Who writes this
Jan Luther. I am a keen amateur freediver, and I built Apnea Trainer — maintained since 2010, on iPhone, Apple Watch and Android. I train and dive myself, and that is exactly where this blog comes from: the scene is full of claims nobody ever checked. Here they get held up against what was actually measured.
Why this blog exists
Breath-hold training carries more folklore than most sports. The "ideal 40-second BOLT score" has no controlled study behind it. Two weeks of holds do not give you an altitude-training blood profile — that was measured, and nothing moved. You cannot stretch your lungs bigger. Each of those is an article here, and each one ends where the measurements end rather than where the story would be nicer.
How the sources are chosen
Every figure, percentage and time span in an article is tied to a named study, with the journal, the year and a link to the abstract — the PubMed page wherever one exists, because that is the version you can actually open. Where a claim is popular in the scene but has thin or no evidence behind it, the article says so instead of quietly repeating it. If a study cannot be linked, the claim does not go in.
How articles are kept current
When an article is revised, the links are opened again and checked against what the sources actually say, and the date on the article is updated. Corrections are made in place — if something here is wrong, tell me and it gets fixed.
Safety and medical advice
Training articles are education, not medical advice, and no article replaces in-water instruction from a qualified freediving instructor. Breath-hold training carries real risk, especially in water. Never hold your breath in or near water without a trained buddy watching you. If you are pregnant, have a heart or lung condition, high blood pressure, epilepsy, or take medication, talk to your doctor before you start.
Contact and corrections
Reach me through the contact details in the imprint. Corrections are welcome and get made in the article itself, not in a footnote.