Something fascinating happens every time we interact with another person in a meaningful way: Several of our biological signals start to synchronize. This has been shown for various brain waves and body parameters, such as heart rate variability (HRV).
The latter is particularly interesting in the context of stress research. It has been shown in several studies that a higher high-frequency HRV is linked to better stress resilience and better ability to relax. In contrast, a lower high-frequency HRV has been linked to worse stress resilience and problems relaxing.
What is largely unclear, however, is to what extent the synchronization of heart rate variability in two people is linked to stress experience and resilience. This could, however, be really interesting for getting a better understanding of what stress does to relationships and why some couples have bigger issues than others when dealing with stressful situations.
A New Study on Partner Stress and Heart Rate Synchronization
A new study, published by me and my co-authors in the scientific journal Biological Psychology (Denk et al, 2026), focused on investigating the effects of partner stress on heart rate synchronization. Entitled “Coupled Hearts—Effect of Partner Stress on Cardiac Synchronization,” our research team, led by scientist Bernadette F. Denk from the University of Konstanz in Germany, investigated the effects of stress on heart rate synchronization in 75 romantic couples.
The couples were tested in two groups. In one group, one partner underwent the so-called socially evaluated cold pressor task, an established psychological paradigm to induce stress. In this task, the person has to put their non-dominant hand in a box with ice-cold water for up to three minutes. During this time, they are recorded by a camera pointing at their face, and a scientist takes notes on their behavior. This task has been shown to robustly induce a stress response in people. The other partner had to perform a non-stressful control task.
In the second group of couples, both partners performed the non-stressful task, and no one was stressed. In both groups, both partners performed these tasks individually and were subsequently reunited.
Together, they then performed three different tasks. First, the couples performed a non-verbal synchronization task, in which they were asked not to speak to each other but to imagine how the other person was feeling. Second, the couples performed a walking task in which they were asked to walk together in synchrony for 10 minutes and hug occasionally.
The last task was an unstructured social interaction in which couples were asked to sit down and talk about whatever topic they wanted to discuss. During all three tasks, the heart rate variability of partners was measured continuously.
One Partner’s Stress Negatively Impacts a Couple’s Heart Rate Synchrony
The results of the study were quite striking: In all three tasks, the heart rate synchrony was lower in the group in which one partner was stressed compared to the group in which both partners were not stressed. This suggests that even if only one partner is stressed out, the experience of stress massively disrupts heart rate synchronization in couples.
It is a common experience in couples that the relationship can suffer when one partner experiences a high level of stress. The study further strengthens the idea that the negative impact of stress, not just on individuals but on relationships, has a biological basis.