If your goal is to run a 7-minute pace you need to do a lot of 7-minute-paced running. Not 8 minutes and not 6 minutes. There is this thing called “economy” which relates to the principle of specificity. If you spend a lot of time running 6- or 8-minute pace you will not be as economical at 7 minutes as you could have otherwise been.McCrann points out that "your body will only adapt when it is challenged." Yup, got it. Your body is basically lazy. If you pick a pace and only train at that pace, you body adapts to that pace, so instead of leading to increased economy, if you continue at that pace, it actually decreases economy due to lack of training stress. I loosely (very loosely) am describing Progressive Overload, here, and while training at a certain pace will increase economy.
McCrann isn't the only one to challenge Friel. Chris Whyte points to a number of studies that support Progressive Overload on his blog, The Running Economy Myth, and challenges Friel's notion of specificity in training. According to Whyte:
No matter how you look at it, doing a lot of running at goal race pace, by itself, is not a factor in improving your running economy. It can only become a factor when the stimulus associated with training at goal race pace just so happens to be responsible for creating an overload and therefore eventually inducing an adaptation.Basically, we have to train our bodies to use less oxygen when we run to become more economical at a given pace. By more economical, I mean, use less energy given your output. The way we teach our bodies to do that: push ourselves harder, faster, and further.
Whose side to I fall on? Well, to be a complete spineless wuss, I kind of like a little of what everyone is saying. I agree that specificity alone does not improve running economy, but I am not prepared to throw out the years of experience and knowledge that Friel has to lend by any means, but I am also not a blind follower who doesn't listen to any other ideas either.
I am no scientist, I am certainly no expert. Training is a very individual thing and generally, there is not one good answer that fits every athlete. I tend to read a lot of different ideas and mesh them all together to do what works for me. But what I do get out of this is that pushing yourself more will lead to bigger gains in the long term.
Note: Friel does recommend intensity work, just not everyday - something both blogs challenging him failed to mention. Pushing hard is important, but not everytime you go out because 1) you risk injury, which would be a big step backwards in your training, not a gain, and 2) you need recovery to improve. So in the end, I want to amend what I wrote earlier to say I fall firmly on Friel's side on this debate, understanding the importance of pushing yourself harder with intensity work as specified under a training program of the athlete's (that's you!) choice.