I normally run 5km at a decent enough pace (4.30km) with no issues. I've started training for a half marathon - but about 10km in, I started getting really bad pain in my left foot.

I stopped running at about 15km and returned home to find a large blister on my foot. I'm sort of flat footed so this could be related.

Does anybody know what might be causing this and how to remedy it?

Photo attached:

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  • 2
    When you say "10km in", is that farther than you normally run? If so, how much further? (And just as an fyi, I'd regard that as mid-arch, not behind the ball. Mid arch is most likely due to increased friction from either shoes that are breaking down, more sweat causing sock wrinkles, something like that. Ball of foot area would be much closer to the big toe, and could suggest gait differences as you get more tired.) – JohnP Aug 1 '18 at 14:36
  • Oh okay, I wasn't sure about the anatomy / naming. Normally I would run 5km so 10km would be double for me. – TomSelleck Aug 1 '18 at 16:36
  • I would also look at a training plan, such as this one: halhigdon.com/training-programs/half-marathon-training/… – JohnP Aug 1 '18 at 16:53
  • Did you figure out what the cause was and how to fix it? I've just had the exact same thing happen. I also normally run 5km at 4:30/km odd pace. I went on a 12km run just now and after 10km I felt pain in the spot your blister was (I thought it might've just been a pebble in my shoe). I came home to a blister the same size as yours in the exact same spot and I'm also fairly flat footed. – AK97 May 24 '20 at 6:43
  • @AK97 Pretty sure getting good shoes helped me. I picked up these which have very good arch support and haven't had any trouble since: brooksrunning.com/en_ie/mens-running-shoes-ravenna-10/… – TomSelleck May 24 '20 at 19:48

According to your comments, you normally run a 5k, and you doubled that. I would caution you against suddenly increasing your mileage when running, as it is easy to get overuse injuries related to the sudden jump. I would also (if you don't already) track the mileage use on your shoes, as most shoes have a life of 3-600 total miles before they should be replaced (YMMV, depending on height, weight, gait, etc).

While I can't 100% say these are the reasons, there are a couple of reasons this might have happened (I put what I thought were the two most likely first):

  • Lacing: As you run, your feet will swell. If you tend to lace tight, then as your feet get bigger you put more pressure on areas that may not be used to it (Especially with a big mileage jump).
  • Sweat: As you run, your feet sweat. On a shorter run, this might not be a problem. On a longer run, it may cause your socks to bunch up in different ways, or just become wetter than normal. This can create a new pressure point, which in turn causes the blister.
  • Ill fitting shoes: Similar to above. There are some uppers (the part above the sole) that are fine for short runs, but chafe/rub on longer runs. This can be due to seams in the material, lacing causing point stress, and so on.
  • Shoes breaking down: As your shoes wear out, the sole may start collapsing in new spots, creating pressure areas. Again, might not be a problem on shorter runs, can be a problem on longer runs.
  • Fatigue: As you tire, your gait can change. You may land differently as you get tired, which in turn creates that pressure spot and so on.

Things you can do:

Check your shoe fit, and track your mileage. While a shoe may look fine, every shoe has a shelf life for mileage. Check your socks, you may need a different fit or thickness to adapt for longer runs. You can try some bodyglide to ease the rubbing. (I never had much luck with that option). Pay attention to lacing pattern, and how tight you make everything. (You may also need a 1/2 size bigger shoe as you get higher and higher in mileage to accommodate foot swell).

If you do all those things, and after ramping up your mileage you still get the blisters, then you may need a pair of outside eyes to assess to see if there is something funky going on.


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