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The Permitted Field
// 2021–2026 — a ban written for two molecules meets an industry that shipped four more it never named
In 2021, the UCI did something it had never done before: it named two specific physiological measurements and made them illegal to monitor in real time during a race. Glucose and lactate — the two clearest windows into how close a rider's body is to running out of fuel — were banned under rule 1.3.006bis, closing off a category of data that devices like Supersapiens had only just made practical to wear.
It was a narrow rule, aimed at a narrow problem: two named substances, one clear line. It did not ban physiological monitoring in general. It banned glucose and lactate, specifically, because those were the two technologies that existed at the time the rule was written.
Five years later, the industry answered with a list of things the 2021 rule had never named. Wahoo's most recent bike computer update added native support for four new physiological data streams: core body temperature and heat strain index, breathing thresholds, sweat and sodium loss, and electrolyte analysis. Every one of them is currently legal — not because the UCI reviewed them and approved them, but because nobody had written a rule against them yet.
Here's the interpretive claim, stated plainly so it isn't mistaken for a documented fact: the UCI's rule is built as a blacklist, not a whitelist. It bans specific named categories one at a time, after they already exist, rather than defining a closed set of data types that are legal and treating everything else as prohibited by default. That structural choice — ours to point out, not the UCI's to have stated — is what turns this into a permanent design gap rather than a one-time oversight. Every new sensor category gets a free runway for however long it takes someone to notice, name it, and write the next rule.
The bike computer size cap set to take effect in 2028 is the clearest evidence that the UCI itself sees the shape of this problem, even without solving its root cause. A hardware-level limit on screen size is a blunt instrument — it doesn't touch what data a device can collect, only how much of it a rider can see mid-race. It's a sign the arms race has gotten physically large enough to legislate against, years after the underlying data race began.
The 2021 ban, the 2026 sensor update, the July 2026 pocket ban, and the 2028 size cap are all independently documented and dated. The claim that this amounts to a "blacklist instead of a whitelist" design failure is our read, not a position the UCI has stated. It's the most reasonable interpretation of the pattern, not a quoted admission.
The 2021 origin of UCI rule 1.3.006bis and its glucose/lactate prohibition are drawn from Cycling Weekly's contemporaneous reporting on metabolic sensor bans, treated as Tier 2 secondary confirmation of the rule's existence and scope. The 2026 Wahoo sensor update — core temperature, breathing thresholds, sweat/sodium, and electrolyte tracking — and the July 2026 front jersey pocket ban are drawn from the5krunner's coverage, treated as Tier 1 industry trade reporting. The UCI's current permitted data fields (heart rate, body temperature, sweat rate) and the glucose/lactate prohibition are corroborated by Cyclingnews's reporting on the same rule, treated as Tier 1. The 2028 bike computer size cap and the jersey pocket exception for radio devices are drawn from Domestique Cycling's reporting, treated as Tier 1.
The sensors are legal. The next question is what teams actually do with everything they collect. Post II, The Random Forest, is documented too — a model that's been quietly running in Tour de France broadcasts since 2019.
