Freediving & Physiology

Recognition of freediving has grown as it has become a competitive sport and gained popularity among spearfishermen. In competitive freediving, divers compete to dive to the deepest possible depth on one breath of air. There are many disciplines of competitive freediving that affect oxygen and energy consumption including the use of fins, weights, and devices to assist divers down. No matter the discipline, the diver rarely exceeds a 1 m/s descent because the diver must have time to equalize middle ear pressure (Giunta, et. al., 2019). This can be done by pinching your nose and pressurizing the Eustachian tube as you would do to pop your ears on an airplane.

To perform a static breath-hold, a person will float face down in a pool, not moving for as long as possible. Generally, a diver is able to perform a dive using flippers for half the time of their maximum static breath-hold. The world record static breath-hold exceeds 11 minutes. To do this, divers must accomplish a few things physiologically. The first way is to train the muscles that control respiration. Using breathing exercises, people learn how to breathe using their diaphragm, intercostal, and shoulder muscles to maximize lung capacity. The divers utilize another breathing technique that maximizes blood oxygen saturation right before breath-hold. The diver must focus on relaxing all the muscles and thoughts before and during the breath-hold so that the body goes into a parasympathetic state to conserve oxygen.

The last thing a diver will do before a breath-hold is hyperventilate. Hyperventilating allows the diver to exhale excess CO2. When CO2 levels are low, chemoreceptors in the brain signal an urge to breathe (Albert & Craig, 1961). Hyperventilation can be very dangerous if not done properly causing divers to not recognize and reach hypoxic states that lead to unconsciousness and loss of motor control. Covington, et. al. (2019) looked at a new technique of freediving that utilizes oxygen-enriched gasses before, during, or after a free dive. This technique is called technical freediving and has resulted in static breath-holds exceeding 20 minutes. This technique combined with hyperventilation was shown to significantly decrease PN2 and PCO2 while it significantly increased PO2. Technical freediving has been shown to reduce risk of decompression sickness but increase risk of oxygen toxicity. This raises the concern of which method of diving should be considered safer and if there should be more research into long term physiological effects of freediving.

 

References:

 

Albert, B., & Craig, J. R. (1961). Causes of loss of consciousness during underwater

    swimming. Journal of Applied Physiology, 16(4), 583–586.

    https://doi.org/10.1152/jappl.1961.16.4.583

 

Covington, D., Lee, RH., Toffel, S., Bursian, A., Krack, K., and Giordano, C. (2019)

    "Technical Freediving: An Emerging Breath Hold Diving Technique," Journal of

    Human Performance in Extreme Environments: Vol. 15 : Iss. 1 , Article 3. DOI:

    10.7771/23272937.1122

 

Giunta, AAM., Lerberati, L., Pellegrino, C., Ricci, G., Rizzo, S. (2019) Eustachian tube

    balloon dilation in treatment of equalization problems of freediving spearfishermen.

    Diving and Hyperbaric Medicine. 49(1): 9-15. Doi: 10.28920/dhm49.1.9-15