Audit Record — The 40mm Line

For most of the sport’s history the rulebook of world athletics capped the sole of a high jump shoe at thirteen millimetres, and set no limit at all on the sole of a marathon shoe. The shoe worn for two seconds was regulated. The shoe worn for two hours was not.

Nothing in this case was concealed and no rule was broken. Every shoe in it is on a public list, approved, and legal. This record is the working behind the audit: what the governing documents say, where each number comes from, and — set out explicitly at the end — what this record does not claim.

The governing text, before the limit

The Technical Rules in force from 1 November 2019 addressed sole thickness under Rule 5.5. In the High Jump and Long Jump the sole was capped at a maximum thickness of 13 mm, and the High Jump heel at a maximum of 19 mm. The rule then closed:

In all other events the sole and/or heel may be of any thickness.

The marathon is one of those other events. The clause is not an oversight in the drafting; it is the operative text, and it stood while the shoes that would later prompt a limit were being developed.

The assumption inside it was that sole material absorbs energy rather than returning it. Once foam and embedded geometry could return a meaningful fraction of what they absorbed, “any thickness” stopped describing a comfort feature and started describing a design allowance without a ceiling.

The limit arrives

On 31 January 2020 World Athletics announced a modification to the rules governing competition shoes, citing research by its Assistance Review Group. That research is referred to in the announcement and is not linked to it.

The permanent, event-by-event text followed as an amendment to Rule 5, approved 15 July 2020 and effective 28 July 2020:

Announcing the table, World Athletics’ chief executive described the basis for the figures in the accompanying release: the organisation had a better understanding of what technology was already in the market, and of where the line needed to be drawn to maintain the status quo.

That is the stated rationale, in the governing body’s own words, and it is worth reading precisely. It describes a limit set to preserve an existing state of affairs, not one derived from a threshold of unfair advantage.

How the limit is measured

The Athletic Shoe Regulations effective 1 January 2026 define the measurement. Regulations 8.3 and 8.4 specify that thickness is taken as the distance between the inside top side of the sole and the plane of its outside under side, with the shoe placed on a hard flat substrate — measured at two named locations:

• The centre of the forefoot — the centre point of the shoe at 75% of its internal length.
• The centre of the heel — the centre point of the shoe at 12% of its internal length.

Two coordinates. Not the thickest point of the sole, not a mean thickness, not a profile. A sole has thickness at every point along its length; the regulation caps it at two of them.

The tolerance, and where it applies

Regulation 8.4.2 grants a measurement tolerance of 5% — one millimetre on twenty, two millimetres on forty. Its scope is written into the same clause, and the scope is the point:

For the purposes of Regulation 12.3, where an Athletic Shoe has been submitted for examination and investigation by the Independent Body…

At approval, the regulation is flat: the sole must be at or under forty millimetres, and no tolerance is offered anywhere in that process. The 5% appears once in the document, and only for a shoe that has been taken in for examination. The only shoe ever measured against forty-two millimetres is a shoe that has already been pulled out of a competition.

The allowance is not granted to the field. It is granted to the one shoe under suspicion.

What shoe control actually does

The Shoe Control Guidelines, effective 1 January 2026, describe the procedure applied at competition. On the question of measurement they are explicit:

To be clear, no sole thickness measurements are expected to be conducted during shoe control.

What happens instead is a match: an official identifies the shoe by brand, model name and/or model number, and checks that identification against the list of approved shoes. The guidelines then set the condition for escalation — if the shoe is on the list and the athlete did not achieve a world record, no further action is required. Where that condition is not met, the shoe is collected and sent to an independent body for further examination.

Read the structure of that sentence. The trigger for examining a shoe is not a doubt about the shoe. It is the athlete’s result.

The register

The list against which the check is made records shoe company, model, type, and a yes or no against each event category, with the applicable thresholds set out in the header row and the approval’s start and end dates alongside.

It records approval. It does not record thickness. There is no measured dimension in any column.

Provenance note: the edition examined for this audit is the World Athletics Shoe Compliance List dated 19 February 2021, cross-checked against the 25 January 2021 edition; the two agree. That PDF has since been retired in favour of a Shoe Check Application, whose fields could not be inspected because the site disallows automated access. The register’s current structure is therefore unverified and is presented in the audit as the 2021 edition. The finding does not rest on it — it rests on the Shoe Control Guidelines, which are current, and which describe matching a shoe by brand and model whatever form the list is served in.

The chain, in one pass

1. The rule states a maximum of 40 mm.
2. The written procedure measures that maximum at two coordinates, and forgives two millimetres of it — but only once a shoe is already under independent examination.
3. The field procedure measures nothing.
4. The register records a name.

Four documents, and at no point in any of them is the shoe on the athlete’s foot a measurement.

Sources

All are World Athletics primary documents unless marked otherwise.

• Technical Rules (C2.1), in force 1 November 2019 — Rule 5.5, the 13 mm / 19 mm caps and the “any thickness” clause.
• Press release, 31 January 2020 — World Athletics modifies rules governing competition shoes for elite athletes. The moratorium; the reference to Assistance Review Group research.
• Amendment to Rule 5 of the Technical Rules — approved 15 July 2020, effective 28 July 2020. The event-by-event table.
• Press release, 28 July 2020 — World Athletics amends rules governing shoe technology and Olympic qualification system. The “maintain the status quo” wording.
• Athletic Shoe Regulations (C2.1A), effective 1 January 2022 — the intermediate edition.
• Athletic Shoe Regulations (C2.1A), effective 1 January 2026 — Regs 8.3, 8.4, 8.4.2, 8.5. The clauses quoted above.
• Athletic Shoe Regulations (C2.1A), effective 20 April 2026 — a later edition, approved 19 March 2026. Every clause quoted in this record is unchanged in it.
• Shoe Control Guidelines, effective 1 January 2026 — the competition procedure and the escalation condition.
• World Athletics Shoe Compliance List, 19 February 2021 — the register’s column structure.
• Marathon world record progression, men’s senior, ratified — World Athletics records, used only as a plotted baseline.

Open items

• The Assistance Review Group research is not public. It is cited in the January 2020 announcement and not published alongside the rule it produced. Searches return independent peer-reviewed literature on advanced footwear technology, but no research published by World Athletics as the Group’s own. Absence from search is not proof of non-existence; the claim here is scoped to what can be stood behind — that it was not published with the rule.
• The current approved-shoe list is unverified. See the provenance note above.
• World Athletics has not been asked to comment on the reading of Regulation 8.4.2’s scope set out here.

What this record does not claim

It does not claim that the forty-millimetre limit was set for any particular shoe. No World Athletics document says that. The chief executive’s explanation of the figures and the reported stack height of any given shoe are two separate facts, and they are kept separate here.

It does not claim that shoes are never measured. An escalation to independent examination exists and is written into the regulations.

It does not claim that any rule was broken, by anyone. No athlete is accused of anything. No manufacturer is accused of anything. The finding is that routine shoe control verifies a name rather than a dimension — narrower than a violation, and harder to correct than one.