Have you ever had a long run that you had to do over the weekend and you weren't sure how it was going to? You tepidly go into it thinking "Boy, I hope I can get that 12-14 miler in…", but you have enough experience to know it might be a struggle? But within the first hour of your run, you realize "Hey, this might be my day..." and end up doing more than you planned?
I had such a day last Saturday. I had a 14 miler planned, but with work, being out the night before at a Fantasy Baseball Draft, I didn't know what to expect. But I followed my pre-long run breakfast, drinks, and morning constitutional ritual hoping that it would be enough to get me through. But, as I described above, within the first hour, I was feeling like Blue Steel. I felt like Forrest Gump, like I could run forever.
But from years' experience, I knew I could harm myself from over-doing it. As I've probably mentioned a million times before, patience is one of those skills you have to learn in running or the probability of injury spikes up. So at mile 9, one and a half hours into my long run, I started to work with the rational side of my brain to decide, just how much farer I should go beyond the 14 miles planned. I knew I could go double the distance I had at that point. I was averaging a 10 minute mile with the 30 second walking breaks I was talking to re-fuel. A quick calculation told me that was 3 hours which would give me 18 miles. The longest long run I had up until that one was 12-13 miles at a little over 2 hours. So I rationalized that I would do something less than the 18 miles with the last half mile walking. 17 seemed safe based on that since jumping from 13 to 16.5 is another 35 minutes of running, not an earth shaking difference but not an easy slide either. So I followed my gut and everything worked. Felt like I could've done more but at the same time didn't want to blow the training to that point by over doing it.
That's the hard thing with long runs, you never know what you're going to get. But I can tell you one thing I did at the end of the run. Wrote down everything I had done that morning, the day before, two days before. As I mentioned before, keeping a running diary is important for making those small advancements in your running program. We each have our own formula that works for us. Sure, you can get advice on the big things that you should do (or shouldn't do) the day before running a Half Marathon or Full Marathon. Yet it is the little things that you do, that are unique to you that will help you perform at the top of your game. PowerBar or toast? Coffee or Coke? How much water the day before? Stretches or no stretches before you go out the door? GU every 45 minutes, 30 minutes, or forget the GU, use Gatorade instead of water?
We are all an experiment of one. What works for you, doesn't necessarily work for everyone. But once you find that formula, use it until you have a bad run and tweak it until it starts working again.