The Role of Training in the Development of Adaptive Mechanisms in Freedivers
Authors: Andrzej Ostrowski, Marek Strzała, Arkadiusz Stanula, Mirosław Juszkiewicz, Wanda Pilch, Adam Maszczyk
DOI / Source: https://doi.org/10.2478/v10078-012-0036-2
Date: 01 May 2012
Reading level: Intermediate
Why This Matters for Freedivers
This paper connects the classic “diving reflex” to what training actually changes over time. It explains why experienced divers often feel calmer, burn oxygen more slowly, and tolerate the struggle phase better—and it also highlights the safety edge: these same adaptations can let you push deeper/longer, which makes good supervision and conservative decision-making even more important.
Synopsis
Freediving looks simple from the outside—hold your breath and go. But inside the body, it’s a controlled crisis: oxygen is dropping, CO₂ is rising, and (in depth diving) pressure changes can push physiology in surprising directions. This review explains the main “adaptive mechanisms” that protect a freediver during apnea, and how specialized training appears to strengthen them.
The paper starts with the two big stressors in freediving: - Time underwater → gradually increasing hypoxia (low O₂) and hypercapnia (high CO₂). - Depth → hydrostatic pressure changes that can alter gas pressures and raise extra risks during ascent.
From there it walks through the core package often called the diving response: - Bradycardia (heart rate slows) to reduce oxygen use by the heart. - Peripheral vasoconstriction (blood vessels in limbs tighten) so less oxygen is “spent” in muscles and skin. - Blood centralization (more blood is kept in the chest and core) to prioritize the brain and heart. - Hormonal support (stress hormones/catecholamines) that help drive and stabilize these responses.
A big theme is that training doesn’t just make you “tougher”—it may make these reflexes more efficient and better timed. The review describes how, with repeated apnea exposure, divers often show a stronger autonomic response: higher sympathetic drive during falling oxygen saturation, higher blood pressure support, and a clearer shift of blood toward essential organs. It also explains why the brain can stay “okay” longer than you’d expect: rising CO₂ increases cerebral blood flow, and the Bohr effect helps oxygen unload where it’s needed.
One of the most interesting adaptations discussed is the spleen effect. The spleen can contract during apnea and release stored red blood cells into circulation, slightly increasing hemoglobin and hematocrit for a short time. The review links this to why “warm-up apneas” can help performance in repeated dives: after a few apneas, the spleen response may be near its maximum, giving you a temporary boost in oxygen-carrying capacity and CO₂ buffering.
The paper also covers the blood shift concept for depth: as pressure compresses the lungs, blood (and sometimes abdominal organs shifting upward) can help “fill” the chest space and protect against lung squeeze beyond what simple lung-volume math would predict.
On the “limits” side, it explains the breakpoint and struggle phase in practical terms: involuntary breathing movements ramp up as CO₂ rises and oxygen falls. Trained divers don’t remove the struggle phase—they tend to tolerate it better and manage it with relaxation, technique, and experience.
Finally, the review touches on longer-term training effects that have been reported in the literature: improved breath-hold performance, changes in blood variables (including EPO-related discussions), and in some studies a pattern of reduced lactate buildup and reduced oxidative stress after apnea training—possibly because less oxygen is delivered to working muscles during apnea and because repeated exposure changes how the body handles re-oxygenation.
Overall, it’s a broad “how the machine works” paper: it doesn’t claim one magic adaptation explains everything, but it gives you a clear map of what training is trying to develop—oxygen saving, smart blood distribution, and better tolerance of the stress signals that normally force breathing to restart.
Abstract
Freediving involves prolonged breath-holding and exposure to changing pressure, creating progressive hypoxia and hypercapnia and increasing the risk of loss of consciousness without immediate assistance. This review discusses how specialized training may develop adaptive cardio-respiratory mechanisms that improve oxygen management during apnea, including bradycardia, increased blood pressure, peripheral vasoconstriction, and blood centralization toward the brain and heart. These responses are supported by hormonal reactions involving catecholamines and the spleen effect, which can transiently increase circulating red blood cells. The paper summarizes proposed training-related adaptations relevant to performance and safety in breath-hold diving.