Tag Archives: apnea walks

Training for freediving with the Moxy muscle oxygen monitor

This post goes with a webinar that I gave on data collected with the Moxy Muscle oxygen monitor. In the webinar I test some specific exercises and try to speculate on myoglobin desaturation and training to increase myoglobin stores.

I want to use this post to give some extra thought to some keypoints, and to make the webinar a bit more understandable. But first, keep these things in mind:

  • The Moxy measures oxygen in the muscles. I put it on my left Vastus Lateralis (quadriceps).
  • The Moxy gives you one number for total SmO2 (muscle oxygen). This number is a weighted average of myoglobin and hemoglobin.
  • Everything I tested only relates to me and my (left) quad. The numbers will be different for you. The squats that work for me may not work for you. The apnea walks that don’t work for me may work for you.
  • On all the graphs in the presentation, the x axis = time in seconds. The left y axis is for heart rate, muscle oxygen and SaO2. The right y axis pertains to Thb and is a measure of blood flow to the muscles.

Ok now you can watch:

I used the Moxy to test a series of exercises. What do these exercises actually do?

Apnea walks

For example, the apnea walks that I described here actually did not train my muscles to perform under hypoxia at all. The body has a fantastic set of feedback mechanisms in place to make sure that oxygen is delivered where it is needed, and without the vasoconstriction and blood shift during a dive that oxygen will go right into your muscles. Apnea walks debunked. Sorry everyone.

It didn’t matter whether I did them on an exhale or inhale.  I think that apnea walks on an inhale probably don’t work for anyone. On an exhale, they may work for some people, but I doubt it.

What about holding your breath until contractions and then starting exercise? Same thing. The muscles actually never get hypoxic. In fact, even doing this with a more strenuous exercise like a wall sit the muscles never dipped below ~35 %.

Doing a wall sit or even one-leg stand with breath did not help either. You can do a wall sit until failure, but there will be plenty of oxygen in your quads. It’s not a lack of oxygen that causes your muscles to fail, it’s the accumulation of waste.

RV squats

The only exercise that I found effective was a set of isometric squats with short recovery intervals, done after a forceful exhale. Using these squats and tinkering with the variables (length of recovery, initial static, and squat) I was able to consistently let SmO2 dip below 10%.

Now before you all start doing a 150 kg squat on breath hold, remember that if you do this with too much resistance you might simply be training for fast twitch muscle. If I focus on slow twitch muscle I try to stick to no higher than 30% of my personal max resistance.

How do you know this works? Are you increasing myoglobin in the muscles?

I don’t know if this works. But here is my rationale. In order to get the body to generate hemoglobin (red blood cells) you need to desaturate the blood of oxygen. This is why being at altitude increases your red blood cell count. The body will automatically create more red blood cells once it realizes it does not have enough of them to efficiently bring oxygen to where it is needed.

Along the same lines of logic, we need to desaturate myoglobin of oxygen in order to tell the body to create more of it. This happens naturally on some deeper or longer dives thanks to vasoconstriction and blood shift, but is hard to achieve when cross training.

I can’t promise you that by lowering SmO2 you will cause more myoglobin to be generated. I do think it is a sound hypothesis. Keep SaO2 high, and decrease SmO2. This is what naturally happens in our bodies during a dive, and one of the things to aim for during cross training.

The in-water method of training for myoglobin is called the Foundational Training and described in Eric Fattah’s book Holistic Freediving.

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!

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