What cardio can do for freedivers and spearfishers
Jimmy J. taking a final breath before his 40 second hang at 75 meters in Soufriere Bay, Dominica.

What cardio can do for freedivers and spearfishers

This article will take approximately 7 minutes to read.

Highlights

  • Understanding benefits of increased VO2 max and lactate threshold
  • Cardio’s effect on O2 storage and CO2 tolerance
  • Cardio is effective for depth training, maybe less for pool training

Humans are masters of endurance exercise. Research suggests we very likely evolved to run long distances. But what can running and other cardio exercise do for us? Let’s understand the metabolic requirements involved for recreational and competitive diving first.

Here’s a fantastic short film about a tribe that still runs animals to death.

Competition or repetition

Recreational divers and spearfishers commonly do not go ‘all out’ on any of their dives. Rather, they dive for hours on end within comfortable limits. Aerobic metabolism is largely what allows them to do so. Lactic anaerobic metabolism occurs too, but to a lesser extent.

Competitive freedivers train for single maximum performances. These performances leave them hypoxic and lactic. The metabolism in their muscles is anaerobic during a very large part of their target dive.

Note: I’m not going into the ATP-CP system here, because it is used in both types of diving. If interested you can find more about it here.

How to gauge cardio performance

There are two performance markers that you’ll hear over and over when you start to look into cardio training. VO2 max and lactate threshold. Let’s try to understand both and how they relate to cardio as well as freediving.

VO2 max

VO2 max is the maximum amount of oxygen your body can use during exercise in a given time. It is a measure of how efficiently oxygen can be delivered to working muscles. Things that affect VO2 max (amongst others) are: 

  • Breathing

Breathing muscles allow for oxygen to get into our bodies in the first place, and control the volume of air that is replaced with every breath.

  • Quantity of red blood cells

Red blood cells transport oxygen. If you have more, you will be able to transport oxygen more efficiently. 

  • Myoglobin abundance

Myoglobin transports oxygen from the red blood cells to the mitochondria.

  • Mitochondria  

Mitochondria are the energy factories within cells. Oxygen is used here to produce energy.

Any of the above four can be a limiting factor on performance. For example, you can have a lot of red blood cells, but if you do not breathe efficiently your VO2 max will still be low.

Lactate threshold

The muscles always produce a little bit of lactate. However, lactic metabolism only becomes the dominant metabolism during exercise of high intensity (read more about lactate here and here). The lactate threshold is defined as the intensity of exercise at which lactate starts accumulating in the bloodstream.

To put this differently, if you have a high lactate threshold your muscles are able to process more lactate at any given time.

Effects of cardio for freedivers

Cardio has all sorts of benefits. It increases blood volume, causes neurogenesis, increases the elasticity of blood vessels, and lowers cortisol (a stress hormone), to name but a few. But what does it do for freedivers?

O2 storage

By increasing blood volume, red blood cell count and myoglobin, you increase the total storage volume of O2. The effects of increased O2 storage on freediving are simple: longer dive times. More effective transport of O2 in cardio training translates to more storage of O2 for freedivers.

An interesting fact to ponder: cetaceans, who dive all day within comfortable limits, grow more slow twitch muscle fiber as they age. This helps them dive for longer (full study).

CO2 tolerance

Red blood cells are important for CO2 tolerance. CO2 produced in muscle cells can either be bound to hemoglobin, or converted there to bicarbonate ion. In these two ways red blood cells facilitate the transport of CO2 to the lungs.

The CO2 that is not bound to hemoglobin or converted to bicarbonate remains dissolved in blood plasma. From there it can diffuse to the central chemoreceptors. In our previous article, we speculated that central chemoreceptors play a vital role in triggering contractions. Therefore, if we can facilitate more CO2 to be transported as CO2 bound to hemoglobin, or bicarbonate, we may be able to dive without contractions for longer.

Decreased recovery time & muscle fatigue

By increasing the lactate threshold, we are able to accumulate less lactate during dives. Our muscles will process more lactate while we are diving. This leads to a decrease in recovery time both in between dives, as well as between diving sessions.

Muscle fatigue during a dive (most commonly leg burn) also reduces as a result of a higher lactate threshold.

VO2 max training effects in the pool and at depth

A common question we hear from freedivers about VO2 max is: “Wouldn’t an increase in VO2 max cause me to go through O2 faster during a dive?”. This is a good question with two answers. No, for depth dives, and maybe for pool dives.

Let’s say a long distance runner, adapted for runs longer than 10km decides to go freediving. The runner’s muscles are composed mostly of short twitch muscle. This means that they are well vascularized, and oxygen is transported to them swiftly and efficiently.

During a pool dive or static, blood shift and peripheral vasoconstriction will not counteract the increased vascularization of the muscles as well as during a depth dive. It is certainly possible that cardio is not the training of choice for pool divers.

During a depth dive, blood flows from the peripheries to the capillaries in the lungs. This counteracts the decreasing lung volume and protects against squeezes. And hence, with a bit of help from blood shift and vasoconstriction at depth, you don’t have to worry about a high VO2 max. In fact, it may very well help you.

 

freediving, apnea, training, cardio, alberta, canada, dominica, soufriere, freedive, trail run, alpine
Above: Alpine trail running in Kananaskis Valley, Alberta. Below: Deep freedive training in Soufriere Bay, Dominica. || Photos by: Luca Malaguti (Sea to Sky Freediving). ||

Jaap

Jaap is a geologist by trade and a freediver by passion. Jaap wrote the book Longer and Deeper in 2018. His book teaches how to train for freediving and spearfishing on land.

This Post Has 4 Comments

  1. Connor Davis

    Thought provoking article.

    I had not thought of the mechanism binding c02 to hemoglobin as improving with cardio and how that reduces c02 in the bloodstream.

    That leads to a question. Once the c02 is offloaded to the lungs, the cnc of c02 in the lungs must rise and increase the gradient across the alveoli. Eventually does that slow down c02 transfer and increase dissolved co2? Since there are no chemoreceptors in the lungs, there should be no limit to how high the co2 concentration can go relative to diver discomfort. Has anybody studied this?

    I gotta do more cardio.

    1. Jaap

      Hey Connor, excuse the late reply. CO2 and hemoglobin are definitely very much related and more hemoglobin is good for CO2 tolerance.

      You’ve got some really good questions there. I think that the chemical offloading of CO2 proceeds continuously as O2 has a higher affinity for hemoglobin the two are constantly exchanged. However, because the CO2 concentration in the lungs increases, diffusion of CO2 from the lungs into the bloodstream must also increase (dissolving of CO2 into blood plasma is about 20x faster than dissolving of O2). The two effects may simply cancel out each other.

      I don’t think there are any studies that have tried to quantify this. However, the constants are known so the calculations should be possible (I haven’t taken the time… yet).

      Go for a run! It’s the most natural cardio you can do, you need minimal gear, and if you’re over it you can just start walking :).

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