The Limits of Breath Holding
Authors: Michael J. Parkes
DOI / Source: https://www.scientificamerican.com/article/the-limits-of-breath-holding/
Date: April 2012
Reading level: Beginner
Why This Matters for Freedivers
Most freedivers think the “limit” is simply running out of oxygen. This article explains why you usually quit long before that — because your body’s breathing machinery (especially the diaphragm) starts sending escalating “this is not okay” signals. Understanding that difference helps you train smarter: not just more oxygen, but better control of discomfort, pacing, and safety choices (especially around hyperventilation).
Synopsis
Try holding your breath right now. What stops you is rarely “oxygen is gone.” For most people, the stop button is break point: the moment the urge to breathe becomes so strong that you can’t voluntarily resist it. In this Scientific American article, physiologist Michael J. Parkes explores why break point happens — and why it’s surprisingly hard for science to pin down.
A key puzzle is this: your lungs often contain enough oxygen to last longer than the typical breath-hold, and carbon dioxide doesn’t reach instantly toxic levels either. Yet most people feel forced to breathe much earlier. One obvious guess is that special sensors monitor oxygen/CO₂ and “protect you” by triggering breathing. But decades of research have complicated that idea.
The article describes how researchers tested several likely candidates and found they don’t explain break point on their own. People without normal lung sensory feedback (for example after certain surgeries) don’t suddenly become breath-holding superhumans. And even when chemoreceptor input is reduced, people still reach a break point rather than calmly holding their breath until they pass out. Even more strangely, classic experiments showed that after one maximal breath-hold, people can sometimes hold again immediately — even as their blood gases get progressively worse. That suggests break point isn’t just a simple “gas threshold” alarm.
So what is it? The strongest working explanation is the diaphragm.
During a breath-hold at full lungs, you’re not just “not breathing” — you’re actively preventing the normal breathing rhythm from expressing itself. The brain’s respiratory rhythm keeps ticking in the background, and the diaphragm is held in an unusual, sustained state. The article explains evidence that this prolonged diaphragm contraction likely sends sensory signals to the brain: about effort, stretch, and biochemical stress as oxygen drops and CO₂ rises. Early on those signals feel like discomfort. Later they become intolerable, and the brain “wins the argument” by forcing breathing to restart.
Some of the most dramatic (and now largely unrepeatable) experiments involved temporarily paralyzing muscles. When diaphragm feedback was removed, volunteers reported far less distress and could tolerate much longer “breath-hold” periods — until clinicians stopped the test because CO₂ became dangerously high. That supports the idea that break point is strongly tied to diaphragm sensations rather than a simple oxygen cliff.
The article closes with two practical themes for freedivers. First, elite breath-holders extend time using strategies like extreme relaxation, maximising lung inflation (sometimes with advanced techniques), and manipulating oxygen and CO₂ — but these come with serious risks. Second, understanding break point isn’t just sport science; it matters in medicine (e.g., breath-hold radiotherapy) and in safety contexts where stress, exertion, and restraint can sharply shorten breath-hold tolerance and destabilise the heart.
Abstract
This article explains why humans usually feel compelled to breathe long before oxygen stores are fully exhausted. Research suggests that break point is not determined solely by lung volume sensors or by fixed oxygen/CO₂ thresholds. The best current explanation is that during voluntary breath holding, the diaphragm is held in a sustained contracted state while the brain’s respiratory rhythm persists, and escalating sensory signals from the diaphragm become intolerable, forcing breathing to resume. The piece also reviews how training, relaxation, and gas manipulation can extend breath-holding, and why these methods carry important safety implications.