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Exhaling or inhaling air before the dive: what's better for humans?

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New Member
Oct 3, 2002
I don't know the answer to this question. But I read the following statement in a reading regarding the physiology of cetaceans:

Some of the adaptations that make long dives possible are as follows:

1. The oxygen combined with the hemoglobin of the blood and with the myoglobin of the muscles accounts for 80-90% of the 02 supply utilized during prolonged diving.

2. Arterial networks seem to act as shunts, maintaining the normal blood supply to the brain but effecting a reduced supply to the muscles and an oxygen debt that the animal can repay when it again surfaces.

3. A decreased heartbeat further economizes the available 02.

4. The respiratory center in the brain is relatively insensitive to an accumulation of carbon dioxide in the blood and tissues. The hydrostatic pressures encountered at great depths are alleviated by not breathing air under pressure and by the permeation of the body tissues with noncompressible fluids. The only substances in the body of a cetacean that can be compressed appreciably by the pressure of great depths are the free gases, found mainly in the lungs. The collapse of these gases drives them into the more rigid, thick-walled parts of the respiratory system. The body temperature is regulated by the insulation of the blubber, which retains body heat when the animals are in cold water, and by the thin-walled veins associated with arteries in the fins and flukes.

Just comparing some of the physiological adaptations of humans vs certain cetaceans:

Myogloben Concentration & O2 Carrying Capacity:

1. Myogloben (g/kg muscle): Human (6.0), Sperm Whale (56.7), Weddell seal (44.6).

2. ml O2/kg muscle: Human (8.0), Sperm Whale (76.0), Weddell seal (59.8)

So diving mammals have a huge amount of oxygen stores in their myogloben compared to humans.

And my question again is if it's better inhaling or exhaling before diving?

Regards, gerard.
Well, other aquatic mammals exhale before diving to attain neutral boyancy.

We don't have nearly as much fat as the other aquatic mammals. So we can be at neutral boyancy with o2 in the lungs.

And we don't have nearly as much hemoglobin and myoglobin. But we can still compete with sea otters (they can go 10 minutes under water - not so much more than us actually).
Mammals do not exhale to achieve neutral buoyancy, because not all mammals exhale. Dolphins and sea otters inhale. The choice of exhaling is made to avoid decompression sickness, which is why only the VERY deep mammals do it (whales and some seals). Even seals will sometimes inhale on shallow dives, but exhale for deep dives.

The myoglobin concentration figures Gerard posted are the average, much as you might quote the VO2 max average for the human race. But, there are people who have VO2 max scores of over 100 mlO2/min. Likewise, with proper training myoglobin can be dramatically increased. For example, baby emperor penguins are not born with high myoglobin, in fact upon birth their myoglobin is not much more than a human. But after just 2 years of diving every day, their myoglobin reaches 70-80mg/g, more than ten times what they are born with.

For more comparisons of inhaling vs. exhaling, read the many threads on FRC diving. This was discussed already at length.

Eric Fattah
BC, Canada
Thank you for correcting me; I had read that exhalation was done by aquatic mammals to reduce boyancy so at least I'm not the source of the misinformation!

Also, can anyone please spell out FRC? I don't know what it means yet.
Regarding the rise of myoglobin concentration in emperor penguins of more than 10 times after just 2 years of diving mentioned by Eric Fattah it would be very interesting to know the following:

1 If the emperor penguin cannot dive the first 2 years does his myoglobin concentration still rise that much or does it not rise?
2 How do emperor penguins start their diving? How do they train?

Could freedivers learn anything from this (or other animals) regarding training methods? Maybe studying the animals could improve our training methods for freediving.

Does anyone have a clue?
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