Why My Calves Cramped On a Long Slow Run?

I have a theory why I suffered from calf cramps during my 31-kilometer marathon-preparation long run.

I am forefoot striker. I used to strike with my heels but learned that I could run faster by switching to forefoot running. The transition went rough. My calves often hurt as I tried the new strike. Gradually, I used the forefoot strike more and more during runs. And as I got comfortable with it, I began to use it with my speed workout runs. Later on, the tightness on my calves disappeared and I managed to successfully switch to forefoot running.

Then came my Milo marathon preparation. After several 21-kilometer Sunday runs and three 27-kilometer Sunday long runs, I went up to 31 kilometers. That was on the 8th week of my 15-week marathon training. Pained and exhausted, my training run speed went as slow as 7 minutes per kilometer. I finished the 31 kilometers on an average pace of 6:08 min/km.

Then after that run, my calves tightened and would always cramp after just 1 or 2 kilometers of running. For the next three weeks, I had to rest the cramping calves. I really had no other choice, I was only able to run 2 to 5 kilometers on each training day and they only aggravated the pains on my left and right calves. Rest became mandatory.

The 3-week hiatus proved costly. I finished my second marathon in 5:22 hours and had to walk the last 13 of the entire 42 kilometers.

Why it happened?

My theory is that running with the forefoot strike on a slow pace of 6:00 min/km (and slower) puts a lot of pressure on the calf muscles. I experienced it while trying to learn the strike. I would run slow just to feel how it is to run with my forefoot. It was really painful on the calves. Then as I get more comfortable and faster with it, the pain disappeared. But when I tried the much longer runs where I had to slow down because of fatigue, my calf muscles were again put to a lot of stress.

I am not a doctor or a specialist.. I am just observing how my body suffers from running and what I could to to avoid pains and injuries and improve my running form and techniques. That said, I have the following adjustments to make sure my training does not suffer from the same set of cramping calves:

1. When running long distances, especially during my Sunday long runs, I do try to switch back to heel striking when my pace is dipping and I can't do anything to speed up. In doing so, I am using different sets of foot and calf muscles that leaves my forefoot-running muscles to rest and recover (until  the moment I can run fast again and switch back to forefoot running). 


2. I have a mandatory walk break halfway thru my long distance run. I will buy drinks (I prefer Cobra Energy drink) and carbo-loaded food (pandesal or any bread sold at the bakery). I will then consume the bread and drink the refreshments while walking for a few minutes. Again, I am shifting to other group of muscles and letting my forefoot-running muscles to have their much needed break. 


3. I strengthen my calves once a week by use of weights. I have three strength training sessions each week and one of those sessions focuses on strengthening my leg muscles.

After the Milo marathon incident, I am happy to write that I haven't encountered the same problem anymore. But my theory is still what it is as of now -- just a theory. The jury is still out on whether this theory is right or wrong when I start to train for my third marathon and start to run that 31+ kilometers of Sunday long runs.