I've been lurking here for a while and I've noticed that a common response to questions about belly pooches is "cortisol." From what I see here, on Mark's Daily Apple/Archevore/ other paleo-oriented websites, cortisol is elevated through stress that's both physical and psychological. The confusing part is that people are sometimes then told to reduce the HIIT and replace it with weight training, but I don't see how that works. I can see how the following scenarios work:
Lack of sleep - body is stressed due to lack of rest, cortisol rises
Crummy boss/workplace - cortisol rises as part of a fight-or-flight response
Enraged saber-toothed tiger ten inches from your butt - that's true fear.
HIIT - the heart rate rises, true, but a Crossfit metcon isn't necessarily a stressful situation. There's nothing life-or-death about it and I know that I can simply walk off mid-workout if I choose. There's no forced psychological component other than the self-imposed one. (Burpee penalties for quitting aren't true psychological stressors either.)
In weight training, the heart rate soars for brief(er) periods too, especially during sets. So theoretically that'd contribute to cortisol elevation too.
So, why does HIIT contribute to cortisol elevation but weight training doesn't? Is cortisol raised purely when the heart rate is elevated, regardless of the cause?