am) 14 miles-HR avg. 145. It was freezing! It felt like 0.. pace was strong and legs felt good.
pm) 10 miles-HR avg. 143. It was no warmer. Legs felt better and better as this run went along. I felt good enough to run faster but want to save energy for tomorrow's specific block.
Ironboom asks - "Lucho, I noticed that every now and then, like last week, you opted to do two shorter marathon specific runs versus one long one e.g., 24+(though you also did a long easier run). I'm guessing breaking the run up into two decreases risks of injury, while, if completed in the same day (within a several hours?) mimics the physiological, musculoskeletal, cardiovascular adaptations of running long at marathon specific pace. But you have also done those specific runs while running long. Would you mind discussing the costs/benefits re the two and describe your thought process when opting for one versus the other from week to week. Thanks."
Excellent question and I will answer as I understand the different benefits.
You are right in that the longer single run stresses my musculoskeletal system in a way that is specific to the marathon- tendons, bones, muscles. Once the length of the run reaches a certain time then there is a metabolic benefit in terms of lipid consumption and lactate production. This type of run is important but not necessarily the most important. Once an athlete reaches an adequate state of fitness then it is best to simply maintain this and switch to a more specific training stimulus.
Marathon training should be designed to bring your AeT pace per mile (2.0 mmol/ lactate) as close to your LT pace per mile as possible. It has been observed in elite runners a velocity difference of only 4% but a typical (middling elite) runner's disparity is closer to 7%. In order to do this one must have the ability to digest lactate at a high velocity.. ie: if I run at my LT then I want to be able to back off to my marathon pace and actually lose (digest) lactate from my blood stream... and I want said marathon pace to be as fast as possible. A single long run needs to be structured correctly in order to stimulate this metabolic function. More specifically- a progressive build to marathon pace towards the end of the run or doing intervals at slightly above marathon pace (~103%) alternating with recoveries no slower than ~98% of goal pace. Part of what I am seeing with my own training (which is an experiment on myself as I have no guidance) is that I am often too fatigued to perform a long run with the structure mentioned above. It's also difficult with out Chuck here to ride support and provide the proper nutrition and hydration that is key. So...
I perform a workout called the "Special (or Specific) block" which you refer to in your question. The goal of this run, and I refer to it as A run because the benefit of one only exists because of the other, is to deplete my body in a specific way to the marathon. The morning run depletes my blood lipid and muscle glycogen stores. The second run, done at goal marathon pace also, is hopefully going to teach my body to preserve glycogen stores and favor lipid consumption. The over-all pace of these two runs is much higher than if I ran a single run and is also (as you surmised) less stressful from a musculoskeletal stand point.
There are books written on this subject and my answer probably will make any knowledgeable physiologist roll their eyes. The limited knowledge that I have in regards to the technical aspects of this methodology is counter balanced only by my ability to execute it..