VO2max test

To understand the importance of VO2max, the importance of how it comes from (formula) should be discussed first:

VO2max= COx (A-VO2)difference

CO:cardiac output= HRxSV=heart rate x stoke volume, often referred as central limitation for VO2max

A-VO2 difference: arterial veneous oxygen difference, often referred as peripheral limitation 

To improve VO2max either by increased CO, mainly by increased SV as HRmax reduce or stay consistant as you train, or the improment of A-VO2 difference.

The mechanism of improving SV depends on heart muscle strength/plasticity, end diastolic pressure,ejection fraction,  and increased left vetricular volume 

The improvement of A-VO2 difference mainly comes from mitochondrial content,  capillary to fiber ratio (diffusion distance), metabolic enzyme capacity (beta-HAD ,fat metabolism, CS, carbhydrate metabolism), lactate threshold.