feet with sand

This will probably increase your risk of blisters…

I love this academic paper. It’s a great example of a topic that you might not even think to apply evidence. It’s an important one though: how can you avoid blisters when running?

Worthing RM, Percy RL, Joslin JD. Prevention of Friction Blisters in Outdoor Pursuits – A Systematic Review. Wilderness Environ Med 2017;28:139–49.

I really love it when these little niches get addressed and someone actually tries to pull together the evidence. It might seem like a minor topic but those tiny little abrasions can completely destroy your ability to get around your chosen event, whether it is completing an ultra, or just enjoying a simple walk on the hills.

This is systematic review had a stated aim to: determine if sock, antiperspirant, or barrier strategies were effective in the prevention of friction blisters of the foot in wilderness and outdoor pursuits.

First of all. First of all, we can’t go too far without defining a ‘friction blister’. Here’s what the authors offer:

Friction blisters result from pressure and shear forces causing delamination at the level of the stratum spinosum.

And just to really ham up the proper science-y element of this let’s throw in an equation.

Frictional force (Ff) = μ x Fn

And that’s it. In order to prevent blisters you need to reduce the coefficient of friction (μ) or reduce the shear force (Fn). Or, preferably both. What are the options? Here are a few:

  • variable sock material and knits
  • different sock layers/systems
  • lubricants
  • anti-perspirants
  • orthotics

The Results

The authors went through the formal process of a systematic review: agreeing a search strategy and identifying papers which are then systematically assessed for bias and confidence in effect. They found 806 titles in 12 languages from 1950 to 2016. Most of those can be dropped with a quick scan of the title and the abstract giving them just 20 to look at in detail. Another 9 were binned for not being relevant and they ended up with 11 studies.

So, that’s it. For all the work in this area there are only 11 studies that actually offer something meaningful to answer the author’s question.

It’s hard to work out much in the way of meaningful results with these studies.

But the problem is that even four of these studies seemed to have real problems with bias. And the other seven had assorted problems with conflicts of interest, general imprecision, and being part of multiple interventions. It’s hard to work out much in the way of meaningful results with these studies.

The three studies with the lowest risk of bias are worth looking at a little harder. One was a non-blinded randomised controlled trial in Belgian officer cadets during their 6-week basic training. Polyester padded socks performed a lot better than polyester thin inner socks + cotton wool blend outer or standard issue 70% wool socks. They also found an association between overuse injuries and blisters.

A double-blind randomised trial in US Army soldiers after they got them to do a 200 minute treadmill march (ouch, not sure how that got past the ethics committee) tested antiperspirants versus placebo. No differences were found at all.

Another non-blinded controlled trial in endurance athletes tested out prophylactic paper tape application against no treatment during a 155-mile, 7-day race. There was a reduction of 40% in blisters and 81% of the athletes said they would use it again.

Conclusion

No study is perfect, they all come with some flaws. But in a lot of studies the flaws can be a little overwhelming and massively limit how far you can draw conclusions. The problem with the blister studies is that it’s hard to find any that are hugely helpful.

Advice for blisters in a nutshell

My advice currently: find socks that work for you and test them out. There is very weak evidence that a single pair of padded polyester ones are slightly better (but that was in young recruits who presumably spent a lot of time in boots). That probably fits with general advice that synthetic materials are better at wicking sweat – it’s those soggy feet that can get torn apart by frictional forces.

The evidence for taping your feet is a little better. Reading this, I’m definitely going to try it for any longer efforts, especially anything multi-day.

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