It’s hardly surprising for elite athletes to have higher VO2 max scores, but this takes it to an entirely new level.

Your watch’s VO2 max isn’t perfect, but you can improve its accuracy with better data and heart-rate tracking.

VO2 max is an intimidating word for an easy-to-understand biometric: It’s how well your body uses oxygen when you push yourself. Short for “maximal oxygen uptake,” it’s been the gold standard for ...