LA/Pure running wrote:
... So, in essence, you're doing a speed workout while going slow." Let's say that WAS true(and of course it is not...
LA/Pure running, read JK's long run procedure again. He says to pick it up at the end of the run. It's not jogging. He also recommends doing strides - some of them faster than 5k pace - within the last mile of some of your long runs. While it might be true that long slow running by itself doesn't cause FT fibers to be recruited, picking it up or doing strides absolutely does cause fibers that are closer to the FT end of the spectrum to be recruited. You might ask why you have to log a bunch of miles on the run prior to starting the faster running or doing the strides. That is, if you're going to do 17 miles with the last 5 picked up, why not just skip the first 12 miles and go right into a 5 mile fast run? Well, I'm just a grad student in ex. phys., so I'm not at the cutting edge of the science, and maybe Phoenix or somebody else can chime in, but it seems that since both the ST and FT fibers become depleted during long runs, there might be some additional stimulus to increase enzyme activity in the type II-b fibers once they are recruited from the pace pickup at the end of the run. It's very clear from actually doing long runs where I pick it up at the end that I get much stronger all the way down to 5k pace or even faster, although (as you point out) my pure sprint speed isn't improved any. There must be some additional boost toward making those FT fibers oxidative that you get from a pace pickup at the end of a long run that you don't get from a 5 mile fast run by itself.