A friend of mine and I were trying to figure this out at lunch today. Why do we spit when we get tired? He was taught that in football; you could tell when the other team was getting tired from two signs, 1) they started putting their hands on their waists and leaning over, and 2) they started spitting.
I then realized that I carry a water bottle with me when I do energy systems work, and there is a point where I stop drinking the water and don’t want to swallow. I swish it around in my mouth and then spit it out.
The only thing I can think of is that the blood flow to the stomach and internal organs is reduced to provide more blood flow to the skeletal muscles in heavy exercise. Then the stomach doesn’t want to take in anything, including excess saliva. Any better ideas?