Don,
Missed this thread ... they seem to appear and then dissapear so quickly!
My suggestion would be to keep discussions on exhales under the FRC category.
Some'deeper' insights into boosting the number of red blood cells:
To gain the optimal benefits of 'exhales' from a heamatological point of view there are some fundamental requirements which I suspect may be quite different to those relating to myoglobin (intramuscular) O2 stores.
In my experience, noteable increases in Hct, during apnea, is only achieved when coupled with exercise and warm peripheral conditions, leading to a reduced dive response. That is, there should be minimal muscular fatigue. This is because a patent peripheral circultion will result in more rapid and extensive HbO2 desaturation. Moreover, such a regime can be continued for quite a while before fatgue eventually sets in. This can't be achieved if muscles are cold, since this would lead to excessive waste product accumulation, protracted recoveries and a reduced number of repetition that could be undertaken. My 63% Hct was achieved in this manner, i.e., 50-60 x 50m dynamics in 35" with 35" recoveries / 3-4 times per week for over a year.
With the type of training I've been doing since then, i.e., 1-4 @ 90-100% (ideally 100%) of max effort, I'm focusing on magnifying the dive response in the aim of generating a more prompt and stronger metabolic down-regulation. Although this often leads to extreme muscular fatigue and I can't do many reps, I don't become overly desaturated, which is not necessarily conducive to boosting my Hct. That's ok, however, as I've learnt that max performances don't simply hinge on elevated Hct, but on being able to tap into your muscles, so that muscular failure is likely towards the end of the dive. No one said it would be easy! Correspondingly, doing this type of sensitization training has resulted in a gradual reversion to close to baseline Hct levels but my performances are better.
Seb