i presume the sedentary little old ladies and men are not keeling, so you should go have tests done. delta is not depriving you of oxygen.

i have had every shortness of breath test and lung test ever devised. the idiots(find a better word), never determined i had an blood clot in my leg, was throwing debris into my blood stream causing minor pulmonary embolism. a friend who is a pediatrician suggested it.

i also thought it was recommended to take long deep breaths when suffering from hypoxia, not shallow fast breaths.

when you do cardio, do you monitor your heart? omicron makes a nice inexpensive heart monitor.

you should start pushing the upper limits of your heartbeat, for at least 30min(with cardio supervision).

i play squash with a pulse of 150.......i'm 74 years old. don't try this on the first day. at 50, you should be able to run somewhere between a hundred, and 150, once you become a "trained athletic"