29 Minutes Holding One’s Breath – How Is That Possible?

Recently, Croatian freediver Vitomir Maričić set a new world record in static apnea: he held his breath for 29 minutes and 3 seconds—a feat that seems almost superhuman to outsiders. Physiologically, it can be explained, but the mental discipline behind it remains extraordinary.

The world record

On 14 June 2025, Maričić dived into a 3-metre-deep pool at the Hotel Bristol in Opatija, Croatia. In front of five official judges and around 100 spectators, he lay calmly on his back at the bottom of the pool with his hands clasped behind his head.

As permitted by Guinness guidelines, he prepared himself by breathing pure oxygen (preoxygenation). After resurfacing, he reported: ‘From the 20th minute onwards, it became easier mentally, although physically it got worse and worse – especially because of the strong diaphragmatic contractions. But giving up was out of the question.’ He attributed his success to the support of his team, family and friends.

For comparison: the official AIDA world record in static apnea using normal air has stood since 2013 at 11:35 minutes (Stéphane Mifsud). Maričić’s personal AIDA best time is 10:08 minutes.

Pre-oxygenation – Charging the Reserves

With normal breathing, the lungs, blood, and tissue provide only about 300 ml of oxygen—barely enough for more than one minute of breath-holding.

But after pre-oxygenation with 100% O₂, the lungs become “charged” with oxygen. Along with reserves in blood and tissue stores, this gives access to several liters of O₂.

This method is also used in medicine—for instance in anesthesia, to ensure enough time for intubation before resuming ventilation after anesthesia-induced apnea. It’s also applied in radiotherapy (e.g., for breast cancer) so that patients can hold their breath for longer during treatment. Even untrained individuals can achieve several minutes with pure oxygen breathing—note, without deep inhalations, but just calmly at rest.

Die Alveolargleichung

The basis for the physiological explanation is the alveolar equation, which can be used to calculate the alveolar oxygen partial pressure PAO₂. Since this cannot be measured directly, it is calculated from the fraction of inhaled O₂ (FIO₂, e.g. air 0.21), ambient pressure, water vapour pressure, the arterial CO₂ partial pressure (PaCO₂) and the respiratory quotient (RQ = ratio of CO₂ output to O₂ intake). As a medical professional, I use mm Hg as the unit of measurement instead of bar, whereby the ambient pressure of 1 bar corresponds to 760 mm Hg. The vapour pressure (47 mm Hg) must be subtracted from this because the air in the alveoli is 100% saturated with vapour. With normal breathing (FiO₂ = 0.21, PaCO₂ = 40 mmHg, RQ = 0.8), the result is:

This value means that at an ambient pressure of 1 bar, the alveolar oxygen fraction is approximately 100/760 = 0.13. However, not all of this is fully available, as the O₂ partial pressure must not fall below a critical threshold of approximately 30 mmHg – otherwise there is a risk of unconsciousness. The fraction that can actually be used is therefore (100−30)/760 ≈ 0.09.

If an average person takes a full breath before holding their breath, a lung with a volume of 6 litres contains 540 ml of available oxygen (6 litres x 0.09). With an oxygen consumption of 250 ml/min (corresponding to the theoretical resting metabolism of a 70 kg person), this reserve would be used up after 2 minutes and 10 seconds.

This is the first key to apnoea diving: only those who reduce their oxygen consumption to an extreme level can truly extend their reserves. Maximum physical and mental relaxation is therefore essential – for Maričić, this was the basis of his record.

How does the calculation change with pure O₂ breathing over 10 minutes? (Guinness World Record attempts allow up to 30 minutes.) In this case, the lungs are almost completely filled with oxygen. The alveolar O₂ partial pressure rises to:

Assuming a lung volume of 6 litres and a critical blackout threshold of 30 mmHg, this results in an oxygen quantity of:

This is theoretically enough for 20 minutes. Performance artists and stuntmen actually use this to awe audiences. But Maričić's 29 minutes is still a long way off.

Lung packing

This is where the special technique of elite divers comes into play: lung packing. Anyone who watches free divers descend will notice the bizarre movements of glossopharyngeal breathing. By contracting the throat muscles, they press additional air into the lungs, increasing lung volume to 8 to 9 litres.

Combined with preoxygenation, this dramatically increases the O₂ reserve. Assuming a volume of 9 litres and a critical blackout threshold of 30 mmHg, the result is:

At a consumption rate of 250 ml/min, this reserve is theoretically sufficient for 30 minutes – exactly the order of magnitude of Maričić's record.

This partly explains the world record. But the real difficulties only begin with the opponent: CO₂.

CO₂ – the real opponent

Almost every molecule of oxygen consumed in metabolism is converted into carbon dioxide (CO₂). Since this is not exhaled during apnoea, the partial pressure of CO₂ in the blood inevitably rises by about 3–6 mm Hg per minute. The higher the O₂ consumption, the greater this increase – another reason why complete relaxation is so important for freedivers.

The problem: CO₂ is the body's strongest respiratory stimulus. While a low O₂ content only triggers unconsciousness at a relatively late stage, the respiratory centre reacts early on to rising CO₂ concentrations in order to protect the sensitive acid-base balance in the blood. Through carbonic acid formation, CO₂ directly leads to acidosis (over-acidification), which can only be corrected by increased exhalation. This is why the organism has given CO₂ such a dominant respiratory stimulus.

• Untrained individuals feel a massive urge to breathe at a PaCO₂ of around 50–55 mmHg.

• Trained freedivers can tolerate values of 60–65 mmHg and above.

This makes it clear that it is not the lack of oxygen that ends apnoea, but the respiratory stimulus caused by CO₂. Long before the O₂ reserve is exhausted, CO₂ normally forces breathing. This also protects the body from oxygen deficiency.

Elite divers like Maričić are able to delay this urge to breathe to such an extent that the CO₂ limit and O₂ limit almost coincide – making apnoea times of around 29 minutes possible.

How is such a high CO₂ tolerance achieved?

1. Increased buffer capacity: Training improves the blood's ability to absorb acid loads. CO₂ is better neutralised chemically, so that PaCO₂ rises more slowly.

   
   

2. Weakened chemoreceptor sensitivity: Many years of apnoea training lead to neurophysiological desensitisation of the central and peripheral receptors – the respiratory stimulus sets in later.

   
   

3. Genetic predisposition: Some people (‘CO₂ retainers’) naturally have a weaker respiratory response to CO₂. It is believed that they are more common than average among elite divers. However, this is difficult to prove, as it is not possible to distinguish between congenital and trained CO₂ retention.

   
   

4. Mental discipline: The respiratory stimulus is not only a physiological challenge, but also a psychological one. Elite freedivers train specifically to endure the increasingly violent diaphragmatic contractions and not to give in.

Willpower as the final hurdle

In the final minutes, Maričić also suffered from a drastic increase in respiratory stimulation. He himself reported massive, involuntary diaphragmatic contractions in the last minutes of his record attempt. Only by consistently suppressing this urge was he able to continue the apnoea. The knowledge that he was not in immediate danger of hypoxia thanks to pre-oxygenation certainly helped him – but the mental strength to resist this overwhelming impulse remains extraordinary.