https://onlinelibrary.wiley.com/doi/full/10.1046/j.1365-201X.2001.00871.x

So, San Millan pointed out that MCT-1 and MCT-4 are important for clearing lactate, and he said the way to increase MCT-1, which are in slow twitch muscle fibers, is through Zone 2 training. Maybe there are studies that back up that claim, but I found this one, linked above, with Nordic skiers, that doesn’t necessarily seem to fall in line. 

Researchers looked at muscle biopsies after 5 months of training at either moderate or high intensity and found that MCT-1 fell in the moderate group and didn’t change in the high intensity group. You would think MCT-1 would have increased in the moderate (60-70% of VO2 Max) group, according to San Millan’s claims. I didn’t buy the study, so I can’t look at the full results, methods and/or discussion, but even just judging off the abstract, the results were kind of surprising when compared with San Millan’s claim. 

I think, as you’ll see on Monday’s show, San Millan brings many important points to this discussion of lactate threshold. If I disagree with him on anything it would probably be this: 

Just because theoretically, MCT-1 exists in the slow-twitch muscles, and therefore LSD training will increase MCT-1, it doesn’t necessarily follow that someone could just do a bunch of LSD training and still be really effective at clearing lactate and running fast.

Say I needed to build a hole in the ground. If I have two groups of people — those digging (MCT-1) and those carting the dirt away (MCT-4) — training LSD all the time to increase the number of MCT-1 is like bringing 1,000 workers to dig to the site. But, just because they are present, doesn’t mean they know how to dig, right?

Isn’t there something to be said of actually ‘practicing’ lactate clearing by training at an effort that requires lactate clearing to take place? (i.e., maybe I do less LSD, only have 500 workers at the site, but I know these workers can actually dig holes).

In other words, I don’t think you can do 70-miles of running per week at 8:00/mile pace and then hop in an 800-meter and expect to run 1:51 – even from a metabolism-standpoint (and that’s nothing to say of the other elements which go into that type of performance, like running economy, biomechanics, natural speed, flexibility, mental toughness, experience with pacing, etc.)

San Millan seems to suggest that you really only need two training zones – long, slow stuff and short, fast/hard stuff. This might be true with athletes who are either very young or who run races like the 800/1500, but it seems like there is more to the puzzle. 

I’d like to see some more studies, and I don’t doubt their existence, which show how certain types of training increase MCT-1 and MCT-4. Until then, I’ll probably just “go kinda hard for the next 20 minutes” periodically in my rides, runs and skis.