I'm registered for my second ever marathon, doing Portland again this October. My first attempt was two years ago; while I finished it - and that's certainly an accomplishment in itself to be proud of - it did not go well. After so many weeks of high (relatively speaking) mileage, it was far too easy to go out too fast; I beat my then-half PR by the midway point, and totally bonked super early around 16, leading to a really slow and miserable final 10 miles.
There were a few problems that contributed to finishing an hour over even my slowest time goal:
1. Delusional time goal.
2. Poorly designed training plan.
3. Lack of commitment to training plan.
Let's start with the time goal. Though I didn't have a time goal per se - obviously your first time the real goal is just to finish - you nonetheless need to have some expectation of what is reasonable, in order to properly pace yourself.
There are tons of calculators and charts to figure out what pace you can sustain for a given pace, based on your pace at a different distance. What you're truly capable of is going to differ by person, of course (slow twitch versus fast twitch muscle fibers, etc.), even with good training; but the general trend is going to be similar. And that trend isn't linear - you can't just double your 5k time for a 10k; if you're giving you best effort for a shorter distance, you shouldn't be able to hold it for a longer distance.
For the marathon, I've heard as a generality to double your half marathon time, plus 10 to 20 minutes. For slower runners, probably on the longer side of the add (after all 10 minutes is a smaller percentage of your total pace, the slower you are). When I started marathon training, my half PR was 2:58:48. I thought I should pace the marathon for a goal for 5:30, maybe 5:00 if the training went really well.
I'll give you a second to do the math there... in other words, I thought I'd go ahead and run 26 miles at 1 to 2 minutes faster per mile than I was currently capable of running 13 miles. I did bump down my half PR to 2:48:42 during marathon training, but even that put 5:30 as a waaaay stretch goal (i.e., basically maintain the same pace).
Because of the higher mileage and high long runs, for the race itself, that pace didn't actually feel that hard - I actually set a new unofficial PR by the midway point of 2:42! - but, shockingly enough, I couldn't hold that for the entire time, and ended up walking huge chunks of the last 10 miles. Had I instead started on pace for, say, a 6:00 marathon, I might have been able to keep it up.
Now, I was able to improve my pace at shorter distances because of the demands of marathon training. But that plan, in terms of truly preparing me for a great marathon experience? Wasn't so great.
I put together a plan myself (because really, who knows better how to train for a marathon than someone who's never done so before?), based on some internet sources. I mostly figured that what mattered was (1) total weekly distance, (2) long run distance, and (3) some inclusion of speedwork. Which, yes, to some extent. In order to just physically be able to finish at all, that's enough. But not enough to make sure you really know how to keep on your goal pace (or know what your goal pace should be).
But even with two 20-milers, my total weekly mileage was only planned to peak at 40 - that's not really that much compared to running 26.2 at once! There are really a lot of nuances, based on how you body reacts to runs, how you much time you need to recover, whether you can handle cumulative fatigue, that ought to go into a training plan, that I didn't even know I needed to consider.
I also didn't stick close enough to the plan, such as it even was. Not that you have to 100% hit every single workout as prescribed, but you have to be reasonably close. I did hit two 20-milers, but they were slow and miserable, because I didn't built up to them properly after falling short on earlier log runs. I frequently fell short on both long run distance and total distance, peaking at only 38 miles for a week.
I talked about this a bit in this post at the time. A long-ish road trip and other summer goings-on made it so easy to make excuses of ways to spend time other than running. And though I didn't burn out on running altogether, this kind of training made running hard! I knew I had to put work in in order to succeed at the marathon, but I don't think I fully realized how much work it took, until I proved that I hadn't put in that work.
This time, I hope to avoid these issues, and let whatever it is that will go wrong over 26.2 mile at least not be something of my own doing! I've decided to do the Hansons training plan, and will talk about that in another post, hopefully up tomorrow.