Seated movement, and why five variants or it does not ship
Seated movement and three other variants are authored independently, never degraded from the standing one. Five or it does not ship, and there is no override.
What a mode changes
Accessible interface design here starts from a verified age band and a capability profile. Mode is not a preference and it cannot be chosen freely, because it governs safeguarding rules rather than taste.
Between Explorer at ten and Vitality at ninety, the following all change: interface density and target size, the coach's register and vocabulary, which gamification mechanics are legal, what data may be collected at all, which clinical guardrails apply, and the default movement variant.
A ten-year-old and an eighty-eight-year-old are not the same person with different eyesight. Treating them as such produces an interface that patronises one and exhausts the other.
The mechanics that are illegal by mode
Competitive leaderboards do not exist below 18. Loss framing does not exist anywhere. Body metrics do not exist below 18 and are opt-in above it. Public visibility of another person's activity requires a mode that permits it, and two of the six do not.
Because these are enforced per mode rather than per feature flag, adding a new mechanic means declaring which modes it is legal in. There is no default of "all".
Minimum sizes are not a setting
Body text is 16 pixels in the middle modes, 18 in Independence and 20 in Vitality — as a floor, not a starting point a user drags. Touch targets go from 48 pixels to 56 in later life, against a WCAG minimum of 24.
The reason to bake this in rather than expose it: the person who most needs the larger target is the person least likely to go looking for the setting that provides it.
The cost
Six times the review surface on every screen — accessible interface design costs this much when it is real. Every component takes mode as an input and every design review looks at six states. It is slower and it is not optional — a product for ages ten to a hundred that only really works for one of those decades is a product for one of those decades.
What changes between two adjacent modes
Balance covers 40 to 64 and Independence covers 65 to 79, which sound close and are not. Balance defaults to standing variants and treats a chair as an option. Independence defaults to chair-supported and treats standing as something to be chosen. That single default is the difference between an app that assumes you are fine and one that assumes nothing.
The coach's register changes too. In Balance it is direct and slightly terse, because the research on that age band is unambiguous that people find encouragement patronising. In Independence it is warmer and states the safety point explicitly rather than leaving it implied, because the consequence of a misjudged movement is materially different.
Data collection narrows as well. Independence and Vitality collect less, not more, despite the clinical case for collecting more being stronger. The reasoning is that the people most likely to be harmed by a breach are the people least able to recover from one.
Why mode is not a user setting
You can change your capability profile, your goals, your notification preferences and the coach's presence level. You cannot change your mode, because mode is derived from a verified age band and it governs which safeguarding rules apply.
The obvious objection is that a fit 70-year-old is being patronised by Independence defaults. They are not, because capability is a separate input: the mode sets the safeguarding floor and the capability profile sets the difficulty. A very fit 70-year-old gets hard movements with a chair available and no leaderboard.