[alix.leclerc]

Discussion
Although the results above show that human freedivers have much in common with marine mammals, we cannot compete with the other physiological adaptations that allow marine mammals to remain underwater for so long, or dive so deep. Our bodies are not designed for a life underwater; we are poor users of oxygen, absorbing only 17% of the oxygen in our lungs where as marine mammals can absorb up to 85%. We are not very streamlined or efficient swimmers, we suffer cramps whereas marine mammals do not. Our major source of oxygen during a dive is from our lungs which lead to problems of partial pressures and narcosis whereas marine mammals store over 80% of the oxygen in their muscles and blood. Without a thick layer of blubber we cannot protect ourselves from the cold and our bodies cannot tolerate hypertensive blood pressure and other problems linked to pressure at depths. In short, we lack the physical characteristics which allow marine mammals to comfortably remain underwater.

Conclusion
From the extensive studies on the diving reflex in human freedivers, some of which are mentioned in this essay, it is clear that all of the main characteristics of the diving reflex in marine mammals are also found in human freedivers, although these responses may not be developed enough to allow us to dive to the same depths or for the same length of time as some marine mammals. Whilst bradycardia can be as effective in humans as marine mammals, with peripheral vasoconstriction and blood shift becoming more accentuated with training, our other physiological differences cannot allow us to achieve the same level of diving as Pinnipeds, cetaceans or sirenia, especially without the aid of equipment such as wetsuits and diving sleds. However, divers around the world have continued to push the boundaries of diving and science, proving that the human body is far more adaptable and able to function in situations than were previously thought possible. We have yet to discover the full extent of our diving reflex, especially within the psychological aspect, and there may still be many responses we have yet to discover. With more time, more research, and more dedicated freedivers, we may discover far more about our potential as breath-hold divers, how developed our diving response can become, and maybe identify the limits of our physiological capabilities.

I said it was long!