This mini-lesson covers Topic 1 — Human factors & ergonomics: how designers fit products to people using anthropometric data and percentiles, and how they account for psychological and physiological factors.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you are ready.
Ergonomics (human factors) is the study of how people interact with products, so designers can make them safe, comfortable and efficient. Instead of forcing the user to adapt, the designer fits the product to the person.
IB groups the influences on a design into three strands: anthropometric (body size), psychological (perception and the mind) and physiological (how the body copes physically).
Key idea: good ergonomics reduces error, discomfort and injury. Bad ergonomics shows up as strain, fatigue and accidents.
Anthropometrics is the collection of human body measurements. Static data is measured while the body is still (e.g. stature, hip breadth); dynamic (functional) data is measured while moving (e.g. reach, grip while turning).
Measurements vary across a population, so designers use percentiles. The 5th percentile is small (only 5% are smaller), the 50th is average, the 95th is large (only 5% are larger). Designing for the 5th–95th percentile range accommodates 90% of users.
Tap an item, then tap the group it belongs to.
Psychological factors concern how the mind perceives a product — through the senses. They include perception of colour, sound, smell, taste, light and temperature, and the product's aesthetics. These shape how a product feels to use.
Physiological factors concern how the body copes physically: comfort, fatigue and the limits of muscles, joints and senses over time. A control that needs high force, or a screen that causes eye strain, ignores physiological limits.
Watch out: percentiles alone don't guarantee a good product. Even a well-sized handle can be uncomfortable (physiological) or look cheap and untrustworthy (psychological).
Tap a statement on the left, then its matching term on the right.
Anthropometric tables list two kinds of measurement. Structural (static) data records the body at rest — stature, sitting height, hip breadth, hand length. Functional (dynamic) data records the body in action — forward reach, grip while twisting, the sweep of a working arm.
Designers pull these figures from validated datasets (national anthropometric surveys and tools such as ergonomic data tables), because measuring a full population yourself is impractical. The right choice of data depends on how the product is actually used.
Key idea: a control might fit a still hand (static) yet be unreachable mid-task (dynamic). Choose the data type that matches real use.
Designing everything for the "average" (50th percentile) user is a classic mistake: almost nobody is average in every dimension at once. A workstation set only for the average person is too high for the smallest and too low for the tallest.
That is why designers use the 5th–95th range and, wherever affordable, adjustability. Adjustable seats, steering columns and desks let each user tune the product to themselves.
Watch out: "design for the average" fails at the extremes. Design for the range, then add adjustment.
Ergonomics also governs the relationship between controls and displays. Good design uses clear affordances (a handle that says "pull"), sensible mapping (a dial that turns the way the value moves) and prompt feedback (a click, light or sound confirming an action).
When mapping is natural and feedback is immediate, users make fewer errors and learn the product faster — a direct ergonomic benefit.
Psychological factors are not vague — they can be designed deliberately. Colour signals meaning (red = danger, green = go); contrast and legibility decide whether a display can be read at a glance; sound and texture shape how premium or reassuring a product feels.
These perceptions affect real performance: a poorly contrasted warning label may be missed, causing a physiological or safety problem downstream.
Physiological limits set hard boundaries. Repetitive high forces cause fatigue and, over time, injury (RSI). Comfort depends on posture, support and the time spent using the product.
Designers reduce load by lowering required forces, supporting the body, allowing posture changes, and keeping frequent tasks within easy reach and view — the "comfort zone" of movement.
Key idea: ergonomics ties the three strands together — the right size (anthropometric), that feels right (psychological) and does not strain the body (physiological).
Ergonomics: designing products to fit the human body and mind.
Anthropometrics: static (still) and dynamic (in motion) body measurements.
Percentiles: 5th (small), 50th (average), 95th (large); design range 5th–95th covers 90% of users.
Clearance vs reach: clearance/access uses high percentiles; reach uses low percentiles.
Psychological factors: perception, aesthetics. Physiological factors: comfort, fatigue, body function.
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