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Underwater Photography, Instagram posts and record attempts seem to be the main trend for Freedivers nowadays, let’s take a step back and look deeper into breath holding itself. The basics, triggers and secrets behind the best freedivers in the world (Hint: it’s not the Sperm whale) who can dive to almost 3 Kilometers deep and stay underwater for 1.5 hours.
MDR and Apnea
Freedivers are aware that the human body reacts under certain actions like facial immersion, holding our breath-hypercapnia (high-co2 levels) and pressure. Triggering the very famous Mammalian Diving Response. This series of adaptations happen to all vertebrates, on different scales and efficiency. These series of adaptations include Bradycardia (slowing heart-beat), Peripheral Vasoconstriction (blood flow increasing in vital organs and decreasing in limbs), Immersion Diuresis, Blood Shift and the Spleen effect, pointing out this organ under pressure releases stored red blood cells into the blood. Enhancing our breath-hold.
The presence of Hemoglobin, a protein in the red blood cells produced by the bone marrow, which gives the red color to blood, regulates pH and its in charge of oxygen delivery from the respiratory system to the body tissue and back. On average, a healthy person carries 12 to 20 grams of hemoglobin in every 100ml of blood.*
There is another existing protein in the blood, that is key for the performance of all breath-holders in our planet: Myoglobin
So, what is Myoglobin?
Its a protein which is mostly found in the skeletal muscle and heart tissue, it contains iron (like hemoglobin) and its main job is oxygen storage.
Its also the one that gives diving animals a dark color in the meat (since myoglobin is located in the muscles).*
Presence and effects of Myoglobin in Humans and Animals
Some mammals evolve in different environments, and the ones that spend all their lifetime in the water, have been adapting for hundreds of years to this environment and their skills to be able to survive on it, too.
Many studies suggest that the longer the species have been performing diving activities, the stronger their adaptation and skills.*
It is natural to understand that marine mammals who spend more than 70% of their time diving, require a lot of oxygen storage in their muscles, and this can only be achieved by higher levels of myoglobin.
The main issue for scientists was understanding how, since proteins “cancel” their efficiency due to particles sticking together when there’s a high concentration of them, how could a marine mammal store so much oxygen in their bodies and perform such long and deep dives?
Recent studies made by the University in Liverpool state that the electrical charge in the myoglobin surface increases in marine mammals, causing electro-repulsion, preventing proteins from sticking to each other and allowing a much higher concentration of oxygen- storing Myoglobin in the marine mammal’s muscles. Since they have an ancient story of diving activities, this effect allows them to store more oxygen and enhance their deeper and longer dives. This is one of the main reasons why humans cannot perform such dives, in our case the myoglobin levels are much less, and it might not behave the same way as these deep divers.*
Humans have almost ten times lower (more precisely 9.3 times lower) myoglobin content in muscles (8 ml/kg) than sperm whales (74.7 ml/kg), and 8.4 times lower than seals (69.3 ml/kg). The ratio is 10-30 times comparing diving and terrestrial mammals.
An interesting fact is that a particular penguin (Emperor) are born with a similar amount of Myoglobin levels as humans (8mg/kg), but after diving activities throughout the years, their levels increase as much as (50-75mg/kg).
Other adaptations of Aquatic Mammals
The Mammals that perform long and deep dives are also the ones with the biggest oxygen stores. But that’s not all, marine mammals count with several more adaptation for their needs. For example, their blood volume is way higher, around 3 times, meaning there is more red blood cells, hemo-proteins and of course oxygen available.
Some marine mammals like Dolphins and seals, have developed elastic aortic bulbs and plexus, who are thought to work maintaining arterial pressure during bradycardia in the dives.
Hypoxia is another factor that aquatic animals have mastered, their brains produce more levels of neuroglobin and cytoglobin, this molecules are thought be recruited to fight hypoxia in the brain during dives.*
It is known that the approach of the dives plays a big role on the efficiency and duration of marine mammal dives, the more mature the more efficient, their training and duration of dives increases, also their physiological adaptations enhance.
Factors like gliding, surface intervals and speed of the dives, directly affect their performance (just like us).*
Deepest Freedivers in the World
It is popular knowledge to believe the Sperm Whale is the deepest freediver in the world, diving down to (7,382ft – 2,250m) but it’s actually not, the scientists of the Scripps Institution of Oceanography tracked a Cuvier’s Beaked Whale (Ziphius Cavirostris), which is a small sized whale commonly sighted all around the world, they mostly feed on deep squid and fish.
Scientist were able to register a 9,816ft – 2,992m deep dive, and spent two hours and 17 minutes underneath the surface, being the deepest and longest dive ever done by a Marine Mammal.*
Through training and adaptation, the human body is known to develop unbelievable performances regarding apnea and deep diving, achieving self propelled dives down to 130m which compared to other marine mammals like river otters, humans are not the worse marine mammals at performing different kinds of breath-holding activities.
There are human limits regarding freediving as a sport/discipline, which are still being explored and pushed as time pass by, but the series of adaptations seen in our fellow marine mammals are beyond human expectation and performance.
Bibliography – Sources