Hey Dave - I'm going to read over the questions again later this week and think about it, see if my answers change. I still felt compelled to answer now so here we go. 1. - I feel this is quite contextual, based on the current state of the athlete. It could either provide a parasympathetic response during and or after. I feel it could do the same with a sympathetic response during and or after. Perhaps it depends greatly on the current state, goals and experience of the practitioner. If a person has been busy all day for example but is dealing with something causes emotional stress - it might arise during the exercise so it could create an adverse (Depending on the intention of the exercise) reaction since said person hasn't created the time to allow these emotions to arise during the day for example. I'm going off on a tangent on this one, provoking question! 2. Spo2 would more than likely remain within 95-99% although you didn't mention if the athletes would be completely static, if they were to start moving - this could change things. But given the nature of a static person not using much oxygen and the apnea cycle being quite balanced between in an out I would assume the spo2 would remain between 95-99%. 3. Reflection of your current output ability of energy. - A simplified way of looking at it could be that it is a reflection of how much c02 your body can handle at that specific time before drastically changing your breathing volume and intensity. 4. How much they are both willing and able to do. Love these discussions Dave. And Like I said these answer were kind of done in a hurry, just came back home from training and a full day of work, ready to eat :D Cheers.

Just did the exercise and it was stressful for me, even got diaphragmatic contractions on the exhale. I do like to do stress inducing breathing exercises after theoretical learning though, it helps retain information. (paraphrasing; It could have something to do with the brain wanting to retain information about your environment after a stressful event.)