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The science of freediving
text: Sebastian Naslund
New thesis on freediving by P. Lindholm (20021005)
The dissertation - breathhold test - seven sambas

For me freediving is a way to explore my own body – So when I, at the same time as I started with freediving in 2000, was offered to take part in a ”breathhold study”, I was more than happy to put my body a the service of science.
The studies were conducted by swedish Peter Lindholm at "Karolinska Institutet" in Stockholm pursuing his PhD in medical science.
I was a volunteer in different experiments during two years and it has been an opportunity to to learn about and measure my bodys biological reactions during apnea.
Out of my point of view as a volunteer and a freediver I have learnt things that actually speeded up my development as a freediver.

In fact it has been known for over a century that our pulse drops during breathold diving. Later it was discovered that this also happens in seadiving mamals.
Was there a link? How could it be explained?

Today it is common knowledge that there is a diving response that consists of more than a lowered pulse. Why and what this really means for the person holding their breath is not fully explained yet. The romantic explanation to why can be explained by the antropologists aquatic ape theory.
What the diving reflex REALLY does for a freediver was one of Lindholms ambitions to find out. To find if there was a biological significance. He also wanted to find out if the diving reflex varied inbetween persons, therefore not only fredivers were tested but also "ordinary people".
Diving response See *below
*Bradycardia Drop in pulse
*Anaerobic metabolism Cells ability to function without oxygen
*Vasoconstriction Bloodvessels shrink. Bloodstream directed away from limbs for the benefit of heart, lungs and brain.
*Splenic contraction Releasing red blood cells carrying oxygen
*CO2 tolerance After repeated breatholds
*Higher blood pressure To "compensate" lower heart rate and less stroke volume.
*Less stroke volume in heart To "compensate" vasoconstriction.
Blood shift Blood fills up bloodvessels in the lung and reduces residual volume.
Blood shunt Term wrongfully used for vasoconstriction
Residual volume RV Whats left in the lungs after FULLY breathing out
Vital capacity VC the maximal amount of air you can exhale in one breath
Total lung capacity TLC What your lungs contain when taking a full breath
Lungpacking/ carp breathing Swollowing air into the lungs
Hypoxia Lack of oxygen
Lack of oxygen in the blood.
hypercapnia The presence in the blood of an abnormally high concentration of carbon dioxide.
A condition in which there is an abnormally low concentration of carbon dioxide in the blood. This may be caused by hyperventilation
Hyperventilation Higher then normal intervals of breathing (cycle) – lowers carbon dioxide (below usuall 4.5%)
Stroke volume Amount of blood in each heart stroke
MAP Mean arterial pressure
ECG Measures the heart rate and its function.
02 narcossis Oxygen narcossis due to pressure at depth.
N2 narcossis Nitrogen narcossis due to pressure at depth.
CO2 narcossis Carbon dioxide narcossis due to pressure at depth.

...involved breathhold at static position and also while cycling on an ergometer cycle. At one point this cycle was immersed into a water tank. Pulse was also measured during actual diving down to 43 meter. At this time a submersible EKG was used. Bloodpressure, heart pump volume, oxygen levels, RV, VC and other things were measured. Other tests involved measuring the oxygen levels right at the heart. This was done by putting a tiny plastic tube up the vein from the armpit to the heart. (oxygen levels in the blood from the heart differs from the "used" blood coming back from the muscles). The tests also involved breathing different gases before breathold, sometimes raising the carbondioxide levels in the blood to quite disturbing levels and of course moving towards the edge of hypoxia.

- The more bradycardia the more oxygen conserved
- The more vasoconstriction the more bradycardia
- Hypoxemia stimulates bradycardia (but is not the principal cause)
- Heart rates during competitions were higher than during training

This might seem to be common knowledge, at least among us who train breathhold diving - but actually proving it scientificly is an other matter.

More about Peter Lindholms thesis can be read at It is also possible to order his thesis in full (in english). As all scientific scripts its quite uncomprehensible for the common man.
More scientific links on freediving under LINKS.

Future tests will involve MR camera (3D photo of the chest) during different apneic exercises. Gene-tests of freedivers. And some stuff Lindholm wants to keep secret.

Peter Lindholm - do have his heart in freediving. Having his peronal best somewhere close to 40. He also have experienced samba at a competition. He has attended courses with Pelizzari and Kirk Krack.

To the left - his car.

Senast uppdaterad on August 4, 2002 by ©Webvideo.
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