You might be surprised.
Crossfit Endurance is a group of endurance athletes, Ironmen and ultramarathoners who believe that LSD does little more than slow us down and make us look like a bunch of overaged, emaciated drug addicts. I don't know about the drug addict part (I look more like an overaged beer drinker), but I have preached for years that too much long slow running will turn us all into long slow runners.
Consider this quote from Crossfit Endurance specialist, Brian Mackenzie:
While our approach starts with mechanics, it is based on strength and conditioning... Or CrossFit. The endurance training is a supplement. Our athletes eat the conventional endurance geeks for lunch every time... And we have story after story that explains how their friends either stayed the same, got slower and can't walk after the race. When we are the exact opposite. On almost a 1/3 of the training. How is this not a better approach?
Endurance geeks? And this teaser from the Crossfit Endurance site:
Why should I start training this way?
Are your times CONSISTENTLY getting faster at ALL distances (what was your last 5k time compared to a year ago)?
How high can you jump? (Many marathoners cannot jump onto a 12 inch box).
How many push ups/pull ups/squats/etc can you do? We can do more.
Have you or are you suffering from chronic use injuries (plantar fasciatis, IT Syndrome, runners knee, etc)?
How many hours do you train a week? How many hours does your spouse/family wish you trained? (This program only requires 6-8 hours per week to COMPETE at Ultra/Ironman distances.
Hmmm. Want to learn more about how running shorter and faster *could* make us better ultrarunners? Conditioning Research has a nice post on this very subject.
From my own personal experience, I've incorporated more "crossfit" style workouts into my overall training in the last year, with positive results (e.g., PRs at some tough races, more muscle, less fat) averaging just under 40-miles of running per week. That doesn't prove anything, and I'm not about to give up those epic-long training runs, but I am sold on the idea that too much LSD makes a long slow runner.
Try it for two weeks, and judge for yourself. I'll post a daily workout (not Crossfit per se, but something along those lines), follow along if you want. You might be sore at first... but soreness turns into strength. Strength turns into PRs in running, and other places too.
Run hard out there, and run long too. But run harder more than you run longer.