Attempting to just do it

Ever since Nike announced a campaign to break the two-hour barrier in the marathon in December last year, it was inevitable that a shoe would be central to the attempt.

Short of running the marathon downhill with a giant fan blowing the runners along from behind, shoe technology was the only way the two minutes and 57 seconds needed to break two hours would be found.

Confirmation came last week when Nike revealed the specially designed shoe that will be used in the attempt.

Two months ago, I wrote that in order to achieve the sub two-hour goal, Nike would need to go beyond incremental advances and find something profound, revolutionary.

This would have to involve a shoe that functioned like a spring, giving the runner a significant increase in energy return on every stride.

That shoe now has a name - the Nike Zoom Vaporfly Elite. A combination of a curved carbon fibre plate inserted into the midsole and a new cushioning material are said to return 13% more energy than conventional shoes and, as a result, lower the oxygen demands of the runner by 4%.

That's potentially significant because lower oxygen demand implies less energy is being used, and this matters because the complex physiology that gets energy to muscles sets the limit for marathon-running performance.

I'm not entirely convinced it works as promised, but hype leads to hope, and this shoe offers both.

Historically, the arrival at this point has been inevitable ever since Oscar Pistorius appealed to run in able-bodied races, and scientists evaluated his hi-tech carbon fibre prosthetic blades. It was obvious to me that the combination of the material - very stiff carbon fibre - and the shape - curved to compress when landing and then to "recoil" by releasing that compression to propel the runner forward - would provide a significant energy advantage to any user skilful enough to use the "tool".

The challenge has always been getting those concepts into a normal running shoe, rather than in long, unstable prosthetics. Other shoes have tried the carbon fibre plate approach to increase stiffness, but that alone isn't enough. It helps a little bit - 1% according to one study - but the real benefit would come from recoil over and above a stiffer shoe.

At this point, remove from your mind the idea that a spring looks like a pogo stick, because it doesn't need to. It can be a thin plate, with just the right geometry so that it is loaded by weight, and stiff enough to "rebound" in a kind of slingshot action.

That's what the Nike shoe purports to do. One journalist who has special access to the project wrote about his experience of the shoes. He said that standing in them felt unstable, and it was comparatively easier to run. Running in them, he reported, made him feel like he was being pushed onto his toes, that he was running downhill.

That's exactly what journalists wrote about Pistorius's carbon fibre blades back in 2012 when they got to wear specially designed versions, and that's no coincidence. The elite athletes who have worn them (sponsored by Nike, remember) report that they have no muscle pain after running, which suggests the shoes unload the muscles, exactly as a spring would do.

Are they legal? That's the big question. My opinion is that they should not be. I don't think any device added to the shoe, acting as a spring, or providing energy return, should be legal. The cushioning material (not added) also contributes to energy return, and should be regulated to prevent absurd advances in performances due exclusively to technology.

The current regulation says that the shoe "must not be constructed so as to give an athlete any unfair additional assistance, including by the incorporation of any technology which will give the wearer any unfair advantage".

Curved carbon fibre plates that add to energy recoil, in my opinion, contravene both clauses. They provide additional assistance, and they do so by incorporating a curved carbon fibre plate.

Where the argument will happen is the definition of "unfair", a loophole big enough for a lawyer to run through. Until then, we count down to May, when the attempt is due to take place.