Freediving/Freedive Safety

What Actually Happens Deep Down Under

For most of us, it’s human nature to always strive towards our best, regardless of what we’re working on (unless it involves making our boss – and not us – even wealthier. And even then we’ll still make the effort, even if it’s merely in the interests of personal satisfaction of a job really well done). It follows then, that as spearos (whether professional, provincial, rookie or social) we all want to increase our free-diving capabilities, continuously pushing our own boundaries to achieve that extra edge.

The current world record (in accordance with AIDA International) is held by Stephane Mifsu from France who managed a breath hold of 11 minutes 35 seconds in a static submersed position in 2009. In 2007, Herbert Nitsch of Greece dived down to a depth of 214m in the no-limit category of the sport.

One can’t help but wonder to oneself, how is this humanly possible? Although as spearos we do not need to dive to such depths or increase our breath-hold ability to such extremes (although an additional 5minutes on my down time would be fantastic!), the physiological changes and procedures that occur within the human body are much the same in all individuals.

The body is a very clever machine, which often functions in certain ways and manners that we may not even think about initiating or implementing. The body will always prioritise its survival over any act we may instruct it to do.

When any air breathing vertebrate performs a breath-hold dive, the same physiological procedures occur within the body. With this said, in breath-hold diving, the body senses a lack of oxygen and responds by reducing the blood flow to the non-essential parts of the body such as uninvolved muscles, splanchnic, viscera, and skin. This occurs in conjunction with an initial rise in blood pressure and a reduced heart rate resulting in less blood being pumped-out by the heart (cardiac output) as per normal.

In a study conducted on breath-hold divers who were particularly responsive to conditions of restricted oxygen supply, it was noted that peripheral circulatory resistance (the reduction of blood to the non-vital parts of the body) increased up to 5 times accompanied by large decrease in heart rate and blood being pumped by the heart. 2,3,4 The blood and lung oxygen stores are reserved for the functioning of vital organs i.e.: Brain and Heart, as the body ensures its survival.

The most amazing muscle of the human body, the heart, is made up of myocardial tissue (heart muscle) with its rhythmic and contractile components controlled by the medulla in the brain. The medulla transmits signals to the heart via the autonomic nervous system, made up of the sympathetic and parasympathetic nervous systems.

The stimulation of the sympathetic nervous system results in a severe increase in heart rate, which is necessary for when we need to swim out through big surf on a shore dive, or to fin out the path of a bullet-proof Zambi.

Stimulation of the parasympathetic nervous system results in a reduced heart rate, something which we tap into when we attempting to perform a decent down-time. Great control through relaxation and breathing techniques has a large influence on both systems, thus we attempt (subconsciously) to stimulate our parasympathetic nervous system and thus these extreme dives begin to become more realistic.

Further studies have been conducted in Hemoglobin concentrations and Haematocrit within the blood stream between non-divers, breath-hold divers, and elite divers. Hemoglobin is a component of our red blood cells, which oxygen binds to for oxygen transportation in the blood stream. Red blood cells are continuously being produced at the same rate which they die, as they have a lifespan of approximately 4 months. Thus if there were to be an increase in hemoglobin concentration or total hemoglobin mass there consequently would be an increase of oxygen availability in the blood stream, thus allowing for possible prolonged functioning on breath-hold dives.5, 6, 7, 8, 9, 10 Although this theory has not yet been proven as there has been conflicting evidence with regards to hemoglobin levels in different studies, further studies and investigations should be conducted in the regard.

One can only admire the functioning of the human body, and the subconscious physiological changes and adaptions that take place in response to various situations. Perhaps then, extreme breath-hold dives (as achieved by Stephane Mifsu and Herbert Nitsch) may be the result of personal control of these various mechanisms?

Could we tap into our bodies’ subconscious decision making process, and improve our free-diving capabilities? Possibly… and the prospects are very exciting. But that’s a discussion for the next issue of USM.

For more information on the effects of freediving on the human body, you can email Carl and he will be happy to answer any questions:

1. http://www.aidainternational. 

2. Ferrigno M, Ferretti G, Ellis A, Warkander D, Costa M, Cerretelli P, Lundgren CE. Cardiovascular changes during deep breath-hold dives in a pressure chamber. J Appl Physiol 83: 1282–1290, 1997

3. Lindholm P. Severe Hypoxemia During Apnea in Humans: Influence of Cardiovascular Responses (Thesis). Stockholm, Sweden: Karolinska Institutet, 2002

4. Lindholm P, Nordh J, Linnarsson D. Role of hypoxemia for the cardiovascular responses to apnea during exercise. Am J Physiol Regul Integr Comp Physiol 283: R1227–R1235, 2002

5. Bakovic D, Valic Z, Eterovic D, Vukovic I, Obad A, Marinovic-Terzic I, Dujic Z. Spleen volume and blood flow response to repeated breath-hold apneas. J Appl Physiol 95: 1460–1466, 2003

6. Espersen K, Frandsen H, Lorentzen T, Kanstrup IL, Christensen. The human spleen as an erythrocyte reservoir in diving- related interventions. J Appl Physiol 92: 2071–2079, 2002.

7. Hurford WE, Hong SK, Park YS, Ahn DW, Shiraki K, Mohri M, Zapol WM. Splenic contraction during breath-hold diving in the Korean ama. J Appl Physiol 69: 932–936, 1990.

8. Schagatay E, Andersson JP, Hallen M, Palsson B. Selected contribution: role of spleen emptying in prolonging apneas in humans. J Appl Physiol 90: 1623–1629; discussion 1606., 2001.

9. de Bruijn R, Richardson M, Haughey H, Holmberg HC, Björklund G, Schagatay E. Hemoglobin levels in elite divers, elite skiers and untrained humans. In: 30th Annual Scientific Meeting of The European Underwater and Baromedical Society on Diving and Hyperbaric Medicine. Ajaccio, France: National Research Establishment.

10. de Bruijn R, Richardson M, Schagatay E. Increased erythropoietin concentration after repeated apneas in humans. Eur J Appl Physiol 102: 609–613, 2008.


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