Jim-
The dives are NOT done on a forceful exhale. It is more like a very gently exhale -- as you read this at your computer, suddenly stop breathing without inhale or exhaling. Imagine a lung volume slightly below that; if you could breath normally, and suddenly stop yourself on the bottom of your exhale (during passive breathing at your PC) that would be the approximate volume.
The reason that you must use a very thin suit or no suit is that one of the main advantages of an FRC (exhale) dive is that you sink the whole way down. Kicking or making effort in the beginning of the dive is by far the most 'expensive' time to exert yourself, because you are draining your O2 supply; kicking on the ascent is more anaerobic, especially when your chest becomes as collapsed as it gets during an exhale dive. With a thick suit, you cannot sink the whole way down, so you lose one of your main advantages. You can do exhale dives with a thick suit, but you won't be able to go very deep.
Alun-
I managed to get some FRC dives done here without a suit a few weeks ago. I seem to sink at quite an ideal speed actually.
Concerning 'convincing' people that it is possible to go 100m+ on an exhale, I agree with Seb Murat that the freediving world will not ever be 'convinced' of this possibility by writing things on paper and making 'theoretical' arguments. The proof is in the pudding. Besides, I would rather people remain skeptical. If only a few people are training this way, then they maintain their advantage. However, what worries me even more is that the 'non-believing' inhale divers will suffer DCS/narcosis/deep blackout accidents as they start going over 100m.
My buddies Peter Scott and Tyler Zetterstrom are also adopting the exhale diving method. Perhaps in 2004 team canada for men will be made up of three no-suit exhale divers
I would also comment that Seb Murat recently discovered that to gain the full benefit of exhale dives, you must completely eliminate any aerobic exercise, as I had previously speculated in an old thread on DB. Aerobic exercise requires thin blood, and so doing aerobic exercise prevents your hematocrit from going much over 50%. Seb says that when he stopped doing aerobic exercise and did only FRC dives/dynamics, his hematocrit shot up to 63% and is still rising. We suspect his myoglobin has similarly increased; another adapation which will not occur in the presence of aerobic training.
Pete and I both have blood analyzers and will monitor our blood each week. I have cut out aerobic training and switched to three deep exhale diving sessions per week (two of them at night after work). My hematocrit is already rising, although nowhere near Seb's level yet. I can confirm Seb's claim that 'mental clarity' at depth is absolutely unmatched. Your mind is as clear as it was on the surface. The breathe up is non-stressful; there will be no critical energy intensive final breath; there will be no packing; who cares about the breathe-up? You won't be inhaling anyway. The descent is relaxing because there is no complicated swimming technique; just equalizing to worry about. The ascent is wonderful, absent of narcosis or feelings of impending 'doom' which I experienced in the old days of deep inhale diving in the cold dark local waters. Further, the recovery at the surface, at the end of the dive, feels totally different, perhaps due to the gradual onset of hypoxia, without the sudden shocking hypoxia that occurs in the last 10m of an inhale dive (when the vacuum effect sucks the O2 out of your blood and back into your lungs).
One thing is definitely certain; if you decide to adopt an exhale diving method, beware of the following things:
1. Lung squeeze: you must already develop flexible lungs from years of inhale diving to significant depths (50m+); you can kill yourself from chest injury if you progress too quickly, and in the beginning, squeeze will be your limiting factor
2. You must already be an expert at equalizing (air mouthfill, frenzel etc..) because it only gets way more complicated at this point
3. Even once you learn to equalize on the exhale, and even when your chest cooperates, expect an oxygen limiting depth of 1/2 your old pb on inhales dives. This is because your blood and myoglobin are still that of an inhale diver. It will take at least a year of hard training (with max effort exhale dives) coupled with good nutrition to expect your non-lung O2 stores to adapt (possibly as much as 4 years for full adaptation if our calculations are correct). Your non-lung O2 stores were seldom stressed in your years of inhale diving, because you always had high oxygen at depth, due to the pressure. Now, without much air in your lungs, your blood & muscles become hypoxic even at depth, and your body adapts accordingly.
Remember that Penguins are not born with high myoglobin. Their myoglobin develops during their first 2 years of life, during which they are constantly diving.
Remember also that on average, marine mammals which inhale (i.e. dolphins, otters) have much lower myoglobin than marine mammals which exhale (seals, whales). Remember also that the marine mammals which exhale can dive much deeper than the marine mammals which inhale.
The sea otter is the marine mammal most similar to humans. It has a very buoyant suit (fur), and it takes a full breath before it goes down. Unlike dolphins, sea otters do not have large sinuses to store the compressed air at depth, and they continue to absorb nitrogen at depth. Like humans, they have very little fat. Sea otters seldom make repetitive dives over 40m, and they will always choose to look for food in less than 40m if they have the choice. The deepest dive ever recorded for a sea otter was 97m -- probably for a reason. The sea otter can dive for more than 10 minutes, so it certainly could dive way over 100m if it wanted to, but the fact that it doesn't means that diving over 100m on an inhale (with its physiology) may not be conducive to survival. Isn't that a coincidence. Inhale divers, take note.
Eric Fattah
BC, Canada