As we're talking about physiology, not metalurgy, language or music,
then there is only one definition of stress: anything that affects equillibrium or homeostasis in the body, which then effects a change. This is fundamental in physiology, you could say that this
is physiology.
We must also note that none of the changes are free, they use the body's resources.
So minor changes in temperature are a stress on the body, one it can normally cope with quite easily. But, add into the equation, hard training, weight loss, fat loss, physiological and physical adaptations to training in the heat. Now move this body into a colder environment the body will now try to reverse some of these changes(a stress!!)and add an opportunistic endemic cold virus.And we're back to my first post and Jan's cold! I'm not saying that is what caused it, but that cold can be a factor in catching a cold.
Now go back a hundred years or two .... people are undernourished, lack warm clothes, it's winter, it's cold and an old wife is waving goodbye to her old husband on the doorstep. "Don't go out there with your compromised immune system, as it will be further compromised by the low ambient temperatures, and, should you meet someone with a virus you will have no defence and you will catch a .....thingy, what shall we call it? I know a cold, because it's cold and the cold was a factor we'll call it a cold!!"
I love old wives, they were always so sensible. It's the young scientist tales you've got to watch out for, for they have irrefutable proof
"
A very stressed person will still have the same levels of "stress hormones" (such as cortisol) as someone who is relaxed"
...including adrenalin?