howarde:
Thanks Mark... It still seems a little vague. This report says to wait six hours, so I guess total desat isn't required? For example... I've been out of the water for 6 hours now, and my computer says I won't desat for another 10 hours, so according to the undercurrent article, I should be ok to go workout now (not that I'm going to... I think watching a movie is more in order for this evening) but in the DAN study, it talked about the Nitrogen Bubbles being like a bottle of soda. Whereas excercise would shake up the soda bottle, thus increasing the risk for DCS. Which sounds to me like you should be completely desaturated.
Howard,
To answer one of your earlier questions, heavy lifting would be worse than moderate aerobic activity post-dive because it has greater potential to generate cavitation (bubble formation) without the benefit of increased peripheral and pulmonary perfusion (that eliminate both dissolved gas and bubbles) that you'd get from aerobic activity. In fact, aerobic exercise post-dive has been shown in two studies to increase bubble elimination, though earlier studies have found that it increases risk of DCS. Hard to tell who's right on this.
In truth, we don't need to fully desaturate to exercise- we only need to offgas enough that the bubbles we create don't overload our abilities to eliminate them fairly quickly. The question then becomes, when do we reach this point? The short answer is, who knows?
Decompression (or desaturation, as you put it) is an extremely variable process. Do the same dive profile on two different days, and you body will end up with two different amounts of nitrogen absorbed at depth. The difference can be quite substantial, depending on activity level on the dive, how cold you are as you ascend, etc.
When you surface, you will also eliminate that gas load at different rates depending on your activity level, body temperature, hydration level, etc. So, again, 6 hours after the same profile on two different days may find you with two wildly different levels of gas still in your tissues. So, dive tables and computers like yours have a built-in safety margin since they can't really determine what your true gas loading is and how well you are eliminating it once you surface.
Coming back to your original question- do you really need to wait 10 hours to exercise after diving? DAN's recommendation of 6 hours seems to be working for divers who come out of the water otherwise feeling fine after normal, recreational profiles.
That said, it is much more preferable to exercise *before* diving, whenever possible. As long as you prevent dehydration and excess fatigue, exercising before a dive is much less risky and might even be beneficial, though researchers still have much work to do here.
Cameron
