I came across some research that said this is actually good, and a sign that in you're in better shape.
The idea is that a fit body quickly perceives the increase in workload, and immediately adjusts all systems to (a) efficiently continue that workload (b) quickly recover from that workload.
The problem is that the body has no way of knowing that you're running up a single flight of stairs, as opposed to 50 flights.
The out of shape body does not respond to the stimulus nearly as quickly. The out of shape body can't continue the effort as long, nor does it recover as quickly.
The idea is that a fit body quickly perceives the increase in workload, and immediately adjusts all systems to (a) efficiently continue that workload (b) quickly recover from that workload.
The problem is that the body has no way of knowing that you're running up a single flight of stairs, as opposed to 50 flights.
The out of shape body does not respond to the stimulus nearly as quickly. The out of shape body can't continue the effort as long, nor does it recover as quickly.