If you want to geek out on this a little, read these two threads about training for fast-twitch vs slow-twitch runners. On the first one, you can skim through the first few pages where Cabral waxes on about some historical stuff. But, fundamentally, this is directly on point and it's really interesting how two great Portuguese runners -- Mamede and Lopes -- ran very similar times over 5,000 and 10,000 but Mamede was originally a 400m runner and Lopes was an aerobic monster and they trained very differently. A similar comparison is made to Webb vs Ritz. The short of it is that a FT runner training for longer distances is better off doing controlled, long intervals instead of hard tempos and with short, jogging recoveries (if too long and/or walking, your anaerobic engine will recover too much). As an FT, you rely heavily on your anaerobic system when you race and even in the really hard tempos, so are getting the wrong stimulus from the latter which will degrade your racing over the season. Here are the links and below them are an excerpt that is on point:
http://www.letsrun.com/forum/flat_read.php?thread=2375989
http://www.letsrun.com/forum/flat_read.php?thread=2666852
"From a friend of mine…
I just read the last few posts on the LRC thread, and I agree 100% with your final post (that FT runners are more irregular in their performance). I think the reason for this is that it is very easy to get the intensity 'wrong' when training these runners, as great control is required in all training sessions to ensure that sessions that are supposed to be aerobic in nature do not end up being just a little too fast and therefore anaerobic. In particular, an FT type in good shape can easily go a little too fast on a tempo/ LT/LTP session because the pace feels so slow.
I think it is easier to train an ST type because there is more margin for error (I think Hadd touches on this point in the thread). An ST type is able to run short reps quite hard and get away with it, because they produce so little lactate as a result of having so few FT fibres. An FT runner though needs to be very careful as going too quick will soon result in large increases in blood and muscle lactate. You think that FT types benefit from intermittent workout sessions instead of traditional continuous threshold runs, and my experience also suggests this is true. I think the reason for this is simply that it is a safer way for an FT type to do this type of intermittent training as the short recovery periods allow enough recovery to clear any muscle lactate that may have been produced as a result of running too quickly. The FT type could probably still benefit from the LT/LTP session in a continuous format, but they would need to be extremely accurate in pace control in order to prevent the session becoming 'dangerous'. "