Features of Gas Exchange in an Advanced-Level Freediver During Monofin Practice in a Pool
Authors: Natalia Molchanova, Vitaly Rybakov, Eugene Kalinin, Anna Kamenshikova
DOI / Source: https://doi.org/10.31236/osf.io/8jnbr
Date: 2013
Reading level: Intermediate
Why This Matters for Freedivers
This paper turns the “feel” of a pool dynamic session into real numbers: it shows how oxygen drops and CO₂ rises after different types of monofin training, and why the hardest part may not show up on your very first breath after surfacing. It also gives practical training guidance (interval vs continuous) tied to percentages of personal best, which is useful for planning safer sessions and understanding when you’re drifting into blackout-risk territory.
Synopsis
Most freedivers know dynamic apnea in the pool creates both hypoxia (low oxygen) and hypercapnia (high CO₂), but it’s surprisingly rare to see actual measurements of what the lungs are “putting out” after different training styles. This study followed an advanced freediver during monofin pool training and analyzed end-tidal gases (the oxygen and CO₂ in the air coming from the deepest part of the lungs) during recovery breathing after dives.
The subject was Alexey Molchanov (26 years old at the time, highly trained, personal best 250 m). He performed two main types of sessions: (1) continuous dives of 50, 100, 150, and 200 m with full recovery between, and (2) an interval set of 8 × 50 m with short rests (only five breaths). After each surfacing, he breathed through a gas-analysis mask starting from the first exhalation so the researchers could track how PetO₂ fell and PetCO₂ rose.
A key practical insight is that the first breath after surfacing doesn’t always show the “worst” values. Because of dead space in the airways, the strongest signal often appears after 2–3 breathing cycles, which matters if you’re judging how stressed you are based on how you feel immediately. The longer the continuous dive, the lower oxygen tended to be and the higher CO₂ tended to be during recovery—except for a 100 m “warm-up effect” that may have triggered protective mechanisms.
The 200 m effort (about 80% of personal best) was the big warning: it produced values consistent with acute hypoxia and acute hypercapnia, and the paper argues that distances above ~70% of personal best carry a real blackout risk and should not be repeated in a session—only attempted once, and only with a trained safety buddy. In contrast, interval training with shorter distances (roughly 20–40% of personal best) created moderate hypoxia with strong CO₂ load, which the authors describe as useful for building CO₂ tolerance and base conditioning, but not necessarily the best way to push maximum performance right before competition.
Abstract
During a monofin freedive in a pool an athlete goes into hypercapnia and hypoxia, which limits performance. During breath-holds the air stored in the lungs and airways changes its composition, but these changes are poorly studied in advanced freedivers. We analyzed the end-tidal air of an advanced-level freediver during pool training. Continuous freedives under 60% of personal best, or interval series with each dive under 20–40% of personal best, lead to moderate hypoxia and acute hypercapnia and are suitable for base training periods, increasing tolerance to CO₂ (though this will not directly improve athletic performance). For pre-competitive training periods for experienced freedivers we recommend continuous one-time dives (with a safety buddy) at distances over 70% of personal best.