MYP Design Ergonomics and Comfort Notes

Ergonomics Fits the Product to the Body

1. Ergonomics is the work of shaping a product around how a body sits, stands, grips and moves, so using it does not hurt after twenty minutes.
2. It is one of the MYP design related concepts, and it shows up in almost every product brief where somebody has to hold, wear or sit in the thing you make.
3. A product can hit every size on the drawing and still be badly shaped, like a suitcase handle that is the right height but cuts a ridge into your palm.
4. Comfort is not a soft extra, because an uncomfortable tool gets put down, held wrongly or modified with tape by the person who has to use it all day.

Ergonomics and anthropometrics do different jobs

1. Anthropometric data gives you the sizes, and a separate article covers percentiles, clearance and reach in detail.
2. Ergonomics then decides what to do with those sizes: the angle of a handle, the softness of a grip, how much a lever should resist.
3. So a scissor handle sized on 5th percentile hand length is anthropometrics, and cushioning the loop so it stops cutting into the finger is ergonomics.

Posture Decides How Long Someone Lasts

1. A neutral posture keeps the spine in its natural S curve, the elbows near 90 degrees and the wrists straight, and every degree away from that costs energy.
2. Work held above shoulder height tires the arm fastest, which is why a painter on a roller extension pole gets more done than one on a short brush.
3. Static loading is holding one position without moving, and it fatigues a muscle faster than the same effort spread over movement, because the blood supply gets squeezed.
4. That is why a stool with no backrest is fine for five minutes at a workbench and miserable for an hour.
5. Lumbar support pushed into the small of the back at around 230 mm above the seat keeps the pelvis from rolling backwards, which is what turns a straight back into a slump.

Grip and Reach Zones: Where the Hand Can Actually Work

1. A power grip wraps the whole hand around an object, thumb overlapping the fingers, and it is what you use on a hammer, a kettle handle or a bike grip.
2. A precision grip pinches between thumb and fingertips for control, as on a pencil, tweezers or a small dial, and it is far weaker.
3. A pinch between thumb and finger produces roughly a fifth of the force of a full-hand grip, so never ask a pinch grip to do a power job like opening a stiff valve.
4. The normal working area is the arc the forearm sweeps with the upper arm hanging down, about 350 mm to 450 mm from the shoulder, and constantly used controls belong inside it.
5. The maximum working area is the full arm sweep, roughly 600 mm to 700 mm, and it suits things touched a few times an hour rather than a few times a minute.
6. Anything that must be grabbed in an emergency, like a machine stop button, goes in the normal zone even if it is almost never pressed.

Force: How Hard Should a Control Be to Push?

1. Every control needs enough resistance that it is not triggered by accident and little enough that the weakest intended user can work it.
2. A keyboard key takes around 0.6 N, which is light enough for hours of typing, while a fire door should open with no more than about 30 N at the handle edge so a child or an older person can get out.
3. Size the force on the weakest user you intend to serve, not on yourself, because a fit 15 year old squeezing a trigger tells you almost nothing about a grandparent with arthritis.
4. Torque matters as much as push force, and a jar lid is easier because the ribbed edge gives a wider grip radius, turning the same hand force into more twist.
5. Give the control feedback so the user stops pushing: a click, a detent, a change in resistance at the end of travel.

Repetition, Vibration, Heat and Noise Are Slow Damage

1. Repetitive strain injury builds from four things together: a repeated movement, force, an awkward joint angle, and no recovery time between repeats.
2. The classic design fix is to bend the tool instead of the wrist, which is why a good soldering iron or a pistol-grip drill puts the handle at an angle to the shaft.
3. A spring that returns a trigger or a stapler for you removes half the repetitions, because the user no longer has to pull it back.
4. Vibration from an angle grinder or a hammer drill damages the nerves and blood vessels in the fingers, producing the numbness and whitening known as hand-arm vibration syndrome.
5. Heat travels through a handle at a speed set by the material, so a steel saucepan handle burns while the same shape in phenolic plastic or bakelite stays touchable.
6. Noise above roughly 80 dB over a working day starts to damage hearing, and a quieter motor, a rubber mount or a damped panel is a better answer than handing out earplugs.

Testing Comfort Needs Real Users Over Real Time

1. Almost anything feels fine for thirty seconds, so a comfort test has to run long enough for fatigue to appear, which usually means 20 to 30 minutes of the actual task.
2. Test with the people who will use it, because your own hand is trained on your own prototype and will forgive things a stranger will not.
3. A body map is a simple outline of a person that testers shade where it aches, and it locates a problem far better than asking whether the product was comfortable.
4. Ask for a discomfort rating from 1 to 5 at the start, the middle and the end, so you can see the curve rather than one final number.
5. Watch as well as ask, because users shift grip, rest the tool on a knee or shake out a hand long before they say anything hurts.
6. Test with the same gloves, sleeves or wet hands the real situation involves, since a grip that works dry can be useless in a kitchen or a workshop.