The difference in % is modest enough that it just seems to implie it's not directly 45 degree linear, but has a not that impressive multiplier. Why would vo2max and cardiac output be perfectly direct? After all vo2max also takes into account the lungs and muscles for example.

> The peripheral decline reflects four converging biological processes. Sarcopenia preferentially strips away mitochondria-rich type II muscle fibers. Mitochondrial density and efficiency decline. Capillary networks thin, increasing diffusion distances. And interstitial changes further impair oxygen movement from blood to cell. None of these is catastrophic alone, but together they compound into something substantial.

The (obvious) answer : exercise your body