“What this study is actually focused on is something slightly different: VO2 kinetics – that is, how your body’s use of oxygen responds to changes in activity levels. When you go from rest to suddenly pedaling or running hard (as you do at the start of every race or even interval workout), your muscles suddenly need huge amounts of oxygen, and it takes a while for the rest of the body – lungs, heart, blood vessels, enzymes – to kick into high gear. You can measure how quickly the body response to a sudden increase in oxygen demand, which is basically what this graph shows for the six groups:
Again, you’re better off (i.e. you have a faster response) if you’re trained rather than untrained, no matter how old you are. But the big effect that jumps out is the dramatic slowdown in the older untrained group compared to all the other groups. Unlike the VO2max change, this is a change resulting from inactivity rather than age. All the trained groups have essentially the same VO2 kinetics, but sometime after age 60, VO2 kinetics really starts to tank if you’re not fit.
What does this mean? The factors affecting VO2 kinetics are fairly complex, but one key is the blood delivery network. In order to quickly ramp up oxygen delivery, you need to be able to distribute blood; studies have shown that less than a year of endurance training increases capillarization by 20-40%. This could be one of the key factors that you lose with age if you don’t stay fit. It’s probably not going to be the deciding reason that you take up training (“I’ve decided to get fit because I don’t want my oxygen kinetics to decline!”), but it’s a nice example of the many subtle ways that your body keeps working if you keep it fit – and stops if you don’t.”