Don't freedivers have to do some predive breathing exercises to rid the co from their system?
How long is your freedive with zero preparation and empty lungs?
Some people seem to be following a logic that I think many scuba divers follow. Namely, that if a freediver can dive to X feet or do a static breath hold of y minutes, then they should be able to ascend (with scuba gear) from a depth of 2X and swim up for y minutes.
This assumption is completely unrealistic and although it sounds reasonable at first glance, it is not valid. I think this/these assumptions are generated primarily because people have very little or no experience in freediving, static breathhold and even practicing open water CESA’s.
The first point that needs to be made is that a freediver takes a loooong time to prepare for a long dive. They must rest and ensure that all lactic acid has been removed from prior activity, they also generally remain motionless, they also concentrate on slowing the heart rate and calming down and they also go through a regiment of pre-dive breathing cycle which supports these physiological and psychological adaptations.
In short, they are super rested, super calm, very relaxed and if they are at all good at the activity, their heart rate has dropped a good bit. Many of the divers even try to manipulate the activity in the brain, since thinking actually burns a good bit of oxygen. When all that is in order, they begin their dive. They have a very good idea of the dive plan (or static time) they have spotters who will observe them during all (or the most critical portions of the dive) and they have a considerable awareness of time, depth distance etc. And their heart rate will continue to go down even further during the dive.
To compare a freediver who is in this state to a scuba diver who has probably been actively swimming (and has an elevated metabolic rate), and then suddenly discovers that he has no air, and no other means to secure air and then realizes that they need to swim up wearing all this drag inducing scuba gear and if they don’t “make it” they will die. Who in their right mind looks at the performance of a freediver (doing a PB) and thinks it is applicable (or equates) to a scuba diver who is most likely on the verge of panic?
To further this discussion, the maximum static breath hold of a freediver is measured while they float motionless on the surface of the water, while they are in touch contact with a qualified safety person who is communicating with them by tactile signals, verbal commands and also keeping track of time. The static breathhold of a person is far, far longer than their ability to preform apnea while actively swimming – even when calm and rested and prepared.. So even for an accomplished freediver, their static time may be, (somewhat of a guess because I personally don’t do this stuff) approaching double of their swimming apnea times.
So to make a long story short, a three minute static breathhold (personal best record) does not equate to 3 minutes of swimming in scuba gear.
However, a trained freediver has built up a tolerance for increased carbon dioxide and possibly even for low oxygen. This acclimation may not make them less likely to lose consciousness for a particular dive, but it does allow them to continue to function without panic or by generating self induced stress that is undesirable. In other words, they MAY be able to stay calm (which provides a huge advantage) but the advantage probably does not extend a whole lot past that point. It certainly does not automatically give them the ability to actively swim for three minutes when beginning with elevated carbon dioxide levels or a load of lactic acid that is also screaming for oxygen.
And one MORE factor that may be considerably different. A freediver starts with their lungs completely filled to the max at the start of a dive (some advanced divers even go through a dangerous process of overfilling their lungs ("packing") before a deep dive). A scuba diver COULD discover he has no air supply AFTER he has exhaled.
The impact of having empty lungs at the start of apnea should not be underestimated; the negative effect is huge. Even if there is sufficient oxygen in the tissues, the rapid rise in carbon dioxide in the lungs (because they are effectively empty) is extremely uncomfortable, can easily induce panic and can even cause impairment of the ability to function.
.
