It's a lovely run, largely flat and past many of the capital's most famous landmarks. There's a wonderful atmosphere to it as well - something rather inspiring about being part of an event with 12,000 eager runners, many of them sporting the vest of the charity they're doing it for.
As you can see from my selfie, it starts (and ends) on The Mall outside Buckingham Palace, which makes it feel like a proper race. The sun's shining (usually), there are bands playing and spectators lining the course and cheering you on - you do feel quite special while you're running it. The weather didn't entirely play ball this year, however - from about an hour before the start, you could feel the humidity climbing and it was pretty clear that it was going to be a bit tougher than normal.
Regular readers of this blog (both of you) will know that my training has not been exactly inspiring going into this race. I even had to pull out of a parkrun halfway through a couple of days before. Something isn't quite right - there's a lack of stamina that's bothering me, so my aim for the day was to get round, pace myself carefully, and not worry too much about how cripplingly slow I was actually travelling.
It didn't quite go to plan. For the first couple of kilometres, I found myself running quite comfortably. Quite, well, fast even. On schedule for a personal best. I made my first mistake, however, at the water station about 3.5km in. Took a bottle, a quick sip and then poured the rest of the contents over my head to try to cool down.
I've done this before. In moderation it's a good tactic. Using the whole bottle, however, is not. Immediately, your (now sopping wet) running vest sticks to you like over-enthusiastic clingfilm, making you hot and clammy and damp at the same time. I spent the next kilometre fruitlessly trying to peel the vest off my chest, which I can tell you does nothing for your running style.
Still, by halfway, I was still going pretty well (about 5 mins 12 secs per km, for anyone interested) when it all started to go wrong. I'd just rounded the Bank of England and was heading back towards St Paul's Cathedral when the heat and the humidity finally caught up with me, and my legs started to feel heavy and cramped.
I could almost feel the speed leaking out of me. It really did feel like running through treacle, just a battle to keep on going. I struggled on for a little, tried to get my mind to force my legs to keep going, but couldn't do it. I had to stop and walk for 100 metres or so to try to recover my energy.
From then, it was a bit of a disaster - stop-start, stop-start, getting slower and slower as a result. Once you've taken a break, I've found, it's really hard to get back into the right mental state - and I certainly didn't manage it this time.
The picture here doesn't quite do justice to how terrible I was feeling at the end. Perhaps I should have taken one of me a few seconds later, hunched over the crash barrier, trying not to crumple into a sodden little heap. I was so exhausted I even managed to knock back one of those vile Weetabix protein drinks they give you in your goodie bag along with your medal once you've finished.
My time? Probably best not to ask. Suffice it to say it wasn't a personal best or anything close to it, so it's probably a good thing I'd decided not to worry about that. It was under an hour and let's leave it at that. The second-slowest I've ever run this particular course.
I'm more worried about how I couldn't just keep going. It's possible I set off too fast, but even so, this is only 10k. A quarter of the distance I'm setting out to run (slightly less than a quarter in fact, but who's going to quibble over a couple of km). A vast improvement is needed. Soon.
