Notes
goal was 90-95% tempo or medium tempo. That is to say 5-10% slower than goal marathon pace. (Keep in mind 4/5 miles were run above 9000 feet elevation. It would have been faster down low.) The goal of this kind of workout is to run at a rate that is close to the maximum aerobic lipidic power or aerobic fat power. The purpose is specifically targeted to help at the end of the marathon. When we run some of our energy comes from lipids (fats) and some comes from carbohydrates. Since humans can not run the marathon in around one hour yet we still need to use fats to help get us 26 miles to the finish line. As an example say that it takes 100 calories per mile at the desired pace. Pretend that an less desirably trained person uses 75% of those from carbohydrates and 25% from lipids. Now imagine that only 1800 calories are available for the race. That gets the racer to 24 miles then there is a wall because there are no more carbohydrates. And even if there are maybe there are only 50 available and some of those are for the brain, heart, lungs and those things.
Now if that runner had trained to process more fat during the race so that 70% was carbohydrates and 30% was fat then that gets the runner to 25.7 miles within a half mile of the finish line before bonking. If that person was successful in taking in 35 calories of carbohydrates during the race then he or she would get to the finish line just in time. (Keep in mind that only a small percentage of calories consumed within a 2-4 hour race have enough time to be processed and actually used.)
If you watch marathons you will see that there are usually a lot of place changes in the last few miles. People are hitting the wall left and right and someone who started slower or trained better will be passing those people. You could call it carbohydrate management. The ability to run at a pace, take in enough calories during the race