Is carbon the new gold? The running slipper we've all been waiting for

Running shoes are ever-changing and advancing - in style, materials, function and technology. Carbon-plated shoes are the latest development and have been portrayed as the golden running slipper we've all been waiting for...but are they?

An evolving project

Contrary to popular belief, carbon-plated shoes are not a new idea but have been in the making for around 40 years, with Adidas experimenting with the concept in the late 1980s. In the early 2000s, Canadian professor of biomechanics, Benno Nigg, showed that increasing the midsole bending stiffness of the shoe increased static jump height by approximately 1.7 cm. This improved plyometric function builds on previous performance-enhancing shoe modifications such as decreased shoe weight, less air resistance and improved propulsive force.

There is no question that the results being posted by professional athletes wearing these "golden shoes" are impressive at all distances, from 200 m to 100 km. Without an understanding of how the shoe's technology influences the athlete, there may be widespread calls for more extensive drug testing!

Discussion has been robust in the media and scientific literature alike. While the debate seems to focus on the carbon plate being the magic ingredient, notable commentators such as Nigg and Australian sports podiatrist, researcher and shoe designer, Simon Bartold, say that it's more than just the plate.

Carbon-fibre protagonist Wouter Hoogkamer initially showed a reduction of 4% in the metabolic cost of running when athletes wore the Nike Vaporfly. In a 2019 publication, he attributed this to:

• Superior energy storage in the midsole foam
• The clever lever effects of the carbon-fibre plate on ankle joint mechanics
• The stiffening effects of the plate on the big toe.

In a 2021 update and review article, his research group indicated that performance might actually vary from -3% to +3%, and that how the carbon-fibre plate interacted with other features (such as foam and midsole geometry, shoe size, body mass and strike pattern) was equally important.

Leveraging the effects of carbon fibre

So, how exactly do these magic shoes transform running?

All the plate is claimed to do is help maintain the shape of the very thick stack of soft rubber under the foot. In reality, the function of the shoe is the sum of all its parts.

The parts are a composition of vibration-absorbing, energy-returning midsole material coupled with a rocker-bottom-shaped geometry. This shape changes the direction of toe-off. When combined with the rigid carbon plate, it creates a lever action that increases the stride length of the person running. The plate indeed assists, but only when it is rigid enough to be considered a lever and not a spring. The difference between the functions of a spring and a lever is key. A spring by definition is a device that is deformed by a force and returns to the same shape. A lever will not deform but relies on the principles of a fulcrum (axis): resistance and effort.

The foot at toe-off uses the big-toe joint as the fulcrum. The body weight is the resistance and sits between the fulcrum and the effort, which comes from the shortening calf muscle. In addition, this rigid lever (carbon plate) needs a non-complaint or rigid upper and firm lacing in the shoe to assist forcing the energy of the toe-off into the plate. It cannot work effectively on its own.

Injury intervention from the feet up

The meta-rocker shape can definitely assist in the management of certain injuries, specifically injuries around the big-toe joint, ankle, Achilles and calf. The shoe shape helps reduce work (movement) at these sites, which is part of its magic. But, we caution, it is best to discuss these problems with a sports podiatrist, as effective intervention should not be seen as an over-the-counter quick fix. Usually, it would include a combination of shoe selection, orthotics and rehabilitation.

It is also too early in the evolution of these shoes to know whether they may also contribute to causing injury or what the injury profiles may be, so caution is key here if you are injury-prone or just starting out.

A shoe for all surfaces?

Carbon plates in trail shoes? Most trail shoes already have rock stop plates for protection, but these are not as rigid as carbon plates.

Running on flatter jeep track and smoother single track should not present a problem; however, they should be used with caution on technical trails. If your foot placement is off on a small point, the lever action of the plate could cause or exacerbate injury to the foot or ankle.

That said, there are some shoes with carbon plates and others with graphene-infused plates which don't function the same way as a carbon plate. Look out for innovative trail shoes from the likes of Hoka One One, Inov8, North Face and Salomon.

Where do we see faults or potential problems?

These shoes have been used in races that are mostly on flatter courses; we haven't seen what will happen on a hilly course like Two Oceans or Comrades. Some athlete feedback suggests that runners work harder running up hills while wearing carbon-fibre.

An unfair advantage...

This was the subject of widespread debate on carbon plates in shoes a couple of years ago, prompting the World Athletics (IAAF) to stipulate clear regulations for shoes to be worn in competitive events. In essence, these are:

1. The stack height must not exceed 40 mm (for road shoes) and 20 mm (for track and field).
2. There may only be one plate inserted.
3. The shoes must be the same as commercially available shoes and they must be on the market three months prior to being used in a race; no 'prototype shoe' may be worn to race.

Will carbon plate shoes work if you don't have a cadence of about 180 and a stride length more than 1.5 meters, like most pros? There may be limited benefit from the shape and material of the midsole, but remember that energy doesn't come for free: if you don't put energy into the shoe, you won't get anything back. If your running style has a low cadence with a short stride length, then a carbon-plated shoe will not alter this much. Unfortunately, a slow plodder is unlikely to now crack a sub-two-hour marathon...

Will these golden slippers at least give you a personal best? There may be a glimmer of hope here with some possibility! But only if you do the strength work required to strengthen your core, hips, knees and calves. Add in some speed work to increase your cadence and stride length, use different shoes for training - with some training reserved for the racing shoes - and you could see improvements.

....at what cost?

Carbon-fibres are more expensive than regular running shoes. The newer technology seen in the midsole materials, and the carbon plates, do add to the price. You can expect to pay between R3 500 to R5 500 for a pair. Remember, they are race shoes! If you use them for training it may become a prohibitively expensive habit.

A golden age

All in all, running is entering an exciting new technological era. As this technology evolves and more runners invest in carbon-fibre shoes, we'll see how "golden" this slipper really is as we measure its influence on the average runner's performance and injury profiles.