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Are carbon shoes making us injured?

Runner's World UK logo Runner's World UK 30/11/2022 Lily Canter

Super shoes are the footwear of choice for elite athletes around the globe, but since spiralling in popularity among amateur runners, some have have started to question whether carbon shoes cause injury.

To date there has been no research published examining the correlation between carbon shoes and injury, due to the shoes being so new and it not being in the industry's best interest to find out. However, sports scientists do have some indication of how, why and where injury is likely to occur.

Injury research is extremely hard to conduct, says Hannah Rice, associate professor in biomechanics at the Norwegian School of Sports Sciences, because it involves hundreds of runners over an extended period of time which is costly.

'There has not been a shoe found that reduces injury because everyone runs differently. It would need to be an individualised shoe, which would need so much funding to do the research and create the shoe,' explains Rice.

Part of the problem is that the vast majority of research is conducted on elite, rather than recreational, runners, who train and run very differently, says Kim Herbert-Losier, researcher in sports biomechanics at The University of Waikato.

But there is a growing base of anecdotal evidence that carbon shoes cause recreational runners pain and injury that does not occur in traditional road shoes.

Instability issues

Herbert-Losier, who has co-authored papers on the kinematics of super, minimalist and habitual shoes and the running economy of super shoes, has conducted qualitative research on injury and carbon shoes but her data has not been published yet.

The study involved testing people whilst they ran on the road, a more natural experience than training on a treadmill in a laboratory.

'Some people didn't like running in carbon shoes particularly when they got to the corners because they felt quite unstable which makes sense because you are running on a higher heel. The participants were afraid that they were going to twist their ankles. Some of them said they wouldn't buy the shoes because they felt too unstable,' says Herbert-Losier.

And when speaking to elite athletes she has also found there are similar concerns.

'I know of an elite triathlete that decided not to wear them on a particular race that had a lot of bends because they were concerned about twisting their ankle. And I was recently talking to a triathlete at the elite level, who raced in them in and then had hip issues for three weeks after racing.'

Biomechanical adaptations

Running in carbon shoes changes your biomechanics, as they activate different muscle groups © Boston Globe / Getty Running in carbon shoes changes your biomechanics, as they activate different muscle groups

Running in a carbon plated shoe with a high stack and spring-like foam will cause biomechanical adaptations which sports scientists speculate can lead to muscle ache and potential injury.

'I think the big thing if we're looking at recreational runners is it's going to change your own biomechanics considerably. It's going to be activating different muscle groups and exposing you to different forces and laws that your body wasn't previously used to,' says Liam Walton, sports scientist and validation manager at INCUS Performance.

So while runners may not get injured, their susceptibility to DOMS (delayed onset muscle soreness) may increase when switching to carbon shoes.

'DOMS indicates you are using muscles in a different way than before,' adds Rice.

Getting habitualised to a shoe and switching over gradually is the key to avoiding unwanted pain or injury, so the muscles are able to adapt and become stronger.

Herbert-Losier explains how the launch of the minimalist shoe made famous in the book Born to Run saw many runners getting injuries in their ankles, calves and achilles because their feet were not used to running without support structures. But with gradual integration of the shoe, runners' feet can become stronger as the bones gradually adapt.

'The benefit of the Nike shoe (Nike Zoom Vaporfly 4% Flyknit) is that is tends to be closer to a traditional shoe. The key is, if you want to run in these shoes, integrate them sensibly, and progressively, within your training program,' says Herbert-Loiser.

Another change is that because the shoes are more efficient, wearers are likely to run faster which has an impact on biomechanics and muscle use, says Rice.

Herbert-Losier agrees: 'If your body is used to running in a certain way, with a certain shoe, then your tissues aren't adapted to that kind of (faster) workload.'

Injury distribution

Although there is no tangible data on carbon shoes and injury, sports scientists do have some indication of where injury is likely to occur.

'The shoes have an impact in terms of where the load is distributed,' explains Herbert-Losier.

'In traditional shoes you tend to get more knee injuries, or hip injury or lower back injuries, which are more proximal in nature. In minimalist shoes they tend to be more distal, your feet, ankles, calf and lower leg. If we speculate on the injury distribution that we might see in super shoes, the pattern would be more comparable to traditional shoes because of the higher heel and the cushioning. You'll probably keep seeing knee, hip and back injuries. And we might throw in angle sprains because of the instability,' she adds.

Muscle atrophy

However, the impact-absorbing properties of the foam in carbon shoes, which works to reduce the amount of force in parts of the body, could also reduce injury risk, says Walton.

The prominent research on carbon shoes, conducted by Wouter Hoogkamer and published in Sports Medicine, found less ankle extensor movement in the Nike super shoe prototype and reduced work in the metatarsophalangeal (MTP) joint in the foot.

But sports scientists speculate that decreasing the work output of the lower leg muscles could actually lead to atrophy of those muscle groups. This could lead to injury and negate the effects of the shoe.

'It's two sides of a coin. By using the ankle less and having less flex at the ankle, there's less chance of injury, but in the longer term, if you're not using those muscles as much, are you going to have an under-use injury?' says Walton.

Herbert-Losier also suspects that the lower-leg muscles could weaken if runners come dependent on carbon shoes.

'If you look at the literature, one of the key things that does come out is that it does lower the load at the ankle, at the calf muscles, at the achilles and potentially the foot as well. And I would be concerned that actually you might go towards a disuse of those structures,' she says.

Psychological factors

A look at the start line of any marathon reveals the growing popularity of carbon shoes © Anadolu Agency A look at the start line of any marathon reveals the growing popularity of carbon shoes

And then there are the psychological factors that come into play when lacing up a pair of carbons.

If runners believe the shoes will make them faster and buying a pair motivates them to set new PBs, they could increase their running speed, intensity and duration, which in turn escalates the risk of injury.

'Unaccustomed activities is one of the greatest risk of running injury. Too much, too soon. And if you buy them to train for a marathon, you are running longer and therefore increasing your chance of injury. But runners often trade off performance for injury,' says Rice.

Something which Walton agrees that runners have a habit of doing.

'I've spoken to coaches and athletes who have had injuries from lower back pain, to plantar fasciitis, to achilles troubles, because of the carbons. But that psychological element if you line up on the start line of a race, and don't have carbons on and everyone else does, you are going to be thinking, I'm already at a disadvantage,' he says.

Happy medium

Carbon shoes may not be for everyone but if you do want to integrate them into your running schedule, then don't just save them for race day.

'You need to get use to them and allow your body to have time to adjust,' says Rice.

A 'happy medium' is to use the shoes for speed work and tempo sessions and mix them with your usual shoes, so you are neither reliant on them or not adapted to them, says Herbert-Losier.

And setting a target before getting carbons is also a good tactic, says Walton.

'If you want to do a sub 20-minute 5K, or even a sub 25-minute 5K, set that as your target. Once you've achieved that target, think about those extra bits. Work on fitness, technique, strength. And once all of that is achieved, get some carbon shoes. Gym, nutrition, lifestyle are your 96 per cent, so focus on them first and then the shoe is your extra four per cent.'

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