How do Office chairs and tables designed from the ergonomic point of view?

Your desk is a critical component of your workstation. It supports tasks (writing), above-surface equipment (computer monitor, phone, etc.), and below-surface equipment (keyboard tray system or CPU holder). The height and layout of your work surface play an important role in your work posture and efficiency. A good ergonomic arrangement is one that will allow you to work most efficiently in a good posture.

You should be able to sit comfortably in the chair, using as much of the chair back as possible for support. The lumbar support should fit comfortably into the curve of your lower back, and your feet should be flat on the ground (use a footrest if necessary). The seat pan (i.e. the part on which you sit) should be an appropriate size that allows at least one inch between your legs and either side of the chair, and supports your legs without applying pressure to the back of your knees.

Sources:
http://www.healthycomputing.com/office/setup/desk/index.html http://www.healthycomputing.com/office/setup/chair/index.html