Do Elite Breath Hold Divers Suffer From Mild Short Term Memory Impairments?
Authors: François Billaut, Patrice Gueit, Sylvane Faure, Guillaume Costalat, Frédéric Lemaître
DOI / Source: https://doi.org/10.1139/apnm-2017-0245
Date: October 2017
Reading level: Intermediate
Why This Matters for Freedivers
This study is a useful reality check: it doesn’t say freediving “ruins your brain,” but it suggests that repeatedly pushing maximal apneas for years might be associated with small, specific changes in executive control in some elite divers. Practically, it supports a conservative training culture: don’t normalize frequent max attempts, minimize hypoxic events, and treat brain health like you treat ears and lungs — something you protect with smart progression and recovery.
Synopsis
Freedivers love the idea that training makes you “stronger” in every way — but this paper asks a more uncomfortable question: if elite divers repeatedly push into very low oxygen, does that leave a small “fingerprint” on the brain over time? The researchers compared three groups of men matched for age and body size: 12 elite breath-hold divers, 12 novice breath-hold divers, and 12 non-diving controls. The elite group averaged a best static apnea around 371 seconds (just over 6 minutes) with about 105 months of apnea experience; novices averaged about 243 seconds with ~9 months of experience. 
Everyone completed a battery of standard cognitive tests: memory tasks (word lists, Rey figure recall), working memory (letter/number sequencing), reaction time tasks, and a classic “mental control under distraction” test: the Stroop test. The Stroop is basically: can you ignore an automatic response (reading the word) and instead do the harder thing (say the ink color). It’s a good measure of attention control and short-term “mental braking.” 
The reassuring part: across most memory and attention tests, there were no pathological scores and no clear differences between groups. The interesting part: the elite divers were slower on the Stroop interference card than novices and controls, and their interference performance was related to how extreme their freediving was. The time to complete the interference card correlated with best static apnea time (r ≈ 0.73) and even more strongly with years of breath-hold training (r ≈ 0.79). In simple terms, the more “elite” and long-trained the diver, the more they tended to show a small drop in this specific executive-control measure. The authors interpret this as a possible sign of mild, persistent impairment in short-term executive/working control, potentially linked to years of repeated severe hypoxia (and possibly hypercapnia), even if the effect is subtle and not seen across all tests.
Abstract
Repeated apneas are associated with severe hypoxemia that may ultimately lead to loss of consciousness in some breath-hold divers. Despite increasing number of practitioners, the relationship between apnea-induced hypoxia and neurocognitive functions is still poorly understood in the sport of free diving. To shed light onto this phenomenon, we examined the impact of long- term breath-hold diving training on attentional processing, short-term memory, and long-term mnesic and executive functions. Thirty-six men matched for age, height and weight were separated into three groups [12 elite breath-hold divers (EBHD, mean static apnea best time 371 sec, 105 months mean apnea experience); 12 novice breath-hold divers (NBHD, mean best time 243 sec, 8.75 months mean apnea experience); and 12 physical education students with no breath-hold diving experience (CRTL)], and performed varied written and computerized neuropsychological tasks. Compared with the two other groups, EBHD were slower to complete the interference card during a Stroop test (F(1,33)=4.70, p<0.05), and presented more errors on the interference card (F(1,33)=2.96, p<0.05) and a lower total interference score (F(1,33)=5.64, p<0.05). The time to complete the interference card test was positively correlated with maximal static apnea duration (r=0.73, p<0.05) and the number of years of breath-hold diving training (r=0.79, p<0.001). These findings suggest that breath-hold diving training over several years may cause mild, but persistent, short-term memory impairments.