Woah there, here comes the science. VO₂ max is the maximum amount of oxygen you use during exercise. Oxygen is used to convert food into energy molecules called ATP, and ATP allows your muscles to keep working as you work out.

Um… ok, so what is VO₂ max? Put more simply, it’s a way of seeing how fit you are when it comes to endurance exercise. The more oxygen you can use, the more energy you can produce. In workout terms, this means the higher your VO₂ max the better. It is generally considered the best indicator of cardiorespiratory endurance and aerobic fitness.

Don’t worry about it too much though, measuring your VO₂ max requires a sports science lab, a treadmill and an oxygen mask, so you may never even discover what yours is.