- Constant Ballast: You dive as deep as you can and swim your way back to the surface. The weight belt (if used) has to be brought back to the surface with you
- Variable Ballast: A maximum of 30Kg of weights can be used to help speed up the descent. These are then removed before finning your way back to the surface. Obviously people go deeper this way than in constant ballast because they don’t use any energy to go down
- No Limits: You can use as much weight as you wish to assist you in the descent, and you can use an inflated balloon to bring you back to the surface. Think of this category as an ‘elevator’ taking you deep down and then bringing you back to the surface
- Dynamic Apnea: You try to swim underwater for the maximum distance you can. Two variations exist: with fins or without
- Static Apnea: Simply getting under water and holding your breath for as long as you can
These catagories are all subdivided into mens’ and womens’.
Physiology of Freediving
As a Freediver (or a Scuba diver) makes their descent into the sea, the pressure on the outside of the eardrum increases and as a result the eardrum is pushed toward the inside (which can result in pain). The diver uses what is known as an ‘ear pressure equalisation’. This lets air into the middle ear in order to ‘equalise’ the pressure at both sides of the eardrum. A couple of techniques are available but the most common one involves pinching the nose while trying to blow air through it. This forces air to the middle ear through the Eustachian tube.
In ancient greece sponge divers used to ‘break’ their ear drums when they were young by diving in deep waters without equalizing (although they knew the technique). By doing so, they wouldn’t need to equalise the pressure in their ears anymore.
Imagine the following experiment. A closed plastic container filled with air is slowly submerged in water. As water pressure increases around it, the container will eventually be crushed. Now think of our lungs as being the plastic container mentioned above.
When Scuba diving your lungs are not crushed because the air you breathe is at the same pressure as the surrounding water. This equalises the water pressure. What about when Freediving? Clearly there is no extra air going into our lungs to equalize the pressures. Indeed the lungs get a squeezed. For years, Doctors to believed that if Freedivers went deeper than a certain depth, their lungs would ‘crush’ and death would occur. Freediving champions proved them wrong.
In fact those divers went significantly deeper than the maximum doctors predicted. After further experiments and observations, it was found that a ‘blood shift’ mechanism is present in the human body. As we go deeper in water, blood shifts from other parts of the body and begins to flood our lungs to equalise the outside water pressure. Our heart rate slows down and blood pressure increases. This is why our lungs don’t crush in on themselves as foctors used to believe. The same “blood shift” mechanism is present in all sea mammals.
When you hold your breath or submerge your face in cold water the mamalian dive reflex is engaged. This slows down the heart rate extending the time that you can hold your breath.
The equipment used in freediving is very similar to that used for scuba diving. There are a few differences because a freediver has only one breath, which must be used as efficiently as possible.
As you descend while scuba diving the pressure increases and anything which can compress is compressed. This includes the air in your mask. This is known as a ‘mask squeeze’. To equalise the pressure you need to blow some air out of your nose into the mask. A freediver must do the same thing.
So what is the difference? The amount of air you need to blow in your mask in order to equalise the water pressure, is proportional to the volume of air in the mask. This is why freedivers use low volume mask. A normal mask needs more air to be blown in it (air that comes from the lungs and not from an air tank).
As a freediver ascends to the surface, the air in the mask expands. Instead of allowing that air escape out of the mask a freediver breathes it back in through their nose.
Freedivers use wetsuits that are specifically designed for freediving (which tend to be thinner than scuba diving wetsuits). This means fewer weights are needed to descend. It also means you become positively buouyant at a deeper depth (making freediving safer). Thinner wetsuits are also more hydrodynamic, so you use less energy while swimming. Obvioulsy there are trade-offs, namely warmth. A thinner wetsuit has less insulation than a thicker one. However while freediving, as you are moving more than while scuba diving, your body produces more heat and so a thinner wetsuit all that is needed.
Freedivers tend to use elastic weight belts. As you descend, the air in your lungs is compressed and as a consequence your stomach moves in. This means that a fixed wieght belt (that was tight at the surface) will become loose as you descend. This is why elastic belts are used. As your body compresses the belt will remain tight.
This is the area where the difference between scuba diving and freediving equipment is most noticeable. Freediving fins are a lot longer and stiffer than scuba diving fins. This makes them a lot harder to move underwater. They require more energy to bend them, but they produce more force when they return to their original position. It is this ‘snap’ that gives you the thrust needed to move efficiently underwater.
Dangers of Freediving
Every sport has a few rules that should be followed. For some sports it’s a mater of fair play, for others it’s a mater of safety. No one gets hurt if you touch the ball with your hands in a football game, but you might get in serious trouble if you miss your decompression stops in scuba diving. Freediving is one of those sports where you might get in serious trouble if you push things too far. The single biggest danger in Freediving is hypoxia.
As freediver descends the air in their lungs gets pressurised. This causes a false sense of increased oxygen level in the lungs (increased O2 partial pressure). If the freediver pushes themself too far and stays down too long, then on ascent the decreased oxygen level (decreased O2 partial pressure) might fall below the critical value and as a result the diver suffers from hypoxia. Hypoxia can hit you any time the partial pressure of oxygen drops below the critical point.
Hypoxia is also known as ‘shallow water blackout’ because most of the time it happens in shallow water. A milder form of hypoxia is called ‘samba’. This is when a Freediver makes it to the surface without blacking out but their body goes into convulsions. The name comes from the fact that the freediver is shaking as if they are dancing the famous dance. One thing to keep in mind is the fact that the urge to breathe is triggered an increased amount or carbon dioxide in our lungs, not the need for oxygen. Some people find that by hyperventilating before a dive you are able to hold your breath for longer. This however is not the case. By hyperventilating the CO2 levels in the lungs are reduced so much that the need to breath is almost completely removed. This means that hypoxia can hit without any warning.
Remember, never hyperventilate and never freedive alone.
For those who are interested in freediving, finding their limits and pushing them further, proper training is essential. Not just physical training. Freediving is as much a mental sport as a physical one.
Part of physical training involves training in the pool. Make sure you are with someone you knows what to do if something goes wrong. In the pool you can practice dynamic apnea and static apnea. There are two ways to do this:
- Hold your breathing interval constant and gradually increase the distance you swim or length of time you hold your breath for
- Decrease the breathing interval, while keeping the time or distance constant
This part of training is very important. You need to be relaxed. Being relaxed during a dive helps you slow down your heart and minimize oxygen consumption. You must enter a hypnotic trance/state. The ability to enter such a state is very useful in freediving (and other sports).
Training With the Club
Freediving courses are run on a one-off basis, usually once a year by inviting external instructors. Provided you have an AIDA 1* qualification (which can be obtained through attending the course) you can train during our normal training sessions with a buddy of similar qualification. Contact the Extended Training Officer for more information.