Changes in hormones after apneic hypoxia/hypercapnia - An investigation in voluntary apnea divers
Authors: R.C. Dolscheid-Pommerich, B. Stoffel-Wagnera, R. Fimmers, L. Eichhorn
DOI / Source: https://doi.org/10.1016/j.resp.2022.103845
Date: 13 January 2022
Reading level: Intermediate
Why This Matters for Freedivers
A single hard breath-hold can trigger a real hormonal stress response that lasts beyond the session, which may help explain why people sometimes feel “wired then drained” after intense apnea training. Practically, it supports smart programming: avoid stacking maximal efforts too often, prioritize recovery, and take persistent fatigue or unusual symptoms seriously—because even “dry apnea” can stress the system.
Synopsis
Freedivers often think about oxygen, CO₂, and heart rate — but there’s another system reacting quietly in the background: your hormones. This study asked a simple question: can one single maximal breath-hold (done “dry,” lying down, not in water) shift stress hormones and sex hormones in trained apnea divers? To test it, the researchers recruited 10 trained apnea divers (8 men, 2 women) and drew blood before apnea, immediately after, 30 minutes after, and 4 hours after. They measured a wide panel of hormones with modern lab methods (LC–MS/MS for steroid hormones, immunoassays for LH/FSH). 
The pattern they found is pretty clear and very “body makes sense” once you see it. After the maximal apnea, several stress/adrenal hormones rose and peaked around 30 minutes after the breath-hold — including cortisol and other adrenal steroids (like corticosterone, DHEA, androstenedione, 17-OH-progesterone, and progesterone). By 4 hours, many of these had dropped back toward baseline (some even below). At the same time, some sex-related hormones showed a different trend: testosterone (and also DHT) tended to be lower at 4 hours, while LH and FSH (the pituitary “control signals”) did not change significantly. In plain terms: one hard apnea looked like a short, real stress event for the body — you get a temporary adrenal “stress surge,” and later you may see a dip in some sex steroids without the brain’s gonadotropin signals obviously shifting. 
The authors also emphasize safety and context: this was done under strict supervision, and these results are in trained divers, so you shouldn’t assume the same response in beginners. But as a model, it’s useful because it isolates the effects of apnea-related hypoxia/hypercapnia from cold water, pressure, and exertion — showing that the breath-hold itself can be enough to move hormones measurably for hours.
Abstract
Background: Prolonged apnea is characterized by hypoxia/hypercapnia. Hypoxia can be associated with hormonal dysfunction. We raised the question as to whether steroid hormonal and gonadotropin levels could be influenced by short-term hypoxia/hypercapnia in a model of dry apnea in trained apnea divers. Methods: Adrenal, sex steroid and pituitary hormones were measured in ten trained voluntary apnea divers before, immediately after, 0.5 h and 4 h after a maximal breath-hold. Apnea was carried out under dry conditions.
Results: Corticosterone, progesterone, cortisol, 17− OH-progesterone, dehydroepiandrosterone and androstenedione showed a significant continuous increase with a maximum at 0.5 h after apnea, followed by a decrease back to or below baseline at 4 h after apnea. Testosterone, estradiol, cortisone and dihydrotestosterone showed a decrease 4 h after apnea. Dehydroepiandrosteronesulfate, luteinizing hormone (LH) and follicle stimulating hormone (FSH) showed no significant changes.
Conclusion: Even a single apnea resulted in two different patterns of hormone response to apnea, with increased adrenal and reduced sex steroid levels, while LH/FSH showed no clear kinetic reaction. Apnea divers might be a suitable clinical model for hypoxic disease.