VO2 max is the maximum rate of oxygen your body can consume during intense exercise. Higher max, the maximum oxygen amount usable during intense exercise, significantly reduces "cardiac age" by improving heart efficiency, increasing oxygen capacity, and lowering all-cause mortality.

Regular, particularly high-intensity interval training (HIIT), can improve VO2

max by 10–30% in older adults, effectively reducing cardiac age. The Norwegian 4x4 protocol is a highly effective, research-backed, high-intensity interval training (HIIT) method designed to rapidly increase max and cardiovascular health.

To directly increase your maximal oxygen uptake, you must train in the VO2 Max Zone, which is typically Zone 4 or Zone 5 depending on the model you use.