M.F.: Fred, thanks so much for letting me know about this. You've just given away another one of my secrets - one that is usually only taught at my annual seminar.
I must have kept this because I was like 'cool, I may have Combat Abs, but this isn't in there and I'll never go to any of his seminars, so free info. I hope you all like it too. What do you think? Now obviously, what this guy is talking about is doing a vacuum while in the Downward Dog position of yoga that is the starting point of the Hindu Pushup. This would be a great thing to try while doing yoga too.
Normally, in yoga, the vacuum is done while done while flexing the spine on all fours. I still think this would be more effective specifically for the muscle used in a vacuum, because then it is pulling directly against gravity. While in downward facing dog, you're still working against it, but on a bit of an angle so it wouldn't be as intense (I know my physics). One of the benefits, though, is that unlike in the spine cat stretch (or dog stretch, whatever, I see my cat do it anyway), other abdominal muscles are being engaged at the same time. Perhaps this increased pressure in the abdomen makes the vacuum tense harder due to tension irradiation (Pavel Tsatsouline theory, seems to make sense), plus it would put wonderful unique stresses on the internal organs to aid in purging of toxins.