So far, we spent a lot of time getting the details right for the best balance of leg strength in the chair and the best spine and torso postures, the arms are fully supported on the work surface, and the location of visual targets will preserve good head position. This is probably the best way to do multiple, mixed tasks on the work surface with short keyboard entries to the computer-there is still plenty of room to use the keyboard and the mouse and still rest the forearms with better posture.
At this point, we can raise the armrests to just graze under the work surface, so the chair and body can come close to the work surface for shorter reach and more support at the desk, but also have arm support as the chair moves away from the surface. If there is a conference call or some task that allows us to recline in the chair, then the body can relax with arm support on the chair.
The armrests can be very helpful, but there are several reasons they may not be the best support for keyboard use.
First, the armrest has a very small landing zone for the elbow, meaning the arm has only one small place to rest, which can restrict shoulder movement. Keyboard use means there is only one place to put the wrist, and those limits can make for awkward postures for the hand, wrist and shoulder.
Ideally, we have arm support on the work surface, enough room to move around the keyboard and mouse, and still have arm support when the chair moves away from the work surface.