The measurement of your cardiovascular fitness is typically referred to by many as measuring V0-2 max; V0-2 max is the body’s maximal
ability to utilize oxygen to perform work. In actuality, there are very few people who can voluntarily work hard enough to reach their V0-2 max... This is because V0-2 max is exactly what it means; Maximal work output, just before complete physiological crash, and not voluntarily sustainable for any meaningful period of time.
Actual measurement of V0-2 max outside of a clinical setting can be extremely risky, due to scope of practice issues, as well as the need for the emergency equipment required. In a health and fitness setting, V02 max is typically plotted from extrapolating the results of a much safer sub-maximal test, such as a physical work capacity test on a bicycle ergometer or treadmill. However, a V02 max test is a poor choice for answering the more practical question that people really want to know, which is; What is their maximal sustainable cardiovascular ability to perform exercise?
A term known as V0-2 peak is a more usable measurement of cardiovascular fitness, as it pertains to the body’s ability to perform a maximally sustained aerobic effort. From a heart rate perspective, it is very close to and just prior to something called metabolic acidosis, in which the level of carbon dioxide being produced by the body begins to exceed the amount of oxygen the body can physically take in, which in turn quickly leads to V0-2 Max.
The difference is that V02 peak represents a voluntary maximal effort. Therefore, V0-2 peak is a more usable, real world measurement of cardiovascular fitness. The ultimate goal is more efficient fat utilization by the body over time, which leads to more effective weight loss and a higher level of cardiovascular fitness.