Running Cramps During the Marathon

When I run marathons I have this one problem. I always cramp up badly by about mile 20. How can I figure out what to do? Don't know how to fix this. Thanks in advance.

– Ray

Answer by Dom:

Hi Ray,
The marathon is an unforgiving distance. Running cramps, especially in the lower leg, are quite common for marathon runners.

Without knowing much more about you, there are three likely causes:

1. Training – not enough long runs, so your legs haven't been conditioned for the distance
2. Fluid and fuel – electrolyte depletion through sweat
3. Pacing – starting too fast and running out of fuel towards the end

Here's the thing though: the fact that you cramp always by mile 20, like clockwork, is actually a useful clue. It's a classic sign of one specific cause, not all three equally. Let me break the three down properly, because fatigue-cramps and electrolyte-cramps are different problems with different fixes.

Training: Fatigue-Cramps

Fatigue-cramps come from your muscles simply being overloaded, i.e. asked to do more than they're conditioned for. This is the classic mile-20-to-22 story, and it's what I suspect is going on for you.

You can't really race a marathon until you can do 20-milers easily in training. If your longest runs regularly stop short of that, or if you only get there once or twice and it feels brutal each time, your legs simply haven't had the repeated exposure they need to hold up for the full distance. The fix is more long runs, done consistently, not just one heroic 20-miler a few weeks out.

Starting too fast plays into this too. If you go out quicker than your legs are conditioned to sustain, you'll burn through your muscles' capacity earlier, and the cramp shows up at roughly the same point each time because that's when the accumulated damage tips over. You can read more on this on the marathon pacing page. Given you cramp at the same spot every single race, I'd put my money on insufficient 20-milers combined with going off too hard, over anything else on this list.

Fluid and Fuel: Electrolyte-Cramps

The other main cause is different: electrolyte-cramps come from mineral depletion through sweat, not muscle fatigue. You lose sodium and other electrolytes as you sweat, and if you're not replacing them, cramping can follow, independent of how well-trained your legs are.

The fix here isn't more long runs, it's sodium and electrolyte intake during the race itself, alongside your normal fluid and fuel plan. See this page on running with calf cramps for more on managing this.

It's worth testing your own sweat rate and salt loss in training (a salty face or crusty singlet after a long run is a fair sign you're a heavier sweater) so you know whether this is likely a contributing factor for you specifically.

Pacing

Starting off too fast ties both causes together. Go out faster than your fitness supports, and you'll fatigue your legs earlier and burn through fuel and fluid faster too, so pacing discipline helps with both fatigue-cramps and electrolyte-cramps. Even splits, or a slightly negative split, protect you against both.

I am guessing a lot of your problem comes down to insufficient long-run training and going out too hard early. But for us "mere mortals", the 20-22 mile mark is also simply the point where the body starts to heavily react to the accumulated stress, however well-prepared you are.

There's a well-worn saying among marathoners that the stretch between 23 and 26.2 miles is "no man's land" — the point where you're relying on character and will as much as fitness to hold your speed.

So, although not much of a consolation, at least you're in good company if you're suffering from problems at the end of a marathon. Build up your 20-milers, hold your pace back early, and dial in your electrolyte intake, and you should see this improve.

Hope this helps.

Kind regards,
Dom

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