Maximal oxygen uptake (VO2max) is the primary marker of cardiorespiratory fitness, representing the maximum oxygen the body can utilize for physical work.

“vo2 max is the one physiological parameter that anyone who's involved in endurance has heard of and has some sense of the first order analogy is it's kind of the size of your engine physiologically vo2 max is telling 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 to do whatever you want to do so it's a rate it's how much oxygen per unit time can you process absolutely flat out”

“there's a plateau there's a point at which even though you're working harder you're not using any more oxygen and so this plateau looks like it's a physiological limitation and it probably is in some you know it's a controversial thing but basically you've reached a point where no matter how hard you push yourself you can't get more oxygen and so you can still go faster because you're starting to use other forms of energy but this is the limits of your aerobic system this tells you what it tells you what we can get into it's not clear what it tells you it tells you exactly what i just said it tells you how much how much oxygen you can use”

“So VO2max is the maximum rate of oxygen uptake by the body. It's typically measured during an incremental exercise test. So you get up to very high work rates and that's where you'll see your highest rate of oxygen uptake. It's determined by many physiological factors and processes, but it reflects the peak integrated capacity of the cardiovascular, the respiratory, the blood, the skeletal muscle system to take up and utilize oxygen.”

“the simplest is the maximal oxygen uptake that's the maximum amount of oxygen that can be taken in from the environment brought into the body by the lungs transported by the heart to the skeletal muscle and used to do physical work it's the exercise physiologist marker of um uh Fitness and so when we hear the term cardiorespiratory Fitness that's what we really mean”