I am sorry if this is not appropriate for this site, but I think it fits so I am asking it here:
I went for a run yesterday, and it was about -8 degrees Celsius. I was wearing a couple pairs of shorts, a t-shirt and a long sleeved shirt, which is not that much, so I went with the idea that I would warm up a lot while running. After running for a while, I found that I was tired and out of breath much earlier on then I would normally be. It raised the question:
How does decreasing the ambient temperature affect the cardio vascular system?
There were two things I could think of that might directly affect it. (1) The fact that my body's metabolism has to work to heat itself, and this takes energy. However I am not sure how much of a role this plays since running warms you up anyway. (2) The air being so cold, and entering the lungs, I imagine my body has to work much harder in some way to deal with it. What exactly happens here, and how is the process different from breathing at 25C?
Also, how much faster would we expect a runner to be able to finish a 10km run when it is 25 C outside versus -5 C outside?