Achieving is not maintaining: The temporal stability of heart rate variability during a slow breathing task
This study reveals that while slow breathing successfully increases heart rate variability (HRV) to indicate parasympathetic activation, many individuals struggle to maintain this physiological stability over time, a difficulty that is significantly linked to the maladaptive emotion regulation strategy of catastrophizing.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Breathing is the most automatic thing we do, a silent rhythm that keeps us alive without a single conscious thought. Yet, it is also one of the few bodily functions we can voluntarily control, a unique bridge between our conscious mind and our involuntary nervous system. Scientists have long known that slowing down this breath can calm the body, shifting it from a state of high alert to one of rest and recovery. This shift is often measured by looking at heart rate variability, a term that describes the tiny, healthy variations in the time between heartbeats. When the body is relaxed and flexible, these gaps between beats vary more; when it is stressed or rigid, they become too uniform. For years, research has focused on whether slow breathing can successfully trigger this calm state, showing that it generally does. But a new question has emerged: just because someone can reach a calm state, does that mean they can hold onto it?
A team of researchers at Ghent University in Belgium set out to investigate this specific aspect of self-regulation. They wanted to know if the ability to achieve a relaxed physiological state is the same as the ability to maintain it over time. In their study, published in October 2026, they asked fifty-nine adults to sit quietly for five minutes to establish a baseline, and then to breathe slowly and deeply on their own for ten minutes. Crucially, no one told them exactly how fast to breathe or gave them a rhythm to follow; they had to find their own pace and stick with it. The researchers monitored the participants' heart rate variability throughout the entire session, looking not just at the average number, but at how steady that number remained from second to second.
The results confirmed what many expected: when the participants slowed their breathing, their heart rate variability increased significantly compared to the quiet baseline. This indicated that they were successfully activating their body's relaxation system. However, the story changed when the researchers looked at the stability of that calm. While the average heart rate variability went up, the rhythm was not steady for everyone. In fact, nearly seventy percent of the participants showed signs of instability during the breathing exercise. Their heart rate variability would rise and fall erratically rather than holding a smooth, steady level of calm. This was not simply a case of people being naturally jittery, because the rate of instability was much lower during the quiet baseline period. The act of trying to maintain slow breathing on one's own seemed to introduce a new kind of fluctuation that was not present when they were just sitting still.
The study then explored why some people struggled to keep this steady state while others managed it. The researchers looked at how the participants typically handled stress and emotions, asking them about their habits of thinking and coping. They found a clear link between a specific way of thinking and the ability to stay calm. Participants who tended to catastrophize—meaning they had a habit of imagining the worst possible outcomes and exaggerating the severity of negative events—were significantly more likely to experience instability in their heart rate variability. In contrast, those who used more balanced thinking strategies or had higher resilience did not show a statistically significant difference in stability after the researchers accounted for the number of comparisons made. This suggests that the mental habit of spiraling into worst-case scenarios might interfere with the body's ability to hold onto a state of relaxation, even when the person is actively trying to breathe slowly.
These findings offer a more nuanced view of how we regulate our bodies. It appears that reaching a state of calm and staying there are two different challenges. While most people can successfully slow their breathing to trigger a relaxation response, maintaining that response without external guidance requires a level of mental steadiness that many find difficult. The study suggests that the mind's tendency to worry or exaggerate threats can disrupt the physical rhythm of the body, causing the calm to waver. This does not mean slow breathing is ineffective, but it highlights that the journey to a stable, relaxed state involves more than just changing the breathing pattern; it also involves the mental landscape in which that breathing takes place. For those seeking to use breathing exercises for stress relief, the work implies that learning to manage one's thoughts might be just as important as learning to control one's breath.
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