So it really depends on what % of VO2max we're talking about. An elite runner or someone who is very well trained can run a marathon at 85% of VO2max, or potentially a bit higher. That is a pace that's pretty close to AeT/VT1/LT1, and it's a legit training pace. It's the slowest pace at which you start to see blood lactate climb above baseline and muscle oxygenation drop, which are signals for certain aerobic adaptations. In fact, it's been observed in recent years that blood lactate functions almost like a hormone. In that regard, MP may actually be one of the best bang-for-buck training paces, if your MP is relatively fast. Also, keep in mind that people like Daniels DO NOT KNOW everything that happens in the body in response to training. Nobody does. So just because there isn't a widely accepted model to explain why training works doesn't mean that it's ineffective. In the case of marathon training, there's likely a significant neuromuscular component to this kind of training that isn't well understood yet. We're still stuck with models that focus on oxygen and fuel availability or H+ clearance. On the other hand, for a lot of recreational marathoners, MP may be 75% of VO2max or lower. If that's the case, then MP is unlikely to have much of an effect in training that's distinct from easier paces, and you'd be better off just getting more total volume in at whatever pace is comfortable.
Fernando Vasquez wrote:If you can run 20 miles at MP 4-5 weeks out in a non-race environment then your MP is too slow.
If you CAN'T do 20 miles at MP in a non race environment, then you will never do 26.2 in a race. Whether 20 at MP is a wise workout is another question. I used to do it (and my MP is actually faster than Daniels' chart indicates), and it was fine. Now I go 8-12 seconds/mile slower than MP for the first ten, and MP for the second ten, which feels a little safer.