Yesterday was a 20 miler.  Great morning for it.  Cool and clear with a little breeze. Felt great, ran great, until mile 17 and then things fell apart.  Specifically, my last 3 miles were 12:46, 13:47, 12:51 after staying pretty much around 11:30 the whole way. Not exactly the boost heading into Chicago that I was hoping for.

Here's the workout

I'm hoping if I describe what I was feeling, one of you may be able to diagnose what was going on:

• Could not get my heart rate to stay under 170. I was having to take walk breaks, and as soon as I started back up I was back up near 170.
• My legs hurt.  Not in the joints, more like all over.  Even if I ignored the HR, the legs just wouldn't cooperate.
• Even on some pretty steep downhills, I couldn't generate any pace nor could I recover HR.

I'm figuring either a)I was dehydrated; b)I was out of fuel and either "bonked" or "hit the wall" (not sure what that would feel like); c)I ran too fast for a relatively hilly course and just exceeded my conditioning; d)I'm overtraining and 43 miles for the week (starting with a 10K race) was more I could handle; e)it was just a bad day.

Some details:

• I felt good at 16 so I picked the pace up to 11:00.  This is when my HR went over 170 and stayed.  Looking at my chart I was actually exerting more effort at 15 &16 then I realized so maybe I wasn't feeling as good as I thought.
• Course was predominantly downhill 11-16, slight uphill for 17 and then significantly uphill for 18 and 19.
• While the course was cool at the start, once the sun got high, things did get pretty warm.
• Due to a brain lock and some course confusion, I'd had .5 liter of water between 8.5 and 16. Several cups of gatorade at 16 and then a .5L for the next four miles (it was gone by 19). Also, again because of course confusion, I'd had only 2 GUs in the first 16 miles.

I'd appreciate any insight y'all might have into what might have been going on.  I've got another 20 on the schedule in 2 weeks, but the marathon is 2 weeks after that, so I've got to make some decisions on whether that's a good idea or not.

Thanks in advance.

I no veteran but I've been there, several times. 

But keep and eye on your HR this week during your runs. If it's out of whack, slow down, let someone know, and maybe call it a day - a skipped mid week run will not hurt your endurance at this point. IMO.  

The good news is you got the 20 miler under your belt and your body will respond accordingly. Your cut back week and next 20 miler will most likely be easier. Just take it easy heading into mile 16 - 20. 

As Russ once said, and it couldn't be more true, having these kinds of runs is kind of a right of passage. Welcome our newest member, Brian, to the long run death march club. (Unless you're already a member, in which case, welcome back). 

Thanks for the feedback, all.  I'm going to look at this as a fortunate wake-up call: can't slack on pre-run prep (carb loading, pre-hydration, planning), can't slack on hydration and fueling during the run, and can't lose discipline on pace management.  Better to learn these lessons this week rather than on race day. 

Thanks again for the advice and for taking the time to look at what I'd been doing.