With wrist extension, your wrists are bent up and back such that the fingers are higher than the wrist joint. This greatly reduces blood circulation through the wrist and hand and can quickly cause pain, fatigue and numbness. Most traditional keyboards have a positive 10 degree slope from front to back that promote wrist extension. Unfortunately most keyboard users do not demonstrate perfect keying technique, but rather drop their wrists into a dangerously extended posture over the front edge of the keyboard and onto the work surface.

Solution
In order to reduce/eliminate wrist extension Kinesis contoured keyboards have integrated palm supports that positions your wrist in a neutral position - at the same elevation as your forearm and hand.