How to know if you have a healthy lungs??

First verb out a letter any letter will do as long as you can don't stop for a breathe of air just keep verbalizing out that certain letter you spoke off,
example:
RRRRRRRRRRRrrrrrrrrrrrrr
rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr
rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr....... now while doing this have a stop watch on your hand, when you stopped and reached you limit. Stop the stopwatch and see how many sec it took you before reaching your limit. 25+ sec your lungs is average, 50+ sec your lungs are healthy,  60+ sec your as fit as a cow, but if you can't even reach 20+ its either your obese or have a weak lungs.