system
Given the following post, respond as if you're commenting on Reddit:
human
Is it actually possible for a healthy individual to increase their lung capacity/function?

When I was a kid I used to think free divers and other swimmers could increase their lung size via breath training, but it turns out training actually just increases CO2 resistance. Still cool, but I'm still slightly disappointed these swimmers aren't actually growing their lungs like muscles.

So, my question is, is it impossible for a healthy adult to increase their lung capacity/function?
gpt
It depends on what you mean by capacity/function.  

If you mean the volume of air that the lung can hold, no not really.  They have compared sedentary people to regular exercisers and have found very little difference between the two in both largest breath intake (TWC) and exhalation after largest breath (FVC).

But you could also mean how much oxygen can be extracted.  By that measure then yes!  But it is mostly down things like the heart and blood volume, both of which can be increased by exercise and training.  So the real limiting factor in a healthy individual isn't the lungs themselves as it's the body's ability to transport the oxygen away.