Interval training? That's like an uphill portage no? All out, recover at a moderate pace, grab another pack and go again. ;)

At the end of a difficult portage, doesn't everyone take a deep breath and exhale through pursed lips? Isn't that the natural thing to do? It must help otherwise everyone wouldn't do it.

I think I normally do what you guys are talking about throughout the inclines. I expect it comes rather natural to other smokers. Take in all that good stuff in nice and deep and blow it out slowly under a little pressure so it finds/clears every nook and cranny of our lungs.

I'll often inhale through my teeth like a biker though. I get the extra amount of air I need plus it filters out the bugs.