On 23 August 2026 Yomif Kejelcha ran the Buenos Aires half marathon in 56:51 — the first legal “sub-57” in history and 29 seconds off Jacob Kiplimo's record. Almost immediately the running chats started arguing not about the Ethiopian's preparation, but about what he was wearing.

The reason is that in the spring, at the London Marathon, the same Kejelcha raced in a new adidas product — the Techfit Endurance Suit. The company claims the suit improves running economy by “more than 1%”.

What exactly is being claimed

One percent of economy is not one percent of time. The conversion gives roughly 0.67% of the result: about 48 seconds over a distance covered in two hours. For comparison: the carbon plate in racing shoes was worth around 4% in its day.

More important than the number is the mechanism being claimed. Aerodynamics would be the obvious guess: a tight suit, less flapping fabric, less drag. But adidas is not saying that.

The construction is a one-piece suit from shoulders to knees, with laser-cut tapes of thermoplastic polyurethane laid along it. Their job is to stabilise the pelvis and the hip joints. Jessica Hunter, who runs athlete services at the company, puts it plainly: you can only connect the torso to the pelvis with a single piece of clothing; split it into a top and shorts and you cannot.

So the suit is sold not as a fairing but as a soft exoskeleton: it is meant to stop your form from falling apart when the muscles holding the pelvis get tired. And it falls apart for everyone — in the third hour the pelvis drops, the stride shortens, the cost of a kilometre goes up.

Why to treat this carefully

The “more than 1%” figure is a manufacturer's claim. Not a peer-reviewed publication. Neither the sample size, nor the lab, nor the protocol, nor what exactly it was compared against — the team's normal kit or something deliberately bad — has been disclosed. We have been through this in the shoe industry: factory percentages and independent lab percentages rarely match.

Economy in the lab is not race time. The 0.67 conversion works on a treadmill at a fixed speed. In a marathon you also get heat, fuelling, tactics and precisely the degradation the suit was designed for.

The athletes themselves are split. The company describes the first reaction to the prototype bluntly: the runners laughed. Kejelcha eventually said he feels support in the hip and the back and wants to race in it. Sébastien Sauve, who trained in the suit, lined up on race day in ordinary shorts.

And the main thing the manufacturer stays quiet about is heat loss. A one-piece tight suit from shoulders to knees covers the surface through which sweat evaporates. In Buenos Aires it was +6 °C at the start — perfect conditions. What this suit does to thermoregulation in a marathon at +20 °C and high humidity has not been shown publicly by anyone. For an amateur running four hours rather than two, that is not a detail, it is the main question.

Incidentally, World Athletics does not specify what Kejelcha was actually wearing in Buenos Aires in its record report — so the suit theory for that race remains a theory from the chats, not a fact.

The regulatory hole

World Athletics regulates footwear in detail: sole thickness, number of plates, how long a model must be available at retail. Clothing it does not regulate at all.

The analogy suggests itself. In 2008 Speedo released the LZR Racer — a polyurethane suit in which dozens of world records were rewritten within two years. It ended with a ban on technologies that look modest by today's standards, and with years in which those records stood out of reach. Former Olympians are already urging the federation not to repeat the plot and to deal with clothing in advance.

The difference is that the LZR gave buoyancy and reduced water resistance — a direct, measurable effect. Here the claimed effect is second order: not “pushes you forward” but “stops you breaking down”. Regulating that is incomparably harder.

What this means for an amateur

There is nothing to buy. The suit exists inside elite contracts; it is not sold at retail as a mass product.
The idea transfers, the garment does not. If the 1% comes from pelvic stability under fatigue, then for an amateur the same percent sits in strength work for the glutes and in running on top of fatigue — and it costs less than any suit.
Tight clothing on its own will not give you a percent. Compression tights and a lycra race suit are not Techfit; the claimed effect is attributed to specific polyurethane tapes in specific places.
In the heat a one-piece suit is a risk, not an advantage. Until there is data on heat loss, for races warmer than +15 °C this is a blind bet.

Key points

On 23.08.2026 Kejelcha set the half marathon world record — 56:51 (previous: 57:20, Kiplimo), at +6 °C and with a tailwind on part of the course.
adidas claims the Techfit Endurance Suit delivers more than 1% of running economy — about 48 seconds over a two-hour marathon.
The mechanism, according to the manufacturer, is not aerodynamics but stabilisation of the pelvis by thermoplastic polyurethane tapes.
The figure is not confirmed by an independent peer-reviewed publication; the protocol and sample have not been disclosed.
Athlete reaction is mixed: Kejelcha raced London in the suit, Sauve turned it down on race day.
World Athletics regulates shoes but not clothing — the LZR Racer precedent in swimming ended in a ban.
The open and undiscussed question is thermoregulation: a one-piece suit covers the evaporating surface.

Sources: World Athletics, half marathon world record report, Buenos Aires, 23.08.2026. https://worldathletics.org/competitions/world-athletics-label-road-races/news/world-half-marathon-record-buenos-aires-2026-yomif-kejelcha · LetsRun, «Adidas claims new speedsuit used in sub-2 hour London Marathon improves running economy by more than 1 percent», May 2026 · Marathon Handbook, «Adidas Built A Suit That Makes You Run Faster», 2026