The Oxygen-Conserving Potential of the Diving Response, A Kinetic-Based Analysis

Authors: Guillaume Costalat, Jeremy Coquart, Ingrid Castres, Fabrice Joulia, Olivier Sirost, Eric Clua, Frédéric Lemaître
DOI / Source: https://doi.org/10.1080/02640414.2016.1183809
Date: 11 May 2016

Reading level: Intermediate

Why This Matters for Freedivers

Freedivers often talk about the “diving reflex” like it’s one smooth, gradual slowdown. This study suggests that for trained divers there may be a mid-apnea switch where the body suddenly gets more serious about saving oxygen—slowing the heart more and reducing blood flow to working muscles. If that’s real, it helps explain why good divers can feel “fine… fine… then suddenly very different,” and why pacing and effort choice can make or break a dive.

Synopsis

This paper asks a simple but powerful question: do trained breath-hold divers save oxygen more efficiently than non-divers—and if yes, can we see when and how that happens during a breath-hold?

To test this, the researchers compared two groups: trained breath-hold divers and non-divers. Everyone performed a maximal dynamic breath-hold while cycling at a light-to-moderate workload, with cold face immersion (a strong trigger for the diving response). Throughout the breath-hold they continuously measured heart variables (heart rate, stroke volume, cardiac output), finger oxygen saturation (SpO₂), and muscle oxygenation in the thigh using NIRS (which estimates changes in oxygenated and deoxygenated blood signals in the muscle).

Both groups showed the expected “diving response” pattern: heart rate fell during the breath-hold and SpO₂ dropped toward the end. But the trained divers did something different. Their heart-rate drop was not just a smooth line downward. Instead, around the middle of the breath-hold, their heart-rate curve showed a clear “bend” where the decline became much steeper—what the authors describe as an oxygen-conserving breaking point. In simple terms: halfway through, the divers’ bodies seemed to shift into a more aggressive oxygen-saving mode.

What makes this more interesting is what happened in the muscles at roughly the same time. The NIRS data suggested that trained divers had a smaller rise in deoxygenated signal than non-divers toward the end, and they also showed a drop in total blood signal in the working muscle—consistent with reduced muscle blood flow. That fits the classic oxygen-saving story: keep blood and oxygen for the organs that matter most (brain and heart), and restrict flow to working limb muscles when oxygen starts getting scarce.

The study also found higher post-breath-hold blood lactate in the trained divers, which supports the idea that if muscle blood flow is being restricted, the muscle may lean more on anaerobic metabolism (more “glycolysis”) during that breath-hold exercise.

A key point: the “breaking point” happened at a similar oxygen saturation level in both groups (around the mid-90s), but only trained divers showed the extra cardiac + peripheral shift. That suggests training may not just increase tolerance—it may change how the body responds under stress, possibly through stronger reflex control of heart rate and blood vessel constriction.

Overall, the paper argues that trained divers don’t just hold their breath longer—they may activate a more effective oxygen-conservation strategy mid-breath-hold, combining a stronger bradycardia pattern with reduced blood delivery to working muscle.

Abstract

This study compared trained breath-hold divers with non-divers during a simulated dynamic breath-hold with cold face immersion to evaluate how effectively the diving response conserves oxygen. Heart variables, finger oxygen saturation, and thigh muscle oxygenation were recorded continuously. Trained divers showed a distinct mid-breath-hold change in heart-rate behavior followed by a stronger late bradycardia, alongside signs consistent with reduced oxygen extraction and reduced blood volume/flow in the working muscle near the end of the breath-hold. These combined cardiac and peripheral adjustments support the idea that trained divers can increase oxygen-conserving efficiency, and the results provide evidence for an “oxygen-conserving breaking point” during the human diving response.

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