Human Breath-Hold Diving Ability and the Underlying Physiology
Authors: Erika Schagatay
DOI / Source: https://www.scopus.com/record/display.url?origin=inward&partnerID=40&eid=2-s2.0-85012195534
Date: 01 January 2014
Reading level: Beginner
Why This Matters for Freedivers
This is a big-picture “how freediving works” map: it connects the dive response, spleen contraction, lung volume tricks, equalisation skills, and training effects into one story. It’s especially useful when you want to explain why certain training methods help (and where the real limits and risks start, like extreme depth and decompression problems).
Synopsis
This paper is a wide, readable tour of what makes humans surprisingly good breath-hold divers—and what physiological “tools” we use to do it. It compares three types of freedivers: recreational divers (a few meters for fun), traditional harvest divers (daily repetitive dives for food), and elite competitors who push single-dive limits in time, distance, and depth.
Humans as serious breath-hold divers
Schagatay argues that humans show breath-hold abilities that are unusually strong for a land mammal. Traditional harvest divers (like Japan’s Ama and Southeast Asian sea nomads) may spend hours in the water and rack up very large total underwater time each day through many short dives with short recoveries. Competitive divers, on the other hand, focus on one maximum attempt—static times over 10 minutes and deep dives beyond 100 m have been achieved in modern sport.
The key “oxygen management” systems
The paper breaks down several systems that work together:
1) The diving response (diving reflex).
Breath-holding plus face cooling triggers a shift that helps conserve oxygen: heart rate drops and blood vessels constrict in less-critical tissues, sending relatively more blood to the brain and heart (and to working muscles when needed). Training can make this response stronger, and in trained divers the heart-rate reduction can reach levels similar to semi-aquatic mammals.
2) The spleen response (extra red blood cells).
Humans can temporarily boost oxygen-carrying capacity by contracting the spleen during repeated apneas. The spleen releases stored red blood cells, increasing hemoglobin/hematocrit for a short window, which can prolong apnea and improve recovery between dives. The effect builds across several breath-holds and fades back toward baseline after roughly 10 minutes without apnea.
3) Gas storage and lung volume.
Humans rely heavily on lung oxygen stores, especially compared with deep-diving marine mammals that carry more oxygen in blood and muscle. Many traditional divers have relatively large lungs, and elite competitors often push this further with lung training and techniques like “packing” (buccal pumping) to increase starting lung volume. Bigger lung volumes can increase oxygen storage and help with depth by delaying the point where lungs compress toward residual volume.
Equalisation and “deep technique”
A major limiter in deep freediving is not just oxygen—it’s managing pressure in air spaces. The paper describes how deep divers use advanced equalisation strategies like “mouthfill” once lung air can’t be easily moved at depth. This requires fine control of soft palate, tongue, and airway “valves,” and it becomes critical beyond roughly 25–40 m for many divers.
Performance limits and risks
Schagatay discusses how self-propelled competition disciplines are relatively safe when done with strong safety protocols, even though hypoxic blackouts can occur near the surface. But when divers use assisted techniques to reach extreme depths (sled descent and/or rapid ascent devices), risks climb sharply—including serious decompression-related injuries, which have also been observed in marine mammals under certain conditions.
An evolutionary angle
The paper also explores an evolutionary hypothesis: humans share a surprising list of traits with semi-aquatic animals (streamlined form, lack of fur, subcutaneous fat layer, strong diving response, good breath control, adaptable underwater vision), and it raises the possibility that past selective pressures near shorelines could have shaped some of these features. Whether or not you buy the evolutionary argument, the paper’s main value for divers is that it ties together the mechanisms behind human freediving capacity in a coherent, real-world way.
Abstract
Humans freedive for recreation, food, and for records, displaying an ability superior to any other known terrestrial mammal. Harvest divers may spend up to 5 h daily submerged, and competitive deep divers may swim down to depths beyond 100 m – and up again – on one breath. This is paralleled only by aquatic and semi-aquatic mammals. In all air breathers, the ability to breath-hold dive is set by a number of physiological factors. Some of these have been extensively studied, like the ‘diving response,’ which diverts blood to the brain, heart and working muscles, while less sensitive organs can rely on anaerobic metabolism. The diving response is effectively triggered in trained human divers and may reduce the heart rate by 50% – similar to the response in semi-aquatic mammals, and it has been shown to conserve oxygen and prolong apneic duration. More recently, a spleen response during diving was described in humans resembling that found in seals. The spleen ejects its stored reserve supply of red blood cells into the circulation, elevating hematocrit, and thereby the oxygen carrying capacity, which also increases apneic duration. Other features not typical of terrestrial mammals, such as: naked skin with a continuous layer of subcutaneous fat; under water vision; effective locomotion in water; large flexible lungs; an ability to equalize ears and sinuses; efficient voluntary respiratory control and vocal communication; a long lifespan; and a large brain, are shared by many species with a semi-aquatic evolutionary history and are also shared by Man. This would seem to suggest a period of evolutionary pressure from life involving swimming and diving in human prehistory.