Raise your hand if you're in the midst of marathon training. Raise your hand if you had a recent 14, 15, or 16-mile run that freaked you out? Was it a tough one? Were you freaking out, thinking, "That just about killed me! How am I going to run 26.2 miles?"
You're not alone. I call it the 15-mile Freakout!
Not sure what it is about the 15-mile mark, but it's a common mileage for a mini-meltdown to occur. You're probably about a month into your training and your body is still acclimating—physically and mentally. You're putting a lot of demands on your body and it takes about 4 to 6 weeks for the body to level out and really start to feel stronger than when you started. Particularly if you're a first time marathoner, mile 15 is typically quite a milestone. It's the bridge from that familiar 10-miler to the new frontier of the yet-to-achieve 20-miler.
The cause of that hard 15-miler can the result of the accumulation effect, just all those weeks of more mileage than you're used to coming to a peak at the 15-mile mark. You're body is fatigued and telling you so. After a really hard run like this, it's fine to modify your training to allow for some extra recovery time. Typically after a long run, you'll have a complete day of rest in your plan. Definitely take that, but also take a second day of rest, if needed. Or, if the next run after your post long-run rest day is a speed workout, make it an easy short recovery run. Allow the legs time to recover.
Often another cause of the 15-mile freakout run is lack of proper fueling or hydration. Up to this point, doing what you normally do for your normal 8 to 10 milers has probably worked fine, but now that you're running longer and your body is needing more fuel and hydration support. This run is often the wake-up call letting you know the one piece of toast and cup of coffe before your long run and maybe a sip of Gatorade or water on the run just ain't gonna hack it. Your 4 months of training is not just for training your body. It's also time for you to figure out how to best fuel and hydrate your body. These training long runs are the time to figure out your fueling regimen--which fuel sources best work for you and your body and how often to take them.
So, how do you survive the freakout? First, take a deep breath. Then understand it's natural to feel this way. Your brain has all kinds of protective mechanisms, one of which is to tell you that you can't do something. But remember that just because you can't do something now doesn't mean you can't do something after 2 or 3 more months of race training. Can you run 26.2 miles right now? Probably not. Are you supposed to be able to run 26.2 miles right now? Definitely not. It's a process. I had one runner once who, unbeknownst to me, put in a full marathon about 3/4 of the way through his training because he needed to know he could run 26.2 miles before running the 26.2 miles on race day. Well, lets just say that peace of mind, gave him nothing but grief and injury. He ended up not running on race day. You can't do something you're not ready for without risking injury. It's not worth it.
If you're following your training as prescribed, taking rest days as prescribed, listening to your body (and coach) and taking extra rest days as needed, and you're properly fueling and hydrating, then you'll get where you want be on race day. Trust. Believe. Conquer!
Have your freakout. Then move on. You've got a lot of work to do!!