Why can two runners with the same VO2 max finish a marathon minutes apart?

Because VO2 max, the size of the oxygen engine, is only one of three things that matter. In 2020 a team led by Andrew Jones at the University of Exeter, thinking about the sub-two-hour marathon, named three physiological factors: a high VO2 max, excellent running economy and a high lactate threshold (they called it the lactate turn point).

VO2 max is the most you can take in and use oxygen at full effort; elite runners can exceed 90 millilitres per kilogram per minute. But it can be a poor predictor of runners' performance, because of differences in running economy and fatigue resistance.

Running economy is the fuel economy: how little oxygen you burn to hold a given speed. Runners who consume less oxygen at the same velocity are more economical, and among trained runners with equal VO2 max values it correlates better with performance.

The lactate threshold is the point where the muscles start making lactate faster than the body can clear it. Below it, the body clears lactate; above it, lactate builds up. Endurance training raises it.

Put it like a car: the engine size, how hard you can drive it without it overheating, and the miles per litre. Two drivers with the same engine can finish minutes apart.