Do Warm-Up Dives Actually Improve Freediving Performance?
What If Your Warm-Up Is Making Your Big Dive Worse?
AIDA & Molchanovs Instructor Trainer
He is the founder of The Depth Collector and VD Freediving Taiwan. With over a decade of experience, he focuses on solving real-world freediving problems, from equalization to depth adaptation, using practical, field-tested methods.
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If you’ve ever spent time on a freediving buoy, you’ve seen the ritual. A shallow dive, a little floating, perhaps something slightly deeper, a relaxed hang, another descent “just to feel things out,” and then, finally, the real dive.
We call them warm-up dives.
Most freedivers don’t question them very much. They tend to do what they have seen other divers do, as if the whole routine had been quietly passed down from one buoy to the next.
I am not particularly good at leaving things unquestioned.
My approach to training keeps evolving as I do, depending on whether I’m getting fitter while preparing for a triathlon or becoming slightly lazy and allowing life’s many delicacies to distract me from my athletic ambitions. And then, of course, there is the small matter of being 47 and discovering that age has begun, rather impolitely, to remind me that it exists.
For quite a while, my approach before a big dive was very simple:
I didn’t warm up.
I liked arriving at the dive fresh-ish, calm-ish, and not already slightly tired from preparing myself not to be tired.
It often worked for me.
At least, I thought it did.
But let’s be clear: that wasn’t science. It was me experimenting on myself and building an approach around what seemed to work.
No warm-up. Save the legs. Save the lungs. Go down.
Slightly heroic. Beautifully simple.
The problem is that physiology rarely has the courtesy to remain beautifully simple.
Warm-ups can produce effects that are genuinely interesting for a freediver. They can stimulate splenic contraction, influence heart rate, help us settle mentally, test equalization, rehearse technique, and alter the physiological state in which we begin the next apnea.
But they are not free.
They can also mean muscular work, oxygen consumption, glycogen use, heat loss, additional compression, time, and physiological load before the dive we actually care about has even begun.
I no longer think it is simply a matter of deciding whether warm-ups are good or bad. That is far too crude.
The question I care about is this:
What does this warm-up actually give me that will still be useful when I begin the dive that matters?
Because if the answer is nothing...
Why are we actually doing it?
Before Reading
How do you warm up before a deep dive?
Slow FIM dives
FRC dives
Hangs
A mix of everything (chaos, basically)
Why Are We Even Warming Up?
For some divers, warming up is about the mammalian diving response. For others, it is equalization, anxiety control, technique rehearsal, or simply convincing the brain that “yes, we are voluntarily going deep today, don’t panic.”
And that distinction matters, because we call all of these things warming up even though we may be trying to achieve completely different things.
A warm-up for mouthfill practice is not the same as preparation for a maximal depth attempt. A technical session is not a PB attempt. RV training is another thing entirely.
So before deciding how to warm up, there is probably one annoyingly important question to answer:
What are you actually training today?
Because if the goal changes, the warm-up probably should too.
For me, a warm-up only makes sense if something useful carries over into what comes next.
Keep that thought.
We are going to need it.
Do We Need to “Activate” the Diving Response?
You’ve probably heard this one:
“I need a few dives to activate my mammalian diving response.”
First dive: wake-up. Second: better. Third: now we’re in the zone.
I used to think about it that way too, like there was some internal switch that needed a couple of rehearsals before the body finally “took things seriously.”
Except physiology doesn’t really support that simple narrative.
The diving response isn’t one single response anyway. It is a collection of different physiological reactions.
So when somebody tells me they want to “activate the diving response,” I discreetly roll my eyes and think:
Which one?
Research by Erika Schagatay and colleagues gives us something particularly interesting here. Forty-one subjects performed five maximal apneas with facial immersion, separated by two-minute intervals. Across the series, apnea duration increased by 55%, yep, that is a lot , while the onset of involuntary breathing movements was delayed by 27% in the subjects in whom it could be identified.
(Schagatay et al. (1999). Effects of repeated apneas on apneic time and diving response in non-divers)
But here is the really interesting part: the cardiovascular diving response did not simply become stronger and stronger with every apnea.
Heart-rate reduction was actually most pronounced during the first apnea, while the reduction in skin capillary blood flow was strongest during the second.
The researchers concluded that the improvement in breath-hold duration was associated with physiological factors related to CO₂ accumulation and psychological factors related to tolerating the respiratory drive, not with an increasingly strong diving response.
Now, these were maximal apneas at rest with facial immersion in 10°C water, not depth dives, so we should be careful about translating the result directly to a 70 m constant-weight attempt.
But it does undermine the simplistic idea that every additional warm-up just keeps “switching on” more and more of the mammalian diving response.
Repeated apnea may leave us with something useful. Fine. But what?
That is the part I care about.
So let’s break the diving response apart.
Bradycardia 💙💙💙
Bradycardia is the reduction in heart rate during apnea.
Sounds pretty useful.
A lower heart rate can reduce oxygen consumption, and the response can begin rapidly during apnea and facial immersion.
For me, experiencing that slowing of the heart during a preparatory apnea also helps me enter that very particular freediving state. The heart slows down, the body settles, and the noise disappears a little.
You start getting in the zone.
Psychologically, that matters. Calm body, calm mind, less unnecessary tension.
What interests me is the state it helps me enter.
So yes, this is one response I am perfectly happy to experience before going deep.
I’ll take that one.
Peripheral Vasoconstriction 💔💔💔
Peripheral vasoconstriction can develop early in the dive and become stronger as oxygen levels fall, progressively reducing blood flow to the working muscles so that precious oxygen is preserved for vital organs such as the brain and heart.
Hypoxia appears to play an important role in strengthening this response. In a study comparing apnea under normal, hypoxic, and hyperoxic conditions, peripheral vasoconstriction was greatest during hypoxia and considerably weaker when oxygen availability was high.
The researchers concluded that falling oxygen contributes to the response, at least partly through stimulation of the arterial chemoreceptors.
CO₂ appears to matter too.
A particularly relevant 2026 study looked at blood flow in working leg muscles during apnea. When researchers lowered CO₂ before the breath-hold, the reduction in leg blood flow was significantly smaller. The authors concluded that arterial CO₂ is an important modulator of apnea-induced vasoconstriction in exercising muscle.
So as the dive progresses, falling O₂ and rising CO₂ can both contribute to stronger restriction of blood flow to the working muscles.
And those muscles still have a job to do.
As oxygen delivery becomes increasingly limited, the contribution from glycolytic metabolism can increase. Muscle glycogen is consumed, lactate and other metabolites accumulate, and the muscles begin to move away from their completely fresh state.
Your glycogen stores are obviously not going to disappear because of a few warm-up dives.
That is not my argument.
My argument is much simpler:
Why spend it if you don’t need to?
Think about a deep constant-weight dive.
You kick through the first part of the descent and eventually enter freefall.
Beautiful. Cheap. Almost free energy.
Then you turn.
And suddenly gravity is no longer your friend.
Those same legs now have to bring you all the way back to the surface while oxygen availability becomes progressively more limited.
That is exactly when I want them fresh.
If I perform several demanding warm-up dives beforehand, some muscular work has already been done, and recovery has already entered the equation.
Do I really want to repeatedly make my legs work under increasingly restricted blood flow before my biggest effort?
Weeeell...
Not if I can avoid it.
Maybe the cost is small.
Probably very small.
But maximal freediving is a sport where we happily obsess over tiny percentages, so I’m not going to suddenly pretend that small physiological costs don’t matter.
They do.
Blood Shift 💔💔💔
Then we have blood shift.
The almighty king of the mammalian diving response.
The legendary one.
As pressure increases and the lungs compress, blood is redistributed toward the thorax and pulmonary circulation, helping compensate for the decreasing gas volume inside the chest.
And the amount involved is not insignificant.
In classic experiments by Schaefer and colleagues in 1968, researchers measured increases in thoracic blood volume during simulated hyperbaric dives. In the single diver they studied, the increase was about 1,047 mL at 27 m and approximately 850 mL at 40 m under different experimental conditions.
These are not cumulative values, and they certainly do not mean every freediver shifts exactly one litre of blood.
But they give us a sense of scale.
Close to a litre of blood redistributed centrally. Pretty spectacular when you consider that an average adult male carries only around five litres of blood in total.
And when you are deep, that redistribution is essential.
No argument there.
But the warm-up question is different.
When freedivers perform a deep warm-up, an FRC dive, or an RV dive, the idea is often that they want to prepare the system for the greater compression coming later.
You trigger blood shift once, compress the lungs, expose the pulmonary circulation to pressure, recover, and then go deeper.
Okay.
So what carried over?
Does an FRC dive to 20 or 30 metres make the blood shift during my subsequent 70-metre dive develop faster?
Does it become larger?
More efficient?
More protective?
Does the first compression somehow make the pulmonary circulation better able to tolerate the second?
Those are not rhetorical questions.
I genuinely want to know.
Because blood shift itself is not the question. We know it happens. We know it matters.
The question is whether triggering substantial blood shift before my maximal dive improves what happens during the maximal dive.
And right now, I have not found convincing evidence showing me that it does.
That matters because very-low-lung-volume dives are not physiologically neutral.
In one study, 11 experienced breath-hold divers performed repeated empty-lung dives to only 6 metres over 20 minutes. Fresh blood originating below the vocal cords was found in two divers, while measurable reductions in lung function were detected immediately afterwards.
(Lindholm et al. (2008). Pulmonary edema and hemoptysis after breath-hold diving at residual volume)
Only six metres. On empty lungs.
Under those repeated low-lung-volume conditions, that was already enough to produce clear signs of pulmonary stress, including bleeding in two divers and measurable changes in lung function.
That does not mean an FRC or RV warm-up is automatically damaging.
Far from it.
I am a big RV lover.
(Wait... that came out weird.)
I mean, I love training this way myself.
But that is training.
Before a maximal depth attempt, I look at it differently. The pulmonary circulation is placed under substantial load, and the lungs are exposed to significant mechanical compression. If I then perform my maximal dive shortly afterwards, I am asking that same system to tolerate even greater compression.
Maybe that first exposure helps. (I have my doubts.)
Maybe there is some acute adaptation we simply haven’t measured properly yet. (Naaaan... not convinced.)
But if that is the argument, I want to know exactly what we gain from it.
Not tradition.
Not “everyone does an FRC warm-up.”
Not simply “I need to activate my blood shift.”
Show me what we are priming. Then show me the carry-over.
There is another potential cost to deep warm-ups that is easy to forget: nitrogen exposure.
Breath-hold diving is not immune to decompression stress. Decompression illness has been documented in freedivers, particularly with repetitive dives, short surface intervals, and deeper profiles. That certainly does not mean one deep warm-up is automatically going to cause decompression illness. But a deep preparatory dive still adds nitrogen exposure.
If I cannot identify a meaningful benefit from that warm-up, it is another cost I see very little reason to pay.
(Blogg, Tillmans & Lindholm (2023). The risk of decompression illness in breath-hold divers: a systematic review)
So a deep FRC, RV, or otherwise substantial warm-up before my maximal attempt?
Euhhh...
Nope. For me, that still looks like a pretty dumb trade.
I’ll skip over immersion diuresis, the magnificent freediving superpower of needing to pee approximately seven seconds after putting on your wetsuit, and move on to:
The spleen 💙💙💙.
The Spleen: The Best Physiological Argument for Warming Up?
The human spleen acts as a reservoir of red-cell-rich blood.
During apnea, it contracts.
In a study by Schagatay and colleagues, three maximal breath-holds reduced spleen volume by an average of 49 mL, or 18%. At the same time, haemoglobin concentration increased by 2.4% and haematocrit by 2.2%.
Forty-nine millilitres doesn’t sound like much.
But this is red-cell-rich blood, so even a relatively small release can measurably change circulating haemoglobin and haematocrit.
For us freediver, that is interesting.
More haemoglobin means the blood can potentially carry slightly more oxygen.
Not dramatically more.
You haven’t suddenly installed a second pair of lungs.
But during a maximal breath-hold, even a small difference becomes interesting very quickly.
So what actually makes the spleen contract?
It isn’t simply CO₂, and it isn’t simply low oxygen either.
Apnea itself appears to be an important part of the trigger.
Research comparing breath-holding and continued breathing under altered O₂ and CO₂ conditions suggests that stopping breathing contributes to splenic contraction beyond the effects of changing blood gases alone.
As the apnea continues, falling O₂, rising CO₂, and increasing sympathetic activation may strengthen the response further.
So instead of:
CO₂ rises → spleen contracts
the picture is probably closer to:
Apnea begins → splenic contraction develops → falling O₂ and rising CO₂ may strengthen it → red-cell-rich blood enters circulation → circulating haemoglobin temporarily increases.
And now we come back to our earlier question.
What carries over?
Well...
Here we finally have something.
The haematological effect of splenic contraction can persist after the apnea and change your physiological starting point for the next dive.
That is something I might actually want before my big dive.
Stimulating Splenic Contraction: Is It Worth It?
There is a common argument I keep hearing from defenders of the no-warm-up approach:
“Don’t waste your spleen on the warm-up. It will contract during the dive.”
I’m half convinced by that argument.
Yep.
Half!
The spleen is not a bottle that you empty once and then throw away. After it contracts, the red blood cells it releases remain in circulation for a period while the spleen gradually returns toward its resting volume.
And the timing is interesting.
In a 2023 study using repeated submaximal apneas, spleen volume and haemoglobin had returned to baseline within about five minutes.
After three maximal apneas, Schagatay and colleagues found that full spleen-volume recovery took approximately eight to nine minutes.
That does not mean five minutes, eight minutes, or ten minutes is some magical freediving surface interval.
What it does suggest is that there can be a useful period after preparatory apnea during which the haematological effect has not yet completely disappeared.
If I can begin my main dive with a slightly different haematological starting point...
I am interested.
Very interested.
But then comes the obvious question:
What did I have to spend to get it?
If I obtain that effect through depth warm-ups, my muscles work. I use glycogen. I produce metabolites. I lose heat. You know the list by now.
The splenic effect may be real.
But the method I use to obtain it is not free.
Well... maybe there is a way.
And now things get fun.
Wet vs Dry Warm-Ups: Now This Gets Interesting
A 2022 study by Vitali, Raffi, and Piras compared wet and dry warm-ups before a 75-metre dynamic apnea.
The wet warm-up involved considerable muscular work: 100 metres of kicking, eight 25-metre dynamic apneas, and two 50-metre dynamic apneas.
The dry warm-up included five minutes of controlled breathing, five minutes of thoracic and abdominal mobility, and four empty-lung static apneas.
Five minutes later, the nine participants completed the same fixed 75-metre dynamic apnea with fins.
The wet warm-up produced higher pre-performance lactate (2.60 mmol/L), while the dry warm-up resulted in lower lactate (1.93 mmol/L) and a slightly faster subsequent swim (70 versus 72 seconds).
Now, dynamic apnea is not depth diving.
That distinction matters.
And this study certainly does not prove that a dry warm-up is better before a deep dive.
But it does show us something important:
Your warm-up is not neutral.
Different protocols leave different physiological traces.
And suddenly another possibility appears.
If what I actually want before a deep attempt is splenic contraction and that slower, calmer state I associate with bradycardia, do I really need to dive to obtain them?
No, I don’t.
I can stay at the buoy, perform a few static apneas, stimulate splenic contraction, let the body settle, get into the zone, and potentially obtain much of what I want without kicking down to whatever depth, compressing my lungs, or getting colder.
And, conveniently, I love static apnea.
If two different methods can potentially give me the effect I want, I am increasingly attracted to the cheaper one.
I want to obtain the physiological benefit I need at the lowest possible cost.
That principle changed how I think about warm-ups.
And eventually, it changed what I actually do.
Depth Diving Isn’t Static Apnea
Before I turn all of this into an actual training decision, there is one rather large limitation.
Most of the research we have just discussed is not deep freediving research.
It involves static apnea, dry breath-holds, dynamic apnea, exercising apnea, or controlled laboratory conditions.
Useful?
Absolutely.
But a deep constant-weight dive adds pressure, lung compression, blood shift, equalization, changing buoyancy, freefall, the turn, muscular ascent, cold, current, and the psychological stress of depth.
During a static apnea in the pool, when you decide you want to breathe, you simply lift your head out of the water.
At 50 metres, wanting to breathe changes absolutely nothing.
You still have 50 metres to come back up.
That alone makes depth a very different physiological and psychological problem.
Many warm-up studies also compare one warm-up protocol with another rather than comparing warm-up with no warm-up during repeated actual depth dives.
So I am not going to pretend the literature has given us the perfect warm-up for a 70-, 80-, or 100-metre dive.
It hasn’t.
Nor am I going to claim that because preparatory apnea alters spleen volume or haemoglobin concentration, it has therefore been proven to improve maximal depth performance.
It hasn’t.
But the research has given us enough useful physiological clues to make better choices.
And after spending far too many hours reading about spleens, blood flow, haemoglobin, pulmonary compression, nitrogen, and people holding their breath in unpleasantly cold water...
I made mine.
So What Do I Actually Do Now?
I started writing this article as someone who generally preferred no warm-up before a big dive.
I still like the simplicity of that approach.
But the research on splenic contraction gave me something I had not really accounted for before: a potentially useful physiological effect that can still be present when the next apnea begins.
That was enough to change the way I prepare.
My logic is pretty clear: my warm-up has to match the job.
So rather than looking for one universal routine, here are a few examples of how I apply that idea in my own training.
Deep Dive
Before a deep performance dive, freshness is my priority. I want fresh legs. I want fresh lungs. I don’t want to create unnecessary hypoxic stress, and I certainly don’t want to add avoidable pulmonary stress with an FRC or empty-lung warm-up before the dive that actually matters.
But I am interested in the potential splenic benefit, and I like that slower, quieter state that apnea and facial immersion help me slip into.
So these days, I stay at the buoy and do three comfortable static apneas.
I don’t time them.
That is important to me.
The moment I start looking at a stopwatch, I know what will happen. I’ll begin comparing one static with the next, then one day with another, and before long I will have turned a warm-up into another performance test.
And that completely defeats the purpose.
Every day is different. Fatigue changes. Mental stillness changes. Sometimes the body settles quickly, sometimes it doesn’t.
So I go by feel.
I hold until I feel I’ve reached what I came for: calm, relaxation, that slower internal state I want before going deep. And somewhere in the background, the spleen is hopefully doing its little magic, contracting and releasing some of that delicious red-cell-rich blood into circulation.
I also use that time to practise some of the mental techniques I use during depth: body scanning, visualisation, and simply letting everything become quiet.
Three works well for me right now. Maybe you prefer two. Maybe four. Maybe one.
That is something you can explore for yourself.
Technical Training
Change the purpose of the session and my preparation changes with it.
If I am working on a technical dive to, let’s say, around 35 metres for example rehearsing my dive plan, or simply working on technique, I like doing a short FIM dive first.
Usually nothing more than an easy descent and a relaxed hang around 12 metres (My neutral buoyancy depth).
I really like those little hangs.
While I’m down there, I often visualise the dive in detail: the descent, the freefall, the turn, the ascent, the whole sequence.
And if you want to know a secret...
I usually pee in my wetsuit while I’m down there.
There. Now you know.
That little hang gives me a moment to settle into the water, check how my equalization feels, relax, and get a sense of what kind of day it is.
And because I am using FIM, I am barely asking anything from my legs.
RV Training
RV training is different again.
The goal here is not maximal performance. I am trying to improve diaphragm and respiratory-muscle flexibility, become more comfortable at very low lung volumes, and progressively expose my body to the kind of compression it has to manage deeper down.
That includes the mechanical side of things, but also the physiological responses that accompany compression, including the redistribution of blood toward the thorax and pulmonary circulation.
So I don’t add a separate warm-up.
I could do a relaxed hang or a slow FIM dive first.
But what would be the point?
I simply begin with shallow RV dives and progressively increase the depth as the session continues.
And really, those first shallow dives are already the warm-up.
Final Thought
So, do warm-up dives improve freediving performance?
Some of their effects clearly make physiological sense. Splenic contraction can increase circulating haemoglobin. Preparatory apnea can help us settle into the dive. A shallow dive can check equalization, rehearse technique, or simply tell us what kind of day we are having.
And this brings me back to what matters most:
What do I actually need before this dive, and what is the cheapest way to get it?
For a deep performance dive, I want to arrive ready without spending what I will need later. For technical work, a shallow dive can have a very clear purpose. For RV training, the progression itself can already be the warm-up.
And if I am doing a deep FRC dive simply because somebody once told me I need to “activate my blood shift”...
Well.
You already know how I feel about that one.
After all the reading, experimenting, questioning, and eventually changing my own approach, that is probably the simplest answer I can give.
If the warm-up cannot justify its cost, it has no place before the dive that matters.
Further Reading
If you want to understand what actually happens in your body during a dive and how to build your training around it, The Depth Collector: Book One explores CO₂ tolerance, hypoxia resistance, technique, anatomical adaptation, and mental control.
The Depth Collector: Book Two takes the next step, covering physical preparation, nutrition, recovery, safety, and training periodization.
Together, they provide a complete framework for freedivers who want to stop guessing and start training with purpose. Both books are available on Amazon in paperback, hardcover, and Kindle formats.
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