Ergonomics

The relationship and interaction between people (aspects of the human body) and the products, systems and environments they use.

It makes a design more efficient, more usable, more functional, more effective and safer.

Comfort is only part of the people–product fit. A comfortable product can still fail the environment it is used in — for example a screen that is unreadable in sunlight.

The measurement of human physical dimensions, expressed as a percentile range, which presents the spread of physical characteristics across a population.

Static (structural) is measured with the body still — sitting eye height, popliteal height. Dynamic (functional) is measured while the body moves — forward grip reach, arm sweep.

Age, gender, ethnicity and disability. The age of the dataset itself matters too — populations have grown taller over recent decades.

The vertical distance from the floor to the underside of the knee when seated. It sets seat height, so that a user's feet rest flat and their thighs are not compressed.

The value below which a given percentage of a population falls. The 5th percentile of reach means 5% of people reach less far than that.

Reach is set from the SMALLEST user (5th percentile); clearance is set from the LARGEST user (95th percentile).

It fails half the population by construction, and nobody sits at the 50th percentile in every dimension at once. It suits only dimensions where being wrong either way is harmless.

90% of the user population. Covering the last 5% at each extreme usually costs far more in mechanism and tooling than it gains in users, so it is excluded as a stated decision.

Designing the product to be adjustable, and producing it in a range of fixed sizes. Many products use both.

Advantage: one product covers the whole 5th–95th range with one set of tooling. Disadvantage: the mechanism adds cost and weight, can fail, and only helps if the user actually adjusts it.

Advantage: each item is simpler, lighter and cheaper, with nothing to break. Disadvantage: several sets of tooling and stock, and the user must pick the right size.

A cycle helmet: two or three shell sizes keep each one light, and an adjustable cradle closes the remaining gap — a loose helmet does not protect in a crash.

The three-dimensional space a user can reach without moving from their position. Everything the product asks them to touch must lie inside it.

Normal reach is swept with the upper arm at the side and only the forearm extended — for constant and safety-critical controls. Maximum reach uses the whole extended arm — for occasional controls only.

Reach is sized from the smallest user, pulling surfaces lower and nearer; clearance is sized from the largest user, pushing them higher and wider. No single fixed geometry satisfies both, so the workstation adjusts.

Inside normal reach, however rarely it is used. Frequency sets the zone for ordinary controls, but a safety-critical control must be reachable instantly without stretching.

The study of the systems and biomechanics within the human body — their responses, limitations and capabilities. It tells a designer what a user can DO, where anthropometrics tells them how big the user is.

Visual accuracy, colour perception, strength, fatigue, muscle control and hearing thresholds.

Roughly 1 in 12 men has reduced red–green discrimination, so a colour-only code carries no information for them. Add a second channel — shape, position, a symbol, a pattern or text.

Fatigue lowers what the body can deliver as a task is repeated. A demand that sits just inside the limit for a rested user is outside it later in the shift.

The study of the human mind, including all the senses that send information to the brain — sight, sound, touch, smell and taste — and how they influence the design and development of products.

Smell: an odorant added to naturally odourless natural gas so leaks are detected. Taste: a bittering agent in detergent capsules so a child spits one out.

Carrying critical information through more than one sense — an alarm that both sounds and flashes. A single channel fails completely for part of the user group, while two degrade gracefully.

A flat screen gives no tactile detent, so the user has no confirmation that a press registered. Sound and haptics replace the feedback a physical button would have given by touch.