I confess: I used to run my long runs way too fast. I did every long run as hard/fast as I could with the thought process that running that pace during my long run meant I would be capable of running that pace for a race. I did this for several half marathons and even my first marathon (still my best marathon time, but let's ignore that for now).
This past training cycle, my long run pace ranged from 10:30-10:50. There was one magical unicorn long run day where our easy long run pace was 10:18, and one long run with a workout in it (a couple of miles at LT at the end of the run) that had us running right around a 10 minute pace. Yet my pace for the Brookings half marathon was a 9:33. 60-80 seconds per mile faster than my long run paces.
Since I started running distance back in 2005 (uff da, that's forever ago!) I've read a lot of books and articles about endurance training principles. What can I say, I'm a nerd and want to learn whatever I can about what I'm passionate about! One of the principles that resonated most with me is heart rate training, which is essentially training your heart to work more efficiently while you run. By running slower you are able to increase efficiency, so over time, you are capable of running faster without running harder. It's not any fun at ALL to start heart rating training, because you have to slow down. A LOT. To keep your heart rate in the correct zones for the various types of training runs. But once you dedicate some time and effort to it, it's awesome to see the benefits.
I think so many runners would benefit from slowing down their long runs, reaping the heart rate benefits and establishing time on their feet. An occasional faster finish, or a long run with a couple of minutes of pick ups throughout once a month is fine, but when we essentially "race" our long runs, not only are we not getting the endurance benefits from the training run, but we're also causing our legs to have to recover as if they've raced every weekend that we run long. And then we're also asking our legs to run hard and fast during a speed session during the week as well.
I spent a lot of time this winter base building aka a lot of slow mileage. Eight week of dedicated base building before I started a training plan and then an additional 4 weeks of base building within the training program. To say that I was ready to have some workouts when week one million hit, would be an understatement. But I found that the 12 weeks of base building really helped to lower my "easy" pace on runs, without doing anything but keeping my heart rate in the correct zone when I was running. And once our workouts started, I was continually surprised at how I was capable of hitting paces that were so much faster than what I was training at, and my legs were recovering well and quickly from the runs. It's almost... as if it's magic! Or science. Definitely one of the two.
If anyone wants some heart rate training reads, I would suggest either of Pete Pfitzinger's books. I also have an awesome 21 page document that someone sent me forever and ever ago, and it's super insightful and written in a very easy to digest way (despite it's length). I'm a convert, and I think others should be too!