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Risk Factors and Sources of Injury > Overreaching Outside of the Comfort Zone          
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Overreaching Outside of the Comfort Zone

What is Overreaching?

Overreaching is when an individual has to reach outside their Comfort Zone to perform a task, such as mousing. The Comfort Zone refers to the area in front of them where they can comfortably reach and perform repetitive activities without moving their torso or experiencing discomfort. If a task requires movement and results in the body leaning forward and/or being bent at the waist, strain will be placed on the upper or lower back. This is overreaching outside of the Comfort Zone. This overreach forces the individual to adopt an awkward posture at the shoulders, elbows or torso, which can lead to strain and injury. 

What is a Comfort Zone?

People have both a Primary and Extended Comfort Zone. The Primary Comfort Zone is indicated in green in the image at right, and identifies the area that can be reached with the right upper arm in a relaxed position at the side. The green area can be comfortably accessed by rotating at the elbow. The Secondary Extended Zone is indicated in blue, and shows the area that can be reached by using the muscles in the left upper arm without over-exerting effort in those muscles. The blue area can be accessed, with some effort, by a combination of shoulder and elbow rotation. Any areas past these areas would be outside the Comfort Zone. 

The height of the worksurface can also affect Comfort Zone as if the worksurface is higher (or significantly lower) than the elbows, the user will have to compensate and overcome this height differential, greatly reducing their Comfort Zone.

Why is Overreaching a Risk Factor?

When an individual has to reach outside their Comfort Zone they must accomplish this by adopting potentially injury-prone postures in the upper extremities. This can be a combination of awkward movements of the wrist, elbow, shoulder and waist, since each person will use different combinations of movements to achieve the required extended reach. This will also 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 Deviation) or to the midline of the body (Radial Deviation). For the elbow this can be seen when abducting the elbow to the midline of the body (Medial Abduction) or to the outside of the body (Lateral Abduction). For the shoulder this can be seen when rotating the shoulder cuff to the front or back (Rotator Cuff Injury). For the waist, leaning forward or to the side will cause the individual to deviate from a orthopaedically sound S-Curve posture and adopt a C-Curve or other poor positions which will quickly fatigue muscles and lead to pain and discomfort. Regardless of how a person is able to reach past their Comfort Zone, these movements are not recommended as each one is a contributing risk factor which can lead to injury.

How do you Prevent Overreaching?

Restricting movements as much as possible to the Comfort Zone allows the individual to perform repetitive activities for a longer period of time without the immediate onset of fatigue, pain and discomfort arising from the location of the activity. Any potential risk factors arising from the 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.

Overreach of Comfort Zone Caused by Asymmetrical
          KeyboardWhat are the Causes of Overreaching?

This strain can arise from being forced to adopt an awkward posture at the shoulders, elbows or wrist. There can be many causes for overreaching, including:

How Can a Keyboard Force a User to Reach Outside their Comfort Zone?

Conventional Keyboard Showing Reach for
              Mouse Due To Asymmetric Design In most workstations the keyboard is rarely placed in a location which causes the user to reach outside their Comfort Zone.  However, conventional keyboards are inherently flawed because their layout directly causes varying degrees of overreaching for the mouse in nearly all deployments. What are these flaws? 
Unnecessary Distance: 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 arises from the layout including low frequency keys in the Comfort Zone.  Users are forced to reach over the arrow keys / navigation section of the keyboard, and a redundant numeric keypad to get to the mouse. Very few users need their high powered computer to act as a calculator in contemporary office environments.

Asymmetric Design: If one tries to reduce that reach by moving their body to the right, the second inherent flaw will undermine them. Traditional keyboards feature an asymmetric design that makes keying past the midline of the body even more awkward than overreaching for the mouse. Even moving the hands close to the midline of the body is a potential risk factor, as it forces the wrists into a position of Ulnar Deviation.
How Much Overreaching is "OK"?

Everyone has different levels of strength, dexterity, endurance and fatigue rates in their muscles, tendons and ligaments. 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 elbows into the sides) or 2" away from the body (i.e. distal, "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 or the back. The muscles across the back and in the shoulder blades will often exhibit symptoms of pain first as the weight of the arm when reaching "out" from the body is borne by these muscles. The muscles in the lower back will be affected first when a user leans forward or to the side because these muscles will immediately be tasked with keeping the individual upright without the support of the spine. Typically the pain experienced is a sharp burning pain, which slowly abates when awkward posture is abandoned.

How Does the Choice of Mouse Help to Reduce Overreaching?

Mousing Devices such as Central Pointing Devices and Touchpads which can be placed in front of the keyboard (i.e. in front of the space bar) instead of the traditional location beside the keyboard will eliminate the need to overreach when performing mousing activities. Mice which require less physical space for a full range of movement and/or can be controlled by the fingertips such as Touchpads, Trackballs and Fingertip Mice will reduce the range of movement to perform mousing activities and can also assist to a degree.

How Does the Choice of Keyboard Help to Reduce Overreaching?

Keyboards which do not have a numeric keypad such as Adjustable Keyboards, Separated Keyboards, and Compact Keyboards remove the numeric keypad from the keyboard and as such reduce the  reach to the mouse. These keyboards are more symmetrical than conventional keyboards (often nearly perfectly symmetrical) which brings the mouse into the Comfort Zone. 

Where should the Mouse and Keyboard be Located to be in the Comfort Zone?

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 must be located on the opposite side as the mouse. The keyboard and mouse must be at the same height. If they are at different heights, by definition, one of them will be outside of the Comfort Zone.

How Does the Choice of Keyboard Tray / Worksurface Help to Reduce Overreaching?

Keyboard trays and worksurfaces which are large enough to house both the keyboard and the mouse on the same surface and at the same height will reduce overreaching caused by the lack of sufficient space for the mouse on most standard keyboard trays. A standard conventional keyboard is 18" wide.  Most mice require a minimum of 6" of width (9" is strongly recommended) to allow a reasonable range or movement and acceleration setting (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. 

The input devices should be located at a height just above the lap, inline with the monitor so that the arms are slightly sloped downward (see graphic at right).  For adjustable height desks, simply lower the tabletop until it is at the appropriate height.

For fixed height desks, raise the chair until the top of the thighs are almost touching the underside of the desk, and place the keyboard and mouse on the desktop.  If this causes the legs to "dangle", a footrest should be employed to provide stability and comfort while working. If this is not a viable solution, an Articulating Keyboard Arm, or Adjustable Height Worksurface are other options to ensure the correct height. 

How Does the Choice of Book/Document Holder or Writing Surface Help to Reduce Overreaching?

Using a Document Holder, Book Holder, Writing Surface or Reference Organizer 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.


Last edited July 20th, 2018

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