The pain comes suddenly, like I’ve been hit by a bullet. Both calves cramp simultaneously, each one curling in onto itself, forming the smallest possible shapes they can. MY legs buckle. I grab at a nearby lamppost to steady myself. I don’t fall, but it’s close. For some reason, I look at my watch. I’ve been running for exactly two hours, thirty one minutes.

I’m eighteen miles into my Saturday run, with just two more left to go. Up until this moment, I had been running incredibly well. In fact, just moments before, I was telling myself what a great run I was having, and maybe I could tack a few extra miles on, maybe even do the entire marathon distance.

In many ways, this was a good run. No, a perfect run. I’d left home at 1pm, the cool September weather perfect for running in. I had my favourite…