Pace is Negotiable. Distance is Not.
When training for a marathon, some long runs go exactly according to plan. (We love those). Some don't. How you handle the ones that don't can have a big impact on how you perform on race day. If you have a sub-par day, there are three ways to handle things: 1 - Go home.
2 - Hold onto your goal pace for as long as possible, but cut the run short.
3 - Go slower than your originally intended pace, but finish the distance.
Option #1 should be exercised if you're sick, injured, or otherwise undermining your long term efforts by continuing to run. It sucks, but fighting it usually just slows your recovery.
But if there's no injury or illness and you're just having a lousy day, you're faced with the choice of hanging on for as long as possible at your goal pace, or slowing the hell down and shuffling through the miles. Far more often than not when an athlete reports back to me that they improvised and changed the workout on their own, they opt to shorten the workout. And far more often than not, I tell them that's the wrong approach. Here's why.
As I mentioned in yesterday's post, my main concern with the long run is "time on your feet". Sure, I'd prefer that it's at the prescribed pace, but for marathoners, there's value even if it's slower. Conceptually it makes sense. On race day if you plan to run a 3:10 marathon and you set out at 7:15/mile but you're a little off your game and come in at 3:20, so be it. You may not get your BQ, but you still get your space blanket and your name in the list of finishers. On the other hand, if you hold your 7:15's until you can't and then walk off the course at mile 20, you'd better hope you have a Metro Card with you.
This also speaks to why I'm always talking about listening to your body and its cues, rather than "tuning out" and distracting yourself. While I obviously hope that you can maintain your pace for the full distance, if you're going to slow down, I'd much rather you make a subtle adjustment early, rather than a drastic (but necessary) one later. When a runner tells me "I was cruising along and then out of nowhere I had to walk", I usually respond with "nonsense". In all likelihood, your body was trying to tell you something for a while, and if you had backed off sooner, you wouldn't have had to back off so drastically. Pay attention during your training runs and check in with what your body is telling you.
And if you have a subpar day, make sure to learn from it. Once or twice can be written off as an anomaly. But if it's happening often, it's probably an indicator that your marathon goal pace is too aggressive or that you're pushing too much on your easy days and not fully recovering for your quality runs.