Physiology informs design constraints by explaining how the human body functions during an activity, complementing anthropometric data about body dimensions. For example, designing a work chair requires considering how prolonged sitting affects the spine and supporting muscles. When these interactions are too complex to evaluate intuitively, designers should collaborate with human-factors or physiology specialists while integrating their findings with the multidisciplinary design process.

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According to Bill Moggridge in *Designing Interactions*, the **hierarchy of complexity** of design constraints consists of six disciplines that designers must navigate as products and systems become more complex:

1. **Anthropometrics**: Focuses on the physical dimensions and sizes of people.
2. **Physiology**: Focuses on how the human body works and its mechanical functions.
3. **Cognitive Psychology**: Focuses on how the mind works and processes information.
4. **Sociology**: Focuses on how people relate to and interact with one another.
5. **Cultural Anthropology**: Focuses on the human condition, cultural variations, and societal contexts.
6. **Ecology**: Focuses on the environmental impact and interdependence of all living things.

As a design problem moves from simple physical interactions to complex, systemic service ecosystems, the constraints increase in complexity, requiring collaboration with specialists from these respective fields.

Hierarchy of Complexity of Design Constraints

The constraints are complex enough to demand the core skills of
design, but the problems are well understood and have been
evolving slowly since industrial design emerged as a new
discipline in response to the Industrial Revolution.

Human factors work at the office of Henry
Dreyfuss, anthropometric information for the designer is easy to
find, by referring to the book The Measure of Man, or the
reference cards in Humanscale, which present the salient
dimensions of people of different statures, gender, age, and ethnic
background.

Anthropometrics

Hierarchy of Complexity

When you are concerned about the constraints that will
matter to people when you are designing computers and things
that are enhanced by electronic behaviors, you need a much more
rigorous understanding of the way the mind works. When the
design context includes machine intelligence as well as human
intelligence, the design team will benefit from the expertise of a
cognitive psychologist and will also need designers who are
skilled at designing interactions.

Cognitive psychology

Sociologists can help members of a design
team understand the implications of this and to operate in the
more abstract realm of designing services, where you are affected
more by relationships among people as well as between users and
objects or interfaces. Although services have been around for a
long time,the sudden expansion of technology enabled services—
and hence service design as a discipline—is still very new

The addition of the expertise of sociologists to a design team
is especially important when the nature of the constraints is
systemic.When we are designing connected systems of products,
services, and spaces, which are used in real time, the brain of any
designer who tries to absorb all of the constraints is likely to
explode. We are better equipped to face the complexity as an
interdisciplinary team, with a collective consciousness, and the
ability to create designs as a group or team rather than as
individuals.

Design Science and Sociology

Sustainable design can seem in direct opposition to the consumer society that designers enhance, making it a challenging subject. Increasingly, organizations and processes emerge to help design teams analyze the sustainability of their designs, including material use, energy, and the "cradle to cradle" lifecycle. However, this knowledge is still immature, making sustainable design an intuitive rather than exact science. While designers can intuitively synthesize complex requirements, they still require solid information to draw on since sustainability science is not yet well established.

Ecology in Design

Physiology in Design

Cultural anthropologists can help people in a development organization understand the nature of cultural differences, which probably will not be intuitively obvious to them without some direct experience of the variations. There are also variations of culture within a single market, as different groups of people have unique anthropological characteristics, based on their occupation, background, or
interests.

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