Spitting blood after freediving: squeezes and squeeze-like symptoms

You might have come up from a dive and coughed up some foamy pink mucus, or some phlegm with blotches of blood in it. Chances are that you experienced a squeeze. We will discuss the causes for squeezes and squeeze like symptoms in this article. If at some point you were spitting blood after freediving and wondered what was going in, keep on reading.

As usual, remember that I am not a doctor. The symptom of spitting or coughing up blood is called hemoptysis and can have numerous (potentially life-threatening causes). If in doubt, see a doctor.

True squeezes

Squeezes happen when the negative pressure on the lungs or trachea is too much for the tissue to handle. Squeezes commonly do not occur unless you reach residual lung volume. Residual lung volume is reached between 25 and 45 meters for most divers, depending on how big the inhalation was and if the diver packed or not. A squeeze may occur at shallower depth if you have bad posture, or if you have heavy contractions.

Trachea squeeze

The trachea squeeze might be the most common squeeze type. The trachea is the least compliant to pressure changes. It is essentially a tube reinforced with cartilage rings. These cartilage rings don’t stretch very well and keep the trachea open, even if you would rather have it collapse. Blood vessels along the wall of the trachea can rupture if the negative pressure becomes too high.

Phlegm from the trachea looks white, transparent colourless, or transparent yellowish (opaque yellow or green if you have an infection), and will contain blotches or strings of blood if you have a squeezed trachea.

spitting blood after freediving
Find the trachea, lungs and alveoli here.

Lung squeeze

The lungs are soft spongy organs that stretch and compress better than the trachea, but unfortunately they can still get squeezed. If the lungs are subject to negative pressure, yellow fluid can start to leak into the lungs from the alveolar capillaries. Although this is not diagnostic of a squeeze, it does mean that you are descending to depths at which you may be at risk.

If the negative pressure increases, capillaries in the lungs may start to rupture, causing blood to fill the alveoli. This is called a lung squeeze.  If you have suffered a lung squeeze you will cough up pink foamy mucus.

What do you do after a squeeze?

There are no set guidelines for how to deal with squeezes. Most teaching organizations will state you need to be medically cleared for diving by a specialized doctor. Although I agree, my guess is that most divers do not follow this mandate.

Another recommendation that I have seen is as follows:

If your sputum (sputum = what you cough up) contains less than 50% blood, take one week off diving. If your sputum contains more than 50% blood, take two weeks off diving. If you only cough up blood, seek medical attention as soon as possible.

This is a more conservative approach:

If you see less than 25% of blood in your sputum, take one week off diving. If you see 25 – 50% of blood in your sputum, take two weeks off diving. Seek medical attention if:

  • You see more than 50% blood in the sputum
  • You cough up fresh blood more than 12 hours after the dive
  • Other symptoms such as pain or tightness in the chest are severe
  • Any symptoms persist for more than 5 days
  • SaO2 is <95% more than 15 minutes after the dive

Note that the symptoms will probably be gone within a day or two. This does not mean you can go back to diving again. The damaged tissue will likely still be weak and you should give it ample time to heal.

Protecting yourself against squeezes

  • Technique

To avoid getting squeezed, practice your technique at maximum 20 meters depth. Until you can do a dive with perfect posture (including the turn), do not dive deeper.

  • Stretching

Intercostal and diaphragm stretches will help increase the flexibility of the ribcage, and protect yourself against squeezes. In Pre-Dive Preparation, Sara Campbell teaches excellent stretching routines.

  • Gradual adaptation

Your body protects the trachea and lungs by blood shift, an effect of the diving reflex. Your adaptation to depth should be gradual to allow your body to get used to the depth and the required blood shift. In Holistic Freediving, Eric Fattah shares methods of training the dive reflex.

Not all squeezes are squeezes?

From April 2016 onwards, I started getting squeeze like symptoms on dives shallower than 25 m. These dives were well in my comfort zone, my average leisure dive was about 20 – 30 m. I would come up and cough up bloody sputum, indicative of a trachea squeeze. One time, the issue seemed to start 5 minutes after my last dive.

I took a week rest every time it happened and started more serious stretching of the lungs and trachea, to no avail. After I got back to diving, it was only a matter of time before the next ‘squeeze’.

It took me a while to figure out what was going on.

The ‘squeezes’ started after I moved to a busy intersection, with poor air quality. During that time, I had more colds, and often had an aggravated throat. I was more ‘phlegmy’ to start with. After I realized that the ‘squeezes’ started after I moved places, I bought a HEPA (high efficiency particulate absolute) filter and put it in the bedroom.

End of story.

Since I have started using a HEPA filter I have not once had squeeze like symptoms despite diving deeper, I’ve had better sleeps, and less colds. Starting your dive with an aggravated throat greatly increases the chances that you burst a blood vessel in the throat. Poor equalization technique probably increases the risk. Although the symptoms are the same as those of a trachea squeeze, these are not squeezes. They may occur simply when you clear your throat at the surface after a dive.

Immersion pulmonary edema

A phenomenon that results in similar symptoms (to those after squeezes) is called immersion pulmonary edema (IPE). This is a leakage of fluid from the bloodstream into the lungs. It has been reported in triathletes, swimmers, U.S. navy SEALs and scuba divers. You can read more about IPE on the website of DAN (Divers Alert Network). Although IPE may be somehow related to squeezes, the cause is likely different from negative pressure induced edemas.

Please share your experience in the comments.

Breathe up time: the key to relaxing dives

How long should your breathe up really be? When you surface from a dive, your body needs to replenish its oxygen stores and high energy phosphates. The body also needs to get rid of the excess CO2 and other waste products such as lactate. Once that is done, or perhaps at the same time, you need to start relaxing for the following dive. But how long does it take? A minute? Ten minutes? Let’s find out.

This article is not about decompression sickness, which I will cover in another article. 

Oxygenating the blood

For an average Joe with 70 kg body mass, 5 liters of blood and a heart stroke volume of 70 ml, the blood is pumped around completely in 71 strokes (5000 ml of blood divided by 70 ml = 71). Based on the assumptions that 1) his heart rate rises to about 110 immediately after a dive and drops after a minute, and 2) the lungs fully oxygenate all blood that passes by, he should have fully oxygenated blood within 39 seconds.

After 39 seconds, your blood is fully oxygenated.

If you have ever done 2 dives with only a 39 second breathe up in between, you know that this is not the full story. The body is not yet back to steady state within 39 seconds, so let’s continue exploring this topic.

High energy phosphates

You may have read my articles on muscle metabolism and muscle fiber. If you have, and you were not abysmally bored, you may remember the ‘high-energy phosphates’ or ATP-CP. If you did fall asleep on your keyboard while reading here is a one sentence recap: ‘High energy phosphates in muscles can provide energy for about 10-15 seconds of maximal muscle contraction and do so without costing O2 or producing CO2’. But how long does it take to replenish these high energy phosphates after a dive?

Up to 70% of CP is resynthesized in 15 seconds. If you are severely vasoconstricted because of cold or the dive reflex it may take somewhat longer. The remaining 30% will be resynthesized after roughly 2:45 minutes, so you need about 3 minutes in total to replenish high energy phosphates.

After 3 minutes, your high energy phosphates are replenished.

Excess CO2

And what about the stuff we need to get rid of after a dive? How long does it take to vent off all that excess CO2? Available data for the recovery of Steller sea lions suggest long recovery times (large variations between individuals are common). These recovery times are based on VCO2, the exhaled carbon dioxide after a dive.

For a dive of 3 minutes, VCO2 takes approximately 5:30 to recover, and for a dive of 2 minutes we can expect a 4-minute recovery time. The reason CO2 levels take a long time to return to normal is that CO2 is transported throughout the bodies tissues, and it takes time for the CO2 to make its way back into the bloodstream and to the lungs.

breathe up
As usual there is more data available of diving mammals than of humans. This is a grey seal.

Of course, we are not Steller sea lions. Steller sea lions are much larger and adults can weigh over 1000 kg (2200 lbs), and have lung volumes that are proportionally larger than those of humans. But does that mean that they lose CO2 faster or slower than us? My guess is that because of our size we lose CO2 at the same rate or perhaps somewhat faster than Steller sea lions, but I can’t prove it.

The release of CO2? Unknown, but likely less than 4 minutes for a 2-minute dive.


Now I did talk about lactate earlier. As it turns out it takes about an hour for lactate levels to return to normal after heavy exercise (or a dive during which you feel significant leg burn). This recovery time can be reduced to about 50 minutes if you go jog or go for an easy bike ride.

I wouldn’t wait for it if I were you. A better solution would be to not dive to exertion, so you will have a longer dive session. Lactate is only produced in significant quantities once your muscles become hypoxic. You can feel it as leg burn towards the end of your dives.

Lactate? Don’t wait for it…

In conclusion, if you want to make long and comfortable dives your breathe up should be at the very least 3 minutes, so that your high energy phosphates are fully recharged. Better still, take 4 minutes in between dives so that your CO2 levels are back to normal. Of course, during the breathe up, and especially the last 2 minutes you should try to be completely still.

And another method is to not overthink it and just do what feels right… But that would not make for very interesting articles. Let us know what your approach is below!

We’re giving the amazing 6-part Yoga For Freediving course away for free!

Woops you’re too late! This competition has ended & the winners have been notified.

In the final part of Yoga For Freediving, Sara Campbell teaches us how to prepare for dives. She teaches us how to do a 30 minute warm up specific for freediving. This includes spinal energizers and intercostal stretches and much more. Following the warmup are about 15 minutes of lung stretches. Because not everyone is at the same level, both the warmups and the lung stretches come in three varieties: beginner, intermediate and advanced.

In Pre-Dive Preparation, Sara gives you a modernization of the best of Kundalini Yoga, and of the freediving manuals that exist today. Better yet, she is right in front of you as she guides you through the practice.

True, you could probably think of your own stretching routine, and some of you might even stick to it. You may even have half a notebook full of the exercises that work for you. But when it comes to it… Do you tend cutting them short half way if you get distracted, or do you simply not make time for them? If nothing else, Sara keeps you honest.

The first time we used the Pre-Dive Preparation course for our… well, pre-dive preparation, we had 2 personal bests in one diving session. We are sold.

Yoga For Freediving by Sara Campbell
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To enter the competition, you simply need to leave a comment! Better still, subscribe to our e-mail list while you are at it. You are getting an easy shot at winning the full Yoga For Freediving course, worth $300, so don’t be shy. Winners will be selected on Wednesday September 13th and the Yoga For Freediving team will contact you after that.

Tell us your take on freedive preparation below for your chance to WIN the full Yoga For Freediving course.

The terribly wrong image of freediving

A shorter version of ‘the image of freediving’ originally appeared as a Freedive Wire newsletter.

It is a sport that only people with a death wish practice. A sport for adrenaline junkies that like to dance with death. A sport for athletes that do not mind putting their life on the line. This is the image of freediving. But is it correct?

Four out of ten of the results for ‘freediving risk’ on google:

image of freediving

On the web, a bit of danger, adrenaline, and risk sells. These articles will get many reads simply because of their title. But are they true?

People that do not freedive usually see freediving as a sport that attracts lunatics and adrenaline junkies that like nothing more than to put themselves in danger. Freedivers on the other hand, normally use words such as ‘peaceful’, ‘relaxing’, and ‘self-discovery’ to describe the sport. Spearfishers may talk about the thrill of catching a fish on breath hold, but also about the calmness of the underwater world.

This difference is important, because the way that the general public perceives freediving affects for example club insurance policies and where we are able to practice and dive. Why does the difference exist in the first place?

When freediving gets media attention, commonly somebody tries to break a record. Take for example Will Trubridge’s 102 m dive last year. The dive got attention from for example New Zealand Herald and BBC, and was well marketed by his sponsors, Steinlager, Suunto and others. Freediving underneath ice receives a disproportional amount of attention on social media.

Even though we now have strict safety protocols for record attempts, the focus of freediving in the media often lies on the risks of black out and drowning. Sometimes, freediving is described as ‘a dance with death’. I doubt that many divers that do these record attempts truly feel like they are dancing with death.

In fact, Guillaume Nery dived 10 meters deeper than he intended due to a bad mistake by the organizers (AIDA individual depth championship 2015). He stated afterwards ‘I felt like they were playing with my life’. That does not sound like a statement from someone who likes to dance with death. But hey, risk sells.

Despite the image of freediving, most of us do not actually care to dive very deep, to break records, or to dive underneath ice. In contrast, most of us probably like to dive in less than 25 meters of clear warm water, without pushing their limits. But how many people hear about this?

Because the ‘normal’ freediver is hardly ever in the news, people that do not freedive do not know that this part of freediving exist. They believe that we must all want to dive deep, risk blackouts, and live on the edge. How do we change that mindset?

Some freedivers have recently questioned the rules for AIDA competitions. They say there are too many blackouts and this damages the image of the sport. Perhaps that is true. If the general public would never see a blackout, the image of freediving would surely change. However, I believe the responsibility is also partly ours.

“The responsibility to change the image of freediving is ours”

When we talk about freediving, we should aim to let people know that blackouts are not the norm. We don’t go out and expect one too happen. Rather, we train for the worst and dive our best. We mitigate the risk by knowing safety protocols, and minimize the risk by diving within our limits. The approach is similar in ocean kayaking, sport climbing, mountain biking, or any other sport.

Just as a side note: Whistler Mountain Bike park followed 2000 mountain bikers over a 5 month period in 2009. Nearly 50% of them were injured in that time. Of those, 108 injuries threatened life and/or limb. If I google for ‘mountain biking risk’ I see studies, risk assesments, and articles on mitigating risk. No bold statements such as ‘Deadly risk lurks behind the thrill of mountain biking, or ‘The dreadful (and unnatural) toll of mountain biking’.

Yes, blackouts happen. Yes, we train to hold our breaths longer. But that does not mean we disregard personal safety or are all adrenaline junkies.

Preventing and dealing with ear infections after freediving

I have had recurring ear infections since I started freediving. At first I would only get them after pool training, but later I also started getting them after ocean dives. I am unfortunately very prone to ear infections because of a narrow ear canal that makes it hard to drain my ears. For me, the war on germs is a necessary post-dive ritual.

This article is based on my and other freedivers’ experiences, but remember that I am not a doctor – if you have health concerns, do not rely on me for advice.

Symptoms of an ear infection after freediving

An ear infection is caused by bacteria in the outer ear. If water remains in the outer ear after a dive these bacteria can multiply and cause an infection. Usually these infections become apparent the day after the dive, gradually increase in severity, and then decrease again. During an ear infection you may experience some difficulty hearing through the ear affected, swelling of the lymph nodes in the neck (more prominent on the side of the ear infection) and headaches.

If you experience sudden pain in your ear during a dive, it’s not an ear infection but barotrauma. If you do not have an ear infection but another ear problem you may injure yourself further by using the methods below, so make sure you know what is causing you grief!

Prevention of ear infections

  • Rinse your ear with a natural oil (olive oil, coconut oil) prior to diving

Ear wax is a substance composed of oils and dead skin and is called cerumen. It protects the skin of your ear canal. By rinsing the ear with a natural oil prior to the dive session you reinforce the cerumen and make it less likely that germs or harmful substances make contact with the ear canal. I myself have not used this method but after the initial publication of this article, other freedivers mentioned this as a good prevention technique.

  • Drain your ears after every freediving session

The first thing to do once you come out of the water is to make sure you have drained all the water out of your ear. The water that remains in your ear, together with some ear wax and things that float in the water such as algae, are the perfect substrate for bacteria to grow and multiply on. Drain your ears thoroughly and you stand a much better chance of avoiding an ear infection in the first place.

  • Use a a solution with vinegar and/or alcohol once after freediving

If you are prone to ear infections like me, just draining your ears won’t work. Time to take out the bigger guns so that you do not give bacteria a chance. I use a 50% vinegar, 50% alcohol solution in my ears after dives. If I do this right away after a dive, I know I won’t get an ear infection. You can get rubbing alcohol from the pharmacy, and buy simple white vinegar at the grocery store. I use a dropper that used to have different ear drops in it to administer it. I keep the solution in my ear for about 5 – 10 seconds and then let it drain.

Ear infection
Simple rubbing alcohol. Mix this 50/50 with white vinegar and put one or two drops in both ears after a freedive, and drain. Works like a charm
ear infection
In case you use a dropper that was originally intended for something else such as an eye dropper, make sure that you label it. Your family or roommates won’t appreciate putting peroxide in their eyes.

Note that alcohol dries the ears. For this reason, some freedivers mix the alchol with coconut oil, or d not use alcohol in the mix. Rather, they choose to use alcohol and water. I am sure there are more out there, but here are some possible concoctions:

  • 33% alcohol, 33% water, 33% vinegar
  • 50% alcohol, 50% vinegar
  • 50% water, 50% vinegar
  • 80% alcohol, 20% coconut oil

If you do get an ear infection

If I forget to use the vinegar-alcohol solution, I stand a fairly big chance of waking up the next day with an ear infection. Here’s what I do if I get an ear infection:

  • Use a vinegar and alcohol solution every 4 hours

If I have a starting ear infection, I use a 50%/50% alcohol-vinegar solution every four hours. I lie down on the couch with the affected ear up, administer some drops and leave them in the ear for about a minute, and then let it drain. I do this every four hours during the day until the infection recedes.

  • Blast the bacteria with hydrogen peroxide

A very effective way to remove ear wax and kill bacteria is hydrogen peroxide. A topical solution of 3% hydrogen peroxide does the trick. Use a dropper to get 3 drops in your ears and let it sit for 5 – 10 minutes until draining. The hydrogen peroxide will liquefy the ear wax and bacteria that cause the infection so that it can drain out of the ear. This method is very effective, but does remove the ear wax, a protective lining that coats the ear canal. I only use hydrogen peroxide if I have excessive ear wax or if the ear infection is severe (excessive ear wax and a severe infection commonly go hand in hand).

Always label your droppers aprropiately!

Ear infection
Hydrogen peroxide. The bugs don’t like it. You ears may not either, but it does get rid of the infection. Don’t make using hydrogen peroxide a habit.
  • Go see a doctor

I commonly notice a result within a day or at least two days using the alcohol-vinegar solution and/or hydrogen peroxide. I recommend you see a doctor if the above methods do not work or if you have a serious infection. Although you can get topical antibiotics over the counter in some countries, I don’t recommend using antibiotics without prescription.

I’d love to hear your method of battling ear infections, let me know what works for you in the comments!

Win a free copy of Success and Failure by Sara Campbell

Woops you’re a bit too late! This competition ended on July 3rd 2017.

Here is your chance to win one of 5 free copies of Success and Failure by Sara Campbell.

Winning could not be easier.

  1. Leave a comment on this post for one chance to win
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You don’t get an extra chance to win for multiple comments, but you can have two chances if you both comment and sign up for our newsletter!

The competition will close on Monday July 3rd, 11.59 pm (UTC+0800), and winners will be randomly selected on Tuesday July 4th.

Don’t forget to share this post with your freediving friends!

In case you need convincing, read our review of Success and Failure here.

Woops you’re a bit too late! This competition ended on July 3rd 2017.

Success and Failure by Sara Campbell review

This review was written by Luca Malaguti.

The latest course by Sara Campbell, Success and Failure, touches on several familiar (and personal) issues that are relevant in freediving today. The idea that we are always being watched generates a polarity in people’s minds, one in which there are only two options: to succeed and break a record or to fail and be disregarded entirely. This is the mindset of many freedivers today. If they don’t break that new record, then all those personal achievements along the way, are forgotten.

There’s a beautiful old photo of Jacques Mayol standing on the edge of a small, wooden raft holding a large stone with a rope attached to the end of it. Practicing the ancient freediving art of Skandalopetra, he has no watch, almost no viewers, no judges, and no timekeepers. When I’m stressed about my performances, how good my breath-hold is, or how deep I went last time, I think of this photo and of how Jacques Mayol became a freediving role model, by increasing depth and time slowly, simply because he loved it and dove often.

Success and Failure is about the illusion that we must succeed for others and not ourselves. The illusion that we must set standards so high that anything which falls short is automatically a failure. If this means taking more time to go at a certain depth, even during a competition, then so be it. Like Aharon Solomons says, if you black out you went too deep, something went wrong and you should take a step back in your training. This is an issue in today’s freediving competitions because a lot of competitive freedivers black out several times before “succeeding” to hold up that white little card for a few seconds. Is this really success? By enforcing this mentality of “push at all costs” are we not slowly edging the sport into a world of cheating and doping?

Success and Failure
How do you cultivate a mindset that allows you to improve without focusing on the numbers? How do you deal with the setbacks that inevitably come on your way to the deep? It is all in Sara’s new course, Success and Failure

Sara’s course couldn’t come out at a better time. She makes her viewers re-think what success means, on an individual level and not on an AIDA roster. When we follow the standards set by our ego (influenced by external factors), then we are most likely to fail (or what we perceive as failure) and so this can generate, as Sara mentions, self-animosity. Grounded in fear and disappointment towards ourselves, self-animosity can kill our confidence and even our passion for freediving. No one, that I know of, has said this better than Henry Miller, “The mind is its own place and in itself, can make a heaven of hell, a hell of heaven.” Sara’s courses help deal with this; they re-establish a notion that of what counts by focusing on the self. You sat down on that mat, you held that breath, you ended with a smile on your face and not a frown. That joy is addictive and will motivate you to continue this practice.

Sodarshan Chakra Kriya is a challenging exercise for people, such as myself, that need the depth of a cold and dark body of water to enter a state of focus. Poolside statics are not enough for me to relax at times, whereas a hang at depth can do so. However, it’s important that we address these problems and, like Sara mentions, “clean out the closet of our subconscious”. If we’re not able to sit down on a mat and focus, or our mind runs wild with other thoughts, then this exercise can help. It’s challenging at first, to focus on repeating the phrases “wah-hey guru” in your head and staring at the tip of your nose. But after a while, your rambling thoughts will funnel into clear focus.

Success and Failure

Success and Failure is the combination of ancient practices that have been refined to perfection over thousands of years with today’s modern problems. Everything we do is under scrutiny, recorded by a camera or mentioned in a forum. This polarizes sports: you’re good enough or not. Freediving transcends this however, and requires a great deal of patience, especially with ourselves. To set standards according to others and not ourselves is a recipe for failure. Listening to our inner voice and overcoming this idea that we must be perfect in everything we do is how we succeed, even if by minute increments.

As Herman Hesse’s Siddhartha beautifully explains this, “Wisdom is not communicable. The wisdom which a wise man tries to communicate always sounds foolish…Knowledge can be conveyed, but not wisdom. It can be found, it can be lived, it is possible to be carried by it, miracles can be performed with it, but it cannot be expressed in words and taught”.

Go to Yoga for Freediving (external link)

Other courses in the series:

A practical guide to apnea walking as training for freediving

You have probably heard about apnea walking as a form of training. But how does it really work? What are you actually training? There are a few specific ways to practice apnea walking. Here I will describe the method I use.

As you know from our previous posts on muscle fiber type, and muscle metabolism, different metabolic pathways and muscle fibers are active during different parts of the dive. With apnea walking, you train the ascent phase of your dives. During the ascent phase, your legs are gradually becoming more hypoxic as a result of vasoconstriction and overall oxygen depletion.

If you feel like your legs are always tired when you are coming up, apnea walking is worth a try.

Should I practice apnea walking with full or empty lungs?

Apnea walking is a good way to train the muscles under hypoxic conditions. If you do a static with full lungs, your oxygen saturation only starts to decline after several minutes. It starts to decline within a minute if you do a static with empty lungs. The same thing happens if you are walking. Empty lung apnea walks result in lower oxygen saturation, and will be shorter as a result.

Because I find the dive reflex is hard to initiate on land, I do most of my dry apnea with empty lungs. I always train with an oximeter. If the goal is 85% SaO2 it does not matter whether I get there with full or empty lungs.

For me, training with empty lungs is faster and more comfortable. If you have no problem doing long full lung breath holds on land you can fully inflate your lungs before apnea walks.

apnea walking
A simple oximeter that I use for apnea walking. It is far from perfect, but definitely allows me to track my performance better.

I use an initial static of around 30 seconds to become slightly hypoxic before I start the walk. The reason for this is that my body might maintain blood flow to the muscles if I start walking prior to the onset of the dive reflex (or HR drop). This is an obvious issue if the goal is to train the muscles under hypoxic conditions.

After my 30 seconds empty lung static I walk for approximately a minute while maintaining the breath hold. At the end of my static I try to be at SaO2 80 – 85%. I take about 10 recovery breaths, and note the final SaO2. My total recovery interval is 1:30 between walks. I get a maximum of 5 contractions per breath hold this way and I can easily keep it up for more than 10 repetitions.

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Empty lung apnea walking

Apnea walking in point form:

Get your oximeter and a timer ready. If you do not have an oximeter you can still do the exercise but it will be harder to tweak it to your needs.

  • Warm up with a couple breath holds or simply breathe slowly for a few minutes
  • Do an initial static
  • Walk
  • Take up to 10 recovery breaths (quick breaths) and relax. Your total recovery interval is 1:30
  • While in recovery the numbers on your oximeter may keep dropping. Note the lowest value. If this value is lower than your target, reduce your next static and/or walk
  • Repeat for 12 cycles

I use the ‘runtastic’ timer app for iOS in order to time my training (I am not affiliated with this app in any way).

I use the runtastic timer app for my apnea walks
I use the runtastic timer app for my apnea walks

Tweaking the exercise

Your initial static should be short enough to allow for a decent walk. If you have a strong dive reflex on land you may not even need the static. I suggest starting the static at 30 – 50 % of your onset of contraction time. For example a diver that gets contractions at 1 minute on an empty lung static should start with a static of 20 – 30 seconds. If you have an oximeter with heart rate monitor, stop the static and start the walk when you see your heart rate drop (if you see a heart rate drop at all – I often don’t).

Your oximeter will not show the current oxygen saturation. Rather, it records a moving average. Because of that you will have to keep checking your oximeter during your recovery. The lowest value should show up within 15 seconds after you start breathing. Compare this value to your target value.

Your apnea walks should be of a comfort level that you can keep up for more than 10 repetitions. The reason is that you are simply not going to induce adaptations by only one minute of hypoxic walking per training session.

Before you start training, know the risks. Any exercise involving apnea can lead to loss of consciousness, injury, or even death. Choose a safe site to train. Do not attempt this training with a heart condition. Always train with a buddy/spotter.

How do you train your apnea walks? Leave a comment!



Freediving buoyancy and its effect on energy expenditure

How much energy do we really expend during a dive? This was a question posed by Connor, after our last post on muscle metabolism (Part 1, Part 2). This article is the result of that question. Perfect freediving buoyancy is nearly a science on its own.

How much energy does a dive cost if you are wearing a wetsuit? How much less energy if you decide to dive on an exhale instead of an inhale? In this post, we will look at freediving buoyancy and how much energy you burn going up and down. The results may surprise you!

Try to imagine you are a perfectly average male (sorry ladies). You are the embodiment of averageness. You are 80 kg, (176 lbs), 1m 75 (5’10”) and have approximately 15% body fat and perfectly standard lungs with 1.2 liters functional capacity, 2.3 liters functional residual volume, 5.8 liters normal full lungs and 8.5 liters packed lung capacity. I realize that there is a small chance that you are not, for whatever unfortunate reason, completely average. That’s ok, even though body composition matters, lung inflation and the thickness of your wetsuit matters even more.

Let’s have a look at what affects freediving buoyancy.

Freediving buoyancy: body composition

Your body composition has a significant effect on your buoyancy. Fat is somewhat buoyant, muscle is somewhat negatively buoyant and bones are very negatively buoyant. Other soft tissues have a density close to that of water. The density of the body without any gas in the lungs (or intestines) is somewhere in between 1.01 – 1.08 g / cm3. This is always heavier than fresh water, and usually heavier than salt water. Our average diver has a density of 1.05 g / cm3.

Freediving buoyancy: the lungs

The lungs are compressible, and this causes their effect on buoyancy to change with depth. There will always be a net positive buoyance from the lungs. This positive buoyancy is great at the surface, but small at depth.

Freediving buoyancy
The body has a specific buoyancy (x-axis) which does not change with depth (y-axis). You can see that the net effect of the lungs is always a positive buoyancy force. However, the magnitude of this force declines drastically with increasing depth. The change in buoyancy is largest close to the surface.

Freediving buoyancy: neoprene

Your wetsuit is made of neoprene. Neoprene without any bubbles in it has a density of approximately 1.3 g/cm3. The wetsuit is made supple and insulating by injecting the neoprene with nitrogen. All these nitrogen bubbles add buoyancy. Neoprene can contain anywhere from 30% to 94% nitrogen. More nitrogen means a stretchier wetsuit that is more insulating at the surface, but less insulating at depth. Here I assume a neoprene nitrogen content of 84%, and a base density of 1.3 g/cm3, leading to a final density of 0.24 g/cm3. These numbers were obtained with some help from friends at Azure Passion. (I am trying to get more detailed specs on a variety of neoprenes, if I succeed, it will be added or linked to here).

Weight, or uncompressible buoyancy?

The last variable, which is the easiest for us to change, is how much weight we carry with us. Some divers also decide to take down uncompressible buoyancy. This basically counts as negative weight. I dive with 600 grams of positive buoyancy (incompressible plastic spheres) in my fin, in addition to 13 pounds of lead on my neck and waist, so that my legs float and I can stay vertical during my descent. But how much weight should we use in total?

freediving buoyancy
Neoprene has an effect on buoyancy that is similar to that of the lungs. Neoprene is always positively buoyant (in a freedivers depth range). Lead of course has a resulting negative buoyancy force, which is constant.

Energy cost of freedives

We should be weighing ourselves so that we can minimize the work we do during a dive. Work is defined in physics as ‘W = F x a, or work equals a force times a distance. If the buoyancy force of your body, Fb = 20 during your entire dive, and you dive to 20 m, you have to expend 20 x 20 = 400 joules (approximately 50 calories) to dive down to 20 meters.

On the graphs in this article, the distance (depth) is plotted on the y-axis, and the force resulting through buoyancy is plotted on the x-axis. The area underneath the curve is the amount of work that a diver has to do to get to a specific depth. This makes intuitive sense, because the higher or lower a buoyancy force is the more work has to be done in order to counter that force. If a diver is very negatively buoyant, it costs a lot of effort to come to the surface. If a diver is very positively buoyant, it will cost a lot of effort to dive down.

In the following graphs you can see a hypothetical 130 m dive, which is close to the current CWT record of 129 m. These curves are for divers with full lungs, and a variable suit. The divers have been perfectly weighted in order to minimize the area under the curve.

freediving buoyancy
Here are a set of hypothetical 130 m dives by our average diver. The suit is variable. If the line is close to x = 0 (indicated with the top arrow), the buoyancy is small and the total energy expenditure is small too. The simple conclusion is that a dive with no suit is much more energy efficient than a dive with an 8 mm suit. A more interesting conclusion is that in order to be weighted properly, divers need to bring positive buoyancy with them, rather than lead weight (which is negatively buoyant). The amount of weight required is indicated on the legend. The minus sign indicates that the weight is negative!

An interesting thing to note is that all divers are neutrally buoyant at half their target depth. This is a recurring finding, for any depth, and holds for any combination of suits, lung fill, body types, and weight.

Another interesting thing to note is that without using incompressible buoyancy,  all divers (except the diver with the 8 mm suit) are too negatively buoyant in order to be diving to 130 m. They will reach neutral buoyancy too early, and hence waste effort on the ascent. For example, our no suit diver requires 1.2 kg of positive buoyancy in order to be perfectly weighted.

A no suit diver expends approximately 822 J (200 cal) on the ascent and descent if perfectly weighted (1.2 kg positive buoyancy). If the diver decides to carry no weight, this increases to 1500 J.

Of  course no freediver in his/her right mind would attempt a 130 m dive in an 8 mm suit. The buoyancy force of a ‘perfectly weighted diver’ in an 8 mm suit at the surface is so high, that it would be close to impossible to dive down to any depth. The diver has to strap on half a ton of weight to make the descent possible. All this weight makes the ascent next to impossible.

Energy cost of 25 m freedives

I know, you don’t dive to 130 m, and I don’t dive to 130 m either. So what do people other than Alexey Molchanov and Guillaume Néry take away from this study? My last recreational dive session averaged 24.5 m, so I will focus on 25 m dives here.

Here is a plot for divers that dive on full lungs with a variety of suits:

freediving buoyancy
The buoyancy force plotted against depth for 25 m dives with full lungs and a variable suit. Note that diving without a suit is much more energy efficient than diving with an 8 mm wetsuit.

Keep in mind that the area in between the curve and the y-axis corresponds to the total energy expended. Because the curve is far away from the axis above neutral buoyancy (12.5 m), this is where we lose most of our energy.

And here is plot for divers with a 3 mm suit, that dive on 1) a forced exhale, 2) a passive exhale, 3) full lungs, and 4) packed lungs:

freediving buoyancy
The buoyancy force plotted against depth for 25m dives with variable lung inflation and a 3 mm wetsuit. Note that diving with packed lungs costs nearly as much energy as a dive with full lungs with an 8 mm wetsuit! FV  implies a forced exhale.

What do we learn from this? Well, the first lesson is one that you probably already know. Your suit should be as thin as possible, because it takes a lot of effort to dive with a thick suit. Second lesson, if you bring down less air your dive will be more energy efficient. Yes, you read that correctly. A forced exhale is much more energy efficient than packed lungs, and the difference is big. Our diver expends less than half of the energy diving after a forced exhale, as opposed to diving after packing. Apart from that, after an exhale, our diver only needs 0.3 Kg to be perfectly weighted, and after packing our diver needs  3.6 Kg!

If you do dive with a thick suit you can offset the extra buoyancy by diving FRC (functional residual capacity, this is diving after a passive exhale). Note that a diver with packed lungs and a 3 mm suit nearly expends as much energy as a diver with an 8 mm suit with full lungs! A diver with an 8 mm suit on FRC expends approximately 476 J on overcoming buoyancy, and a diver with a 3 mm suit and packed lungs expends 465 J on a 25 m dive.

Of course, the significant downside to diving FRC or even RV (residual volume, or diving after a forced exhale) is that you will not carry as much oxygen with you. Some divers feel that the sacrifice is worth it. However, I do not know of any recent records that have been set with an FRC dive, so it appears that oxygen (or perhaps equalization) is a limiting factor for dives to great depth.

Practical tips

  • Aim for neutral buoyancy at half of your target depth. During a dive session in which you dive 20 – 30 m, with 25 m dives on average, aim to be neutral at 12.5 m. A more conservative approach is to be neutral at half of your maximum expected depth (15 m). If you pack, and/or use a thick suit, this is especially important.
  • If you have no problems with lung or trachea squeezes, explore FRC or even RV diving. It may be more comfortable for you. Several threads on the Deeper Blue forums are devoted to FRC diving. RV diving has recently been suggested by Aharon Solomons as a method to acclimatize to depth. Always dive with a buddy and be very careful, because you are missing out on a large oxygen reservoir and are more prone to squeezes.

In a future post I will show you how much energy I burn in an average dive session.


















Training and Performance by Sara Campbell review

This post was submitted by Luca Malaguti.

In Training and Performance Sara guides you through a series of hands-on and practical exercises that apply to all facets of freedive training. I really like that Sara starts off the program by explaining a few things we tend to forget in athletic training, and especially in freediving.

Cultivating continuous improvement

Sara teaches us about the balance between sustainability and challenge. We should strive for continuous gradual improvement. In order to achieve that we need to set attainable goals that gradually lead to improvement. Setting the bar too high may lead be demoralizing, undermine our confidence, and take the enjoyment out of the dives.  Sara emphasizes that it is important to advance patiently and step outside of our comfort zone during training, but not venture too far beyond it, in order to allow for continuous progress.

'Yoga For Freediving' is a series of online yoga courses by Sara Campbell
‘Yoga For Freediving’ is a series of online yoga courses by Sara Campbell

Just as many positions (asana) in hatha yoga seem intimidating at first, breathing exercises (pranayama) can be equally daunting. Recall your first wobbly downward dog? However, Sara presents the exercises in a way that they gradually become more complicated and demanding. This I particularly appreciate. For this reason her video lessons are very effective. You have a mentor in front of you guiding your practice step by step. A lot of the exercises Sara goes over I have read them in books many times over, but having Sara in front of me belly pumping for 3 minutes pushes me to keep up with her and advance my practice so that I feel those new sensations. On my own I would probably stop after 60 seconds.

Training and Performance videos

Sara’s course contains 6 specific videos:

  • Training zone (~10 min lecture)
  • Comfort zone (~10 min lecture)
  • Pranayama – basic breath series (~45 min breathing exercise)

I found it effective to start with a few breath cycles before starting alternate nostril breathing. This way the nasal cavities are somewhat clear before the alternate nostril breathing exercise. Alternate nostril breathing is an important exercise to begin your practice with because it gets you “in the mood” to continue. Whether it is the effect of nitric oxides or just an overall cleansing sensation, this exercise first thing in the morning can really put a smile on your face.

  • Kriya – basic spinal energizer (~50 min exercise)

The spinal energizer is a truly fantastic exercise. However, if you find it painful to sit in the lotus or the partial lotus position (for example because of a knee injury, my problem), you can try sitting down with your bum touching your heels. This is known as vajra-asana or position of the diamond. This position may help to relieve some of the tension on the knees generated by the twisting.

  • Respecting your body (~10 min lecture)
  • Visualization – perfect dive (20 min exercise)

Training and Performance also comes with more than 20 extra videos and other materials to help you with your practice. The lectures and visualisation are available in MP3 format so you can bring them with you and listen to them before you dive, or on the road.

Training and performance
Training and Performance is the 4th part of Sara Campbell’s ‘Yoga For Freediving’ series.

In Training and Performance Sara goes over excellent exercises that connect movements with breath. I look forward to using them to advance my practice in freediving, while enjoying having my teacher in front of me guiding and motivating me through my practice. The way that Sara interacts with her viewers brings them by her side, and allows them to imagine a morning of diaphragm exercises on the beaches in Dahab.

Go to Yoga For Freediving by Sara Campbell (external link)

Other reviews of Yoga for Freediving by Sara Campbell





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