Why would walking up three stairs cause breath shortened, if more lengthy exercises did not?
I am 38, fairly lean (5-8, 148 pounds). Each week, I lift weights 2 to 3 hours, 1.5 hours of cardiovascular exercise (pulse ranging from 125 to 160, depending on session) and walk about 3 to 4 hours.
I can run a long time, without being tired (after 4 to 6 miles, I quit from boredom but I am not tired.)
The problem: walking up three flights of stairs, taking two steps at a time ( I do this about 6+ times a day, at work, going to another floor), slightly takes me out of breath (enough that I have to pause to catch my breath, if talking to someone, within a minute of walking up the stairs.) I am not huffing-and-puffing (never had that even after running 5 miles) but I am breathing more rapidly and as I wrote, can not maintain an even conversation (must pause to get air) for about 1 minute or so afterwards - it is not that big-of-a-deal but since I seem to in very good I am shape, I am confused about it (it is only three flights.) If I only take one step at a time, this is not the case (I have normal breathing then.)
It is not a new situation; I have always had this on stairs, if I take two steps at a time.
Also, even when running or using an elliptical machine, my breath does not seem as short, even with a pulse around 160.
Is it normal or a concern? Does it indicate anything?