Running and the Stress Response

One of the things that has always puzzled me about running is how it triggers the stress reponse.  If you run sprints or intervals, this triggers the stress response but that is what is supposed to happen.  However, even doing slow running (jogging), I've noticed that it triggers the stress response for me.  Then the longer duration of a jog compared to a sprint seems to make things worse, because you have a longer continuous period of stress.  What doesn't make sense is that the jogging is low-intensity like walking, and somehow walking doesn't trigger the stress response and yet jogging does.

Something that may help circumvent this problem is nasal breathing.  I did another easy run with nasal breathing last night, and I felt fine today.  The root to this may be biological - many animals usually breathe through their nose, and then only under stressful conditions (like being chased) do they breathe through the mouth.  The same may be true with humans.  Running with nasal breathing may signal that everything is still okay, while running with mouth breathing may trigger the stress response.  This is just a hypothesis, but I will continue to work with it and see if it's true.