Attenuation Of The Diving Reflex In Man By Mental Stimulation
Authors: Alvin Ross & Andrew Steptoe
DOI / Source: https://doi.org/10.1113/jphysiol.1980.sp013250
Date: 17 July 1979
Reading level: Beginner
Why This Matters for Freedivers
This supports a core training lesson: relaxation isn’t just psychological — it changes physiology. If you’re mentally stressed, overthinking, or “doing mental maths” during a dive, you may get less of the heart-rate-slowing benefit of the diving reflex, which can affect comfort and oxygen use. It’s a good reason to build routines that keep the mind simple and calm before and during breath-holds, especially in cold water.
Synopsis
Most freedivers learn early that putting your face in cold water and holding your breath tends to slow your heart rate — the classic “diving reflex.” But here’s the twist this paper explores: your brain can turn that reflex up or down. The researchers tested whether doing a mentally demanding task (mental arithmetic) changes how much the heart rate slows during a one-minute breath-hold, both in air and with face immersion in cold water (~15°C). 
They ran 12 short trials per person: breath-holds with and without face immersion, and each of those either with mental arithmetic (adding/subtracting numbers during the breath-hold) or with a “distraction” control (listening to prose being read). The big finding is very intuitive for divers once you see it: cold-water face immersion produced a much stronger bradycardia than breath-holding in air, but mental arithmetic reduced (attenuated) that bradycardia in both situations. In other words, when the mind is “working hard,” the heart doesn’t slow down as much as it normally would during apnea/face immersion. Listening to prose did not change the response, which suggests it’s not just “being distracted,” but specifically mental challenge/stress that blunts the reflex. 
Why might this happen? The authors argue that a demanding cognitive task likely changes the balance of your autonomic nervous system — pushing toward more “alert” activation and/or reducing the vagal (parasympathetic) brake that normally slows the heart. The practical takeaway is simple: the diving reflex isn’t a fixed on/off switch. It’s a reflex, yes — but it’s also state-dependent, influenced by what your brain is doing in the moment.
Abstract
- A study was made of the effects of mental arithmetic, and of listening to prose, on the bradycardia produced by breath holding with and without immersion of the face in cold water.
- Bradycardia was produced in both air and water, but the response was signifi- cantly greater on face immersion. The reaction was attenuated by mental arithmetic in both air and water. In contrast external distraction by listening to prose had no effect on cardiac response.
- It was concluded that the diving reflex can be modified by higher nervous stimulation. The effect is apparently dependent on mental challenge, such as that provoked by arithmetic.