How I look after my feet will likely decide whether I finish Marathon des Sables or not. The organisers say that, after dehydration, foot problems are the main reason that people fail to complete the race. My feet could swell by up to three sizes in the desert heat, and come the latter stages of the race, they might also be heavily bandaged. Well-fitting shoes will be crucial to avoiding blisters for as long as possible. I’ll talk about shoe-fitting in a future post as I experiment with minimal and maximal cushioned trainers.
After shoe-fitting, sock choice is the next biggest factor in blister prevention. Ultra runner Jim Benike speaks from experience of the Marathon des Sables when he says, in John Vonhof’s excellent book ‘Fixing your feet’, that, in addition to sand, smaller grit and dust get into every nook and cranny of your shoes, socks and feet. He wore standard runners’ double-layer socks for MdS and found that layers of grit and dust got trapped between the sock layers turning his socks into sandpaper after day two, and no amount of handwashing could get rid of it. Socks should be moisture-wicking as well. I know this to my cost.
There is a well known maxim in running that you don’t change anything on race-day, so when I wore through my favourite running socks a week before the Edinburgh Marathon this year, I bought some new socks with no chance to run them in before the big day. There was some small print on the sock packaging that said that I needed to wash them first, but I ignored that. When it came to the marathon, I remember turning to Nic, who was running with me, at mile 12 complaining that something odd was going on in my trainers. My new double-layer socks were not effectively wicking moisture. My franken-feet looked pretty grim immediately after (see the picture above), and I ended up losing eight of my toenails. Mine are the feet on the left, while Nic’s beautifully pedicured feet are on the right.
After shoes and socks, it’s all about shear. Again, according to John Vonhof, apparently a combination of the repetitive loading vertical to the skin, and the side-to-side load, parallel to the skin causes a shearing action that causes micro-tears in the layers of skin beneath the surface, which fill with fluid and possibly blood. Allowing socks to slide over the skin, counter-intuitively, reduces the likelihood of blisters as it reduces shear. This can be achieved with vaseline, and with low-friction tape. One can imagine how grippy tape could cause the skin to grip and repeatedly shear over the underlying bones causing blisters. So it’s not trainers or socks rubbing against skin that causes blisters, but rather the skin grips your socks and your socks grip your shoes and then every step causes your bones to move against your skin which cannot move, and so creates those shearing forces.
These last three weeks I have increased my mileage significantly with two 45 mile weeks and a 48 mile week. This increased load is helping to condition my feet to endure more shear before the blisters kick in. I’ve also been running on beautiful empty Northumberland beaches to get my first experience of running on sand.
I learned two lessons from my beach-running experience: I’m considerably slower on sand, and I have used lots of muscles that I never knew existed, judging by the Delayed Onset Muscle Soreness (DOMS) I’ve experienced since. Oh, and the headwinds!