Cardio-respiratory fitness/VO2 max.
Would you like to know how efficiently your body works? How long and well you can live?
There is an answer: VO2 max reflects “the size of your engine”.
VO₂ max is the maximum (max) rate (V) of oxygen (O₂) your body is able to use during exercise.
VO2 max is often used as an indicator of overall cardio-respiratory fitness (CRF) and can serve as a metric for tracking progress.
High VO₂ max can be a good predictor of your athletic performance and is independent of motivation.
Simply said, VO2 max tells you how quickly you can take oxygen from the air into your lungs, get it into your blood, pump it to your muscles, and then have your muscles use it in the metabolic processes that will provide energy to move you.