From the sound of it, you seem like you enjoy what you are doing and have been climbing stairs for some time now. If you are worried about the wear and tear of your knee caps, you need to take a few pointers into consideration:
· If you or your family has a history of joint problems, then it be wise to lessen the amount of running up the stairs.
· The technique you use to take 2 steps at a time requires that you do not excessively bend your knees more than 90 degrees. That way, the knees will not get too much tension, which will prevent them from early wear and tear.
You can also think of alternate methods of keeping fit (in your case, the benchmark has been not running out of breath) brisk walking, jogging on a soft surface (with good supported shoes), cycling and swimming are some of the activities that will give you similar benefits (improvements in cardio-vascular health).