Wow! You forget to breathe when you speak English. It is amazing. I am wondering if the same thing happens when you speak Japanese.
Regarding your incredible lung capacity, I collected the information on the Internet. Since I have not read them thoroughly, I might be wrong.
Here is my theory; Everyday walking brought you an amazing outcome on the vital test, I think. Walking is an aerobic activity that strengthens respiratory muscles, and that can help to improve cardiorespiratory function. As a result, the lung capacity increases.