If the design context includes what the person is doing as well as the things that they are using, the constraints need to include the way the human body works, or physiology, as well as the sizes of people.When you are designing a chair for work, you must consider the danger that long periods of sitting may cause back strain, which demands that you understand the structure of the human spine and the muscles that support it; this is not a constraint when you are designing a casual couch or a bar stool

Once we delve into the specifics of an active context like this, the designer may find that the issues are too complicated to understand and act on intuitively; this is when the partnership between designer and a human factors specialist, in these examples a physiologist, becomes essential.The basic complexity of design constraints still demands subconscious synthesis as well as collaboration between everyone in the multidisciplinary team, but a special connection is needed between designer and physiologist, to allow them to be innovative in the human aspect of the solution.