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Risk Factors and Sources of Injury > Supination as a Risk Factor         
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Supination as a Risk Factor

What is Supination?

Supination refers to the twisting of the forearm and the corollating orientation of the hand towards a "palm up" orientation.  When the hands and forearms are flat on a desk, such as when working on a conventional "flat" keyboard or "flat" mouse, they have fully "pronated" their hands and forearms. For most individuals, the posture that is most comfortable is somewhere between 10° from the horizontal (i.e. with the thumb side of the hand higher than the little finger) and a vertical or "handshake" position (i.e. 90° from the horizontal). Due to physiology, past injuries, or developed conditions each individual will have their own unique range of comfortable postures.  Most people find some amount of pronation to be the most comfortable position; very few people find any amount of Supination to be ideal or even tolerable for an extended period. 

Why is Excessive Supination a Risk Factor?

When an individual forces their hands to supinate, a Static Load and strain is placed on the joints, muscles, ligaments and membranes in the arm. That can lead to fatigue, discomfort, pain and eventually injury. Just as supination is something that individuals seeking to reduce the risk of injury should avoid, excessive Pronation (rotating the forearm and hand past a vertical orientation towards a palms-down orientation) can be an equally significant risk factor.

What is the Best Angle to Position the Hand and Forearm?

As indicated earlier, each individual is unique and for some, a near vertical posture will be most comfortable while for others a near horizontal posture will be ideal. Unfortunately, there is no "best" angle for everyone, and there are multiple factors that need to be considered since what may be the best angle for the elbow may not be for other muscle groups (e.g. the fingers). For keyboarding, the tradeoffs of increasing the angle beyond 20° typically make this the maximum viable angle to ideally position the keyboard for most users (see Why Does Vertical Mousing have Fewer Drawbacks than Vertical Keyboarding). For mousing, there are not always tradeoffs in moving to a more vertical posture, which makes mice up to 30° a good option for almost all users, and mice up to 90
° an option worth considering for many users

Last edited July 17th, 2018

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