Joshua Chaffee
Joshua Chaffee

Oct 20. 3 mins


When you first begin the journey of life that is a newly found freediving obsession, you might quickly hit a massive wall. You can get through a minute, maybe two, underwater, but quickly your body starts begging you for air. Your body begins to contract violently and uncomfortably. If you are deep underwater, they can strike a sense of panic into beginner freedivers.

What is going on?

Diaphragm contractions.

These contractions happen as a response to high levels of CO2. They can be intense, and for some people, begin very early in a breath-hold. Diaphragm contractions could be what’s holding you back from reaching the full potential of your breath-hold. If you give up and rise to the surface to take a deep breath of that delicious fresh air after suffering through merely seconds of contractions, you are robbing yourself of a third or more of your potential time under the surface.

So what can you do?

Surprisingly, there are quite a few tips for enduring diaphragm contractions and even learning to enjoy them to a degree! If you apply these tips and soak in the extra bit of knowledge, you can find yourself enjoying your dives more and staying under for longer.

Understanding the Mammalian Dive Reflex

When mammals are submerged into water, they experience something called the mammalian dive reflex. This reflex allows all mammals, including humans, to hold their breath for longer and avoid drowning. There are many aspects of the dive reflex. However, the two main changes in the circulatory system are as follows:

  • Bradycardia— The heart rate begins to slow rather quickly after the face comes into contact with cool water. The average human heart rates slow anywhere from 10-30% but can slow more than 50% in trained freedivers.
  • Blood shift— Blood is redistributed throughout the body from the extremities such as arms and legs into more vital areas such as the head and chest cavity. Peripheral vasoconstriction will occur to assist this process meaning that certain veins become constricted to deny blood to certain areas, preserving it for more important things. In deep dives, blood plasma and water are allowed to pass through organs and into the chest cavity to protect it from the increase of pressure.
  • Splenic contractions — The spleen acts as a reservoir of oxygenated blood for the body. So, as your dive goes on, the spleen slowly contracts, releasing its storehouse of fresh oxygen into your body. (This is especially noticeable in mammals such as deep-diving seals as well as ancient freediving cultures such as the Bajau people, who have significantly larger spleens due to hundreds of years of apnea, natural selection, and the role of epigenetics.)

As your body spends each minute underwater without fresh air, it dives not only in depth but also into its own dive reflex.

One aspect of this dive reflex is the uncomfortable diaphragmatic contractions that begin for freedivers just under the 2-minute mark. One thing that makes them harder to endure is that these contractions are seen as an enemy who is attacking your body and forcing you to come up for air.

That is frankly not the case.

When these contractions begin, they allow the diver to know where they are in their breath-hold and how much oxygen they have left. An expert freediver understands that once these contractions begin, they are nothing more than a notification that they have “so much” time left, depending on their abilities.

Some estimate, using “the rule of thirds,” that once these contractions begin and you are struggling with them, that you still have about a third of your total dive time left with that breath-hold. (It should be noted, however, that these contractions begin for everyone at a different place in their dive. For some divers who can hold their breath for over 5 minutes, their diaphragmatic contractions still start at under two minutes.)

More than just letting you know how much oxygen you have left, the contractions also help your body preserve oxygen and protect you from a blackout. They increase the partial alveolar pressure of oxygen, increasing your blood oxygen level using the air still in your lungs. They also increase the partial arterial pressure which better oxygenates the brain with the oxygen that is left.

So what does all this mean for you?

It means that you should stop looking at diving contractions as your enemy and start to view them as your extremely helpful friend. Imagine each contraction as a pump of oxygen to your brain. This might help you cope with the uncomfortable contractions better psychologically.

Pushing Through the Contractions

As mentioned earlier, beginner freedivers tend to give up quickly when faced with diaphragm contractions. This is due to their low tolerance for CO2.

As you dive, you will more easily be able to simply ignore your contractions. This is because of two reasons:

  1. Through training, practice, and bodily adaptation, the contractions will come later.
  2. The pain and discomfort you feel from the contractions will be easier to bare. Think ahead a few years. After thousands of dives, when you begin to feel the contractions, you will think: “Oh, those same old contractions. I’m used to those. I’ll just keep swimming.”

One thing that might help you accept the fact that the beginning of contractions doesn’t mean that you are dangerously low on oxygen is to simply measure your oxygen levels during practice. You might find that your O2 saturation is still well above 80% when they begin. Levels of oxygen saturation aren’t typically considered alarming until they are below 65% and blackouts typically occur near 55% O2 saturation. (Remember that these saturation levels will not be exact for each person, they are only stated as a generality.)

Dealing with contractions should be accepted as a simple truth of part of the battle of freediving. Everyone deals with them and experiences them differently. Some freedivers make a game out of it during practice to see how many contractions they can endure before taking a breath. Try counting each one during a static breath-hold and see if you can beat your previous record.

One of the biggest factors behind enduring diaphragm contractions while freediving is your mental attitude. If you are stressed or panicking, you won’t be successful. Remember to think of your “breathe up” times more as “rest up” times. Always remain calm, and remember to never hyperventilate to delay contractions. You can further increase your CO2 tolerance by practicing your O2 and CO2 tables. This is briefly outlined in this article, as well as other tips on how to increase your overall breath-hold.

However you choose to cope, whether you dive with CMAS or AIDA, remember that having a proper understanding as well as the right mental outlook will go a long way in helping you to endure those pesky contractions.


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