March 28, 2025, 3:46 pm | Read time: 5 minutes
People can build emotional connections with horses. This is why the animals are also used in animal-assisted therapy. A study has now investigated the physical effect this has on humans and animals for the first time and found astonishing patterns of heart synchronization between humans, horses, and therapists.
In equine-assisted psychotherapy, the main focus is on contact between humans and horses. This interaction has been well-documented to have a positive effect on mental health. A research team from the University of Vienna wondered whether this also triggers physiological interactions in humans and horses. The study was the first to examine the cardiac activity and stress hormone levels of the client, therapist, and therapy horse together during equine-assisted therapy (EAT).
The central question was whether there is a measurable synchronization between the participants and how the relationship influences these processes. The study was published in the journal Applied Animal Behavior Science. PETBOOK provides a summary of the most intriguing findings.
Interaction with Animals Can Influence Emotional States
Equine-assisted psychotherapy is regarded as a promising complementary approach to treating individuals with mental impairments. A central therapeutic goal is the reduction of stress. Studies have already shown that contact with animals can enhance the therapeutic effect.1
Horses excel at non-verbal communication, offering an advantage for individuals with limited language abilities. Interaction with animals can also influence emotional states and change physiological processes such as heart rate and hormone levels. Synchronization, which is the alignment of bodily processes such as the heartbeat, plays a pivotal role in social relationships.
Some studies have already shown that such synchronization can occur in human-animal interactions. For example, Finnish researchers were able to prove that the variability of our heart rate synchronizes with that of dogs (and vice versa) when we spend time together with our four-legged friends (PETBOOK reported). The current Austrian study aimed to determine whether and under what conditions such processes also occur during human-horse interactions.
Researchers Examined Heart Rate and Stress Hormones During Equine-Assisted Therapy
The researchers examined ten young women with mental disabilities who had many years of experience with equine-assisted psychotherapy. They took part in four standardized therapy sessions — two with horses and two without. They measured the following parameters in the client, therapist, and horse before, during, and after the session:
- heart rate (HR),
- heart rate variability (HRV) and
- the cortisol level (a stress hormone).
Only Five Clients Worked with a Familiar Horse
The horses that participated in the study were four Criollos. This is a breed of horse that originated in Argentina and is mostly used as a riding and western horse. Criollos are known for their calm demeanor, willingness to cooperate with humans, and friendly nature with a pleasant temperament.
As the study also wanted to take into account the emotional bond between horse and human, five clients worked with their favorite horse, with whom they had an established relationship. The five other clients were given a randomly assigned animal. All sessions followed a fixed schedule with relaxation, stress, and rest phases. The data was recorded using chest straps and saliva samples and statistically analyzed.
Synchronization Depends on the Relationship Between Humans and Horses
Across all session phases, there was no significant change in heart rate, heart rate variability, or cortisol levels in the clients — neither in comparison to the control condition nor over time. One exception: during the exercise phase — riding through an obstacle course — the clients’ heart rate was significantly lower when they rode a real horse compared to the control group who did not interact with horses. HRV parameters and cortisol, on the other hand, did not differ between the conditions.
The findings regarding heart rate synchronization were remarkable: this correlated not only between therapist and client but also between humans and horses. The synchronization of the heart rate between the therapist and the horse was even more pronounced than that between the therapist and the client, especially when it was a familiar horse. In contrast, there was only a correlation in heart rate between the client and the horse if the horse was familiar to her, but not with unfamiliar animals. The synchronization was, therefore, strongly dependent on the relationship between the human and the horse.
Study Provides Initial Indications
The study provides initial evidence that heart rate synchronization occurs during equine-assisted psychotherapy. This is especially true when a close relationship exists between the human and the horse. This applies to both the client and the therapist. This synchronization of heart rhythms is associated with emotional harmony, bonding, and stress reduction. It is considered to be a central mechanism of social interaction.
Nevertheless, the pilot study does not provide any generally valid statements but rather initial indications. The number of participants (ten clients, four horses, and one therapist) was limited, which restricts the validity of the findings. The influence of the familiar environment could also have distorted the results. This is because the control condition also took place in the riding stable, which could have had a calming effect on the clients. After all, the stable was an emotionally positive place for them. In addition, the study took place in winter, which can influence physiological processes.
Further research with larger samples and new measurement methods, such as the bonding hormone oxytocin, is urgently needed to better understand the importance of the human-animal relationship in equine-assisted therapy.
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The Bond Between Humans and Horses Is Crucial
Nevertheless, the study is remarkable in its methodological consistency: for the first time, physiological data of all three actors — client, therapist, and horse — were recorded simultaneously. This allows new insights into the complex network of relationships in animal-assisted therapy.
The results prove how important the connection between humans and horses is. It is evident that simply having an animal present is insufficient to elicit physiological effects; rather, it is the established bond that is significant. This is in line with the theory of the “One Health” approach, which emphasizes the close connection between humans, animals and the environment. The study shows: Relationship not only has an emotional effect, but also a physiological one – right down to the heartbeat.