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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

Workstation with Pull Out or Articulating TrayComfort
            Zone on a Workstation on a Desk What is Overreaching?

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 Zone. 

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 and tray). 

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 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)

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:
Conventional Keyboard Showing Reach for
              Mouse Due To Asymmetric DesignHow can a Keyboard Force a User to Reach Outside their Comfort Zone?

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 mouse. 

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 Deviation.

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 Pointing Devices and Touchpads will eliminate the need to over-reach when performing mousing activities.  Mice which require less physical space such as Touchpads, and Trackballs 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 Overreaching?

Keyboards which do not have a numeric keypad such as Adjustable Keyboards, Separated Keyboards, and Compact Keyboards 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 individual. 

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 height. If they are at different heights, by definition, one of them will be outside of the users Comfort Zone.

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 Keyboard Arm, or Adjustable Height Worksurface are other options to ensure the correct height. 

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

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


Last edited December 16th, 2013

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