Consider two runners who, in lab testing, have identical values for VO2 max, running economy, and lactate threshold. These are the three quantities in the “standard model” of endurance performance; you can plug them into an equation to calculate your expected marathon time. So who will win the race?
The question is not as hypothetical as it seems. At the top end of the sport, athletes tend to have relatively similar values for all three of the parameters. And if they’re weak in one, they’ll compensate in the other two. And yet lab testing isn’t capable of reliably picking winners. The cyclist with the highest ever VO2 max flopped as a pro; the top marathoners that Nike picked for its Breaking2 marathon, including Eliud Kipchoge, didn’t have unusually high lab numbers. There’s clearly something missing from the equation.
Over the past few years, researchers have zeroed in on a suspect for what one paper calls “the fourth dimension” in the endurance equation. It has various names: durability, physiological resilience, fatigue resistance (which is the term I used when I first wrote about it in 2021)….
