The Heart Rate of Breath-Hold Divers During Static Apnea, Effects of Competitive Stress
Authors: Peter Lindholm, Jan Nordh, Mats Gennser
DOI / Source: https://pubmed.ncbi.nlm.nih.gov/16716062/
Date: 01 April 2006
Reading level: Beginner
Why This Matters for Freedivers
If you’ve ever done a great static in training and then “mysteriously” underperformed in a comp (or even just in front of people), this paper explains why: competition stress can keep your heart rate higher right when you want it low. A higher heart rate early in the hold likely means you burn oxygen faster, and that can shorten your attempt or push you closer to LMC/blackout.
Synopsis
Static apnea is supposed to be the ultimate relaxation event: you float, you go quiet, your heart rate drops, and you let the dive response do its oxygen-saving thing. But competitions add a weird ingredient—pressure, attention, and nerves—and divers often report that they can’t reproduce their best training times when it “counts.”
This study looked at exactly that. The researchers measured heart rate in eight male competitors during the Swedish Championship in static apnea, and compared it to the same divers during a separate training session (control condition). Heart rate was recorded continuously using a Polar system while the divers did their warm-up apneas and then their main performance apnea, floating face-down in warm pool water in wetsuit and mask. The key point: the competition setup couldn’t be disturbed, so the measurements had to be simple and non-invasive—heart rate only.
The main finding was clear: heart rate was significantly higher during competition, both before the breath-hold and during the early part of the breath-hold. The difference was strongest in the first ~90 seconds of the apnea, then the heart rate patterns gradually converged as the hold went on. In other words, competitive stress seems to interfere most with the part of the static where you’re trying to “drop in” and settle into the easy phase.
One athlete in the study had loss of motor control (LMC) at the surface during the competition. The paper doesn’t claim heart rate alone caused that—hypoxia risk is multi-factorial—but it highlights a real safety implication: if stress raises heart rate and oxygen use early, you may arrive at the critical end of the apnea with less reserve than you expect.
A really useful idea in the discussion is that static has two recognizable phases: an early easy-going phase (calm, little urge to breathe) and a later struggle phase (contractions and growing drive to breathe). The authors suggest the stress difference may matter most in the early phase—when you’re trying to switch into low metabolism and strong bradycardia. Later, once the struggle phase takes over, both training and competition may be dominated by similar internal stress signals, which could explain why the heart rate difference shrinks.
Practical takeaway: your competition routine should be built around one goal—getting the nervous system to downshift quickly. That means fewer external stimuli, calmer preparation, and a warm-up strategy that’s familiar and repeatable. The “zone” isn’t just psychology here—it shows up as measurable physiology.
Abstract
This study measured heart rate in eight competitive breath-hold divers during a national static apnea competition and compared it to heart rate during a separate training session. During competition, divers showed a higher heart rate before the start and during the early part of the breath-hold, with the largest difference occurring within roughly the first 90 seconds. As the apnea continued, heart rate decreased and the gap between competition and training became smaller. The authors interpret the elevated early heart rate as an effect of competitive (mental) stress that may reduce oxygen-conserving benefits during apnea and could negatively affect performance and safety.