'Build up slowly' for barefoot runs
Careful readjustment is vital for anyone taking up barefoot running, sports scientists have warned.
An overview of research was presented at the British Science Festival in Newcastle.
Claims that running without footwear might improve technique and result in fewer injuries have led to many runners taking it up.
Dr Mick Wilkinson, from Northumbria University, also claimed that it was best to start off on hard surfaces.
He told a press conference that when he made the transition to barefoot running, he started on soft surfaces and gradually moved to harder ones such as concrete, but that if he could do it again, he would start off on hard concrete.
Dr Wilkinson was one of the first people to run the Great North Run completely barefoot, which he did in 2011. But he believes that those using thin-soled shoes which claim to emulate barefoot running may be missing out on the potential benefits from running without footwear.
Running shoes have got much more hi-tech over the last few decades, but levels of running injuries have not changed over that time. It is thought that this is due to the built-up cushioned heels of modern shoes causing runners to hit the ground heel-first.
Researchers who have investigated people who habitually run barefoot noticed that they land further forward on their feet, in the mid- or fore-foot area. Elite athletes also more often run in this style too.
Dr Wilkinson said he would advise anyone taking up running for the first time to run barefoot, or with very lightweight flat-soled flexible footwear. However, he cautioned against going from conventional running shoes to either thin-soled shoes or barefoot without careful adjustment.
"I'd advise people to think before they decide to change their running style. If you immediately try and change the way you run, that causes problems, and there's some literature to suggest that initial adaptations to try and change your running style can result in other injuries manifesting themselves."
He also suggested that it's the contact with the ground directly that helps a runner change their style, as the friction triggers a reflex drawing the leg away from the impact, and helping the runner to prevent stress injuries.
"Studies in the late 80s suggest there needs to be a sense of friction before the impact avoidance behaviour is triggered. So if you put anything between you and the ground, even if it's only 4mm thick, people tolerate extremely high vertical loads, without doing anything about it," Dr Wilkinson explained.
He described barefoot running as a good tool to change your running style, even if a person doesn't want to throw their running shoes away completely.
"It can be a useful way of helping you to acquire a different running technique. Because if you're taking off your shoe you get that much more feedback, you get that sense of friction which triggers the impact avoidance, and it's very uncomfortable to land on your heel, so you avoid doing that," he said.
"It also forces you to drop your training volume down massively. If you try to continue the miles you're doing barefoot, your feet will fall to pieces. So you have to build up again. You literally can't do too much too soon if you run completely barefoot, your feet won't let you."
Dr Mark Burnley, a senior lecturer in exercise physiology at the University of Kent, told BBC News: "Barefoot running is an interesting phenomenon as it goes in and out of fashion quite regularly.
"[In my opinion] There is simply not enough epidemiological evidence to demonstrate benefit either way, and an analysis of the biomechanical differences suggests that the benefits gained (reduced impact peak) are offset by the negative effects (increased stress on other structures). In short, adopting a barefoot running style is certainly possible, will save you money on shoes, but is not some injury-eliminating/performance-enhancing panacea."
Dr Wilkinson also made it clear that there was little detailed research on injury rates in barefoot running, at performance improvement from changing to barefoot running, or whether the benefits of barefoot running are definitely from changing where on your foot you land, rather than something else to do with taking your shoes off.
Not all experts agree that you need to run completely barefoot to get the benefits though. Stuart Miller, a senior lecturer in biomechanics at the London Sport Institute, Middlesex University, told BBC News: "It appears that even with use of very thin running shoes, people will still transfer to forefoot striking. The difference in rate at which people will transfer when using [barefoot emulating] shoes compared to barefoot is likely to be minimal.
"There just isn't a study with a large enough sample size, or enough studies investigating the matter, to warrant any conclusion on that."
He agreed with Dr Wilkinson's conclusions about gradually transitioning to barefoot running. "Initially, the pain/stiffness can last up to about two weeks, so do take this into account when thinking about your next barefoot run; let your body adapt, and don't try to 'run through it'."
But he is a fan of barefoot running himself, saying: "I think if the progression into barefoot running is gradual and controlled, then I don't know of any negatives associated with it… other than standing in something you don't really want to."