How much do I need to train to reach my ideal aerobic capacity?
Unfortunately this is a question that has no straightforward answer.
An “ideal” aerobic capacity is “however much aerobic capacity you need to stay healthy given your lifestyle, athletic pursuits, and general life context.” For example, this means that Usain Bolt, who spends very little time in activity (as compared to an ultrarunner, say) needs a much smaller aerobic system to stay healthy: he uses his aerobic system primarily to help him recover properly from his anaerobic work—but that’s just about it. Conversely, an ultrarunner relies on their aerobic system to literally carry them around for hundreds of miles a month, which means that they need a much more powerful aerobic system—one that can support all those hundreds of miles of running and still have enough energy to help them recover and stay healthy.
For this reason, an ultrarunner will have to exercise aerobically many more times a week (and for much longer) than a sprinter like Usain bolt to have enough aerobic capacity to keep them healthy—what is “ideal” for them.
If you’re asking about how much you need to train to reach your maximum aerobic capacity, that unfortunately also depends on the person. A regular joe may need no more than 5-6 hours of training a week to reach their maximum, while a mountain athlete with elite genetics like Kilian Jornet may need four to five times as much training. Of course, in order to get to either of their respective training maximums, the athlete must slowly work up to that over the course of months or even years.
Which leads us to a third question: how much do you need to train for your aerobic system to increase (and continue increasing) in power?
That’s a simpler question, but also with some ins and outs. The super simple answer is: you want to add about 10% of training every week, with an easy week every 4th or 5th week where you reduce your training volume to 40% of the previous week. Another way to say this is that you just need to train a little more than you did last week, for the added stimulus to begin having an impact. However, athletes who are looking for more aerobic power should build up to training sessions that are shorter: 40-50 minutes, to let the aerobic system put its energy into building more speed within that timeframe. Conversely, athletes who are looking for endurance should build up to longer training sessions: 1:30-2 hours, in order to tell the aerobic system to grow more towards endurance. Both athletes will of course improve both in speed and endurance—it’s just that the main training outcome will be different.
In keeping with this, an athlete that is looking for more aerobic power might train 3-5 times per week, while an athlete that is looking for endurance might train 5-7 times per week. But ultimately, how much training frequency it takes for them to reach their maximums in either speed or power is ultimately a matter of individuality: build, lifestyle context, and genetics.