboard trays. A standard conventional keyboard
is 18" wide. At a minimum 6" of lateral room for the mouse
is needed (9" is strongly recommended to allow a reasonable
mouse acceleration (see Setting
Mouse Acceleration at an Optimal Level for the Task
This means that for most users the smallest width of keyboard
tray that should be considered is 27" wide.
This should be located at a height
just above the lap of the user
, inline with the
monitor. The easiest means to accomplish this is to raise
the chair until the top of the thighs of the user touch the
underside of the desk, and place the keyboard and mouse on the
desktop. If this causes the legs of the user to 'dangle',
a footrest can be used to provide stability and comfort while
working. If this is not a viable solution, an Articulating
, or Adjustable
are other options to ensure the correct
How can the Choice of Book/Document Holder or
Writing Surface Help to Reduce Overreaching?
Using a Document
, or Writing
which can be located inline (i.e. above the
keyboard and below the monitor, directly in front of the user
instead of to the left or right) will position materials closer
to the comfort zone of the user.