Lactate increases oxygen unloading of preconditioned blood from male elite breath-hold divers
Authors: Thomas Kjeld, Egon Godthaab Hansen, Henrik Christian Arendrup, Jens Højberg, Anders Nedergaard, Thomas Krag, John Vissing
DOI / Source: https://doi.org/10.14814/phy2.70698
Date: 28 November 2025
Reading level: Intermediate
Why This Matters for Freedivers
This study suggests lactate isn’t only “fatigue,” it may actually help your blood release oxygen more easily when oxygen is getting low — exactly the situation in late-phase apnea and deep ascents. It also hints that elite freedivers may be biologically tuned to handle lactate and hypoxia differently, which could partly explain why some divers stay functional at very low oxygen levels. Practically, it supports the idea that smart training can build “oxygen delivery under stress,” and that a bit of effort/lactate in warm-ups might sometimes be useful — but only within safe, controlled protocols.
Synopsis
Lactate is usually treated like a “fatigue by-product” — the stuff that builds up when you push hard. This paper flips that idea on its head and asks a pretty wild question: could lactate actually help you during intense hypoxia, by making it easier for your blood to let go of oxygen when tissues need it most?
The researchers focused on a concept called remote ischemic conditioning (RIC). In plain terms, it’s a short, controlled “stress” applied to a limb (like inflating a blood-pressure cuff hard for a few minutes, then releasing it, repeated in cycles). In some sports and medical research, RIC has been linked to better performance and protection against low-oxygen stress — but the exact “messenger” in the blood that carries this effect isn’t fully agreed on. One candidate is lactate.
They compared six elite male breath-hold divers with six aerobically fit controls matched for body size and VO₂max. Both groups did the RIC protocol (cuff inflation/deflation cycles). The divers also performed a max apnea (after warm-up apneas), and everyone did a VO₂max cycling test. They took arterial and venous blood samples at key moments and then did something clever: they added lactate to the blood in the lab (versus a placebo solution) and checked how the blood handled oxygen.
The key idea here is oxygen unloading — not just how much oxygen is in your blood, but how readily hemoglobin releases it to your tissues. They used a standard measure related to hemoglobin’s “grip” on oxygen (often discussed as shifts of the oxygen-hemoglobin curve). After RIC, adding lactate to the divers’ blood made it release oxygen more easily, while the same effect wasn’t seen in the controls. On top of that, the divers showed higher lactate dehydrogenase activity (especially forms linked to heart and red blood cells), which supports the idea that elite breath-hold divers may be tuned to use and process lactate differently under low-oxygen stress — a bit like what we see in diving mammals.
The bottom line: in these elite divers, lactate looks less like “waste” and more like a potential tool — helping oxygen get delivered where it’s needed during and after stressful hypoxic exposures. It doesn’t mean you should chase lactate blindly, but it does suggest the freediver body may be adapted to turn “burn” into “benefit” in very specific contexts.
Abstract
Physical performance can be improved in aerobic athletes and breath-hold divers (BHD) by limb exposure to repetitive ischemia: remote ischemic conditioning (RIC). RIC protects against cardiac ischemia, and its blood-borne transferable substrate could be lactate. Accordingly, lactate added to whale blood increases oxygen unloading and adult seals possess higher cardiac lactate dehydrogenase activity (LDHa) than terrestrial mammals. Because BHD and adult diving mammals share adaptations to hypoxia, including lactate metabolization during apnea, we hypothesized that BHD compared to BMI/VO₂max-matched aerobic controls have higher LDHa and lactate added to blood from BHD unloads oxygen more efficiently. Six BHD and six matched aerobic controls underwent RIC: three cycles of 5-min inflation and 4-min deflation of a blood pressure cuff on the dominant arm, maximum apnea after three submaximal apneas (BHD only), and a VO₂max-test. Blood samples were collected from the nondominant radial artery and the vena basilica of the dominant arm at rest, before termination of the three interventions, and for LDHa. Blood gases were compared to samples added lactate or placebo suspension. BHD had ~30% higher cardiac/erythrocyte LDHa compared to controls (p<0.05). Lactate added to arterial blood from BHD after RIC increased oxygen unloading (p<0.05). PaO₂ decreased ~66% during apnea (375±49 s; p<0.001; BHD only). We conclude that (1) erythrocyte- and cardiac-LDHa is higher in BHD compared to matched controls, and (2) lactate facilitates oxygen unloading in blood from BHD after RIC, similar to diving mammals.