The Marathon is considered the pinnacle of human performance, and in addition to this, humans can run the fastest marathon of any species. So, how does one train for the ultimate race?
Our ability to run a marathon is largely influenced by four main factors, VO2 max (your maximal oxygen uptake), running economy (amount of oxygen used at average marathon velocity), Lactate Threshold (LT - when lactic acid accumulates in the bloodstream), and available fuel sources (i.e amount of carbohydrates or fats stored). VO2 max is predominantly genetic, therefore, adaptations through training are limited (5%). As a result, it makes senses to focus training on dealing with the metabolic demands (how efficiently the body uses available fuel sources), increasing running economy and LT.
Midgley et al (2007)
At the top level, marathons are run at 96% of critical speed (a similar measure of LT). In addition, LT is considered the best predictor of endurance performance (R values are often 0.88 and above - very strong correlation). Meaning, even if you have a lower VO2 max with the right training you can buffer blood lactate levels by up to 10.3%.
Progressively, what sets humans apart from other animals when it comes to marathon running is are thermoregulation (maintaining homeostasis). A by product of exercise is heat production, which must be transported to the surface of the skin. The body does this by vasodilating (expanding) the arteries and bloods vessels, and as a result sweat is released from the plasma of the blood. However, the problem with this is you lose sodium (an important electrolyte) through sweat. Furthermore, during training, sodium concentration of sweat increases and they re-enter the body through the reabsorption glands (Eccrine glands) leading the electrolyte back into the bloodstream, thus improving thermoregulation. Which is a key feature in humans that allow us to run further than any other animal.
So how do you consider all this when training?
Unsurprisingly, to increase your LT you will need to endure a bit of pain. Intervals above your Functional Threshold Pace (FTP) can offer improvements 2.5% higher when compared to intervals at threshold.