A new study in Germany found that men who performed 3 minutes of a physically demanding exercise had more intense reactions to pictures with sexual contents compared to a control group. However, responses to non-sexual pictures were not affected. The study was published in Psychophysiology.
Studies in the past century have indicated that our emotional reactions can transfer between situations. The same happens with physiological arousal. This then results in wrongfully attributing the emotions caused by previous events to situations and events that did not cause them.
A situation where a person that became happy by some fortunate turn of events, continues feeling happiness and attributing happy feelings to other events that day is something well-known from everyday experience. Similarly, a person that was made angry by interaction with one person may act less positively than usual to people he/she encounters immediately after.
Researchers link these characteristics of human emotional reactions to the increased activity of the sympathetic nervous system. The sympathetic nervous system is a part of our autonomic nervous system that regulates our “fight-or-flight” responses. It is activated in times of stress, threat, or arousal. When the sympathetic nervous system is activated, it increases heart rate, dilates blood vessels, raises blood pressure, and releases stress hormones like adrenaline, preparing the body for intense physical activity or emergency situations.
Study author Johannes B. Finke and his colleagues were interested in testing recent findings that physical exercise makes men more responsive to sexual stimuli. They wanted to know how physiological responses to sexual stimuli (e.g., pictures with sexual content) might be different after physical exertion.
The researchers organized a study that included 45 male students of the University of Trier and the University of Applied Sciences Trier in Germany. The participants were paid 20 EUR each for participation. To participate in the study, students were required to have a body mass index between 18 and 30 i.e., not be underweight or obese, to have no psychiatric or chronic illnesses, to not be excessive smokers or drug users. They were also required not to be exercising for more than 8 hours a week or work in night shifts.
Participants were randomly assigned to one of the two groups – the stress (i.e., physical exercise) group or the control group. At the start of the experiment, a researchers would have a participant sit in a comfortable chair and attach equipment for measuring heart rate, blood pressure, and other physiological responses.
Participants would rest for 5 minutes and then undergo a grip strength test i.e., they were asked to grip a testing device in their hands as strongly as they can. Another 10-minute rest followed after which participants rated their subjective stress, arousal, and anxiety on a scale on a screen.
After this, participants performed an isometric handgrip strength task i.e., they were asked to grip the measurement device and keep the pressure for 3 minutes. The stress group was asked to apply 45% of their maximum grip strength for this period (i.e., apply strong pressure), while the control group was asked to grip it with 10% of their maximum grip strength (i.e., apply very weak pressure). After this procedure and a 7 minutes rest, they were shown pictures.
Pictures were organized into groups – pictures showing violence/threat, sport activities, erotic couples, everyday social situations, or nature landscapes. Presentation was organized in blocks in a way that would minimize interference between different categories of pictures.
The researchers used the “nature” pictures as a reference point to assess reactions to other types of pictures. To make sure that participants paid equal attention to all pictures, researchers gave them a task to press a button whenever they saw two pictures belonging to the same category in succession.
The researchers collected data on participants’ startle eyeblink responses using an eye tracking device. These responses were induced by loud white noise played via headphones for half a second. They also collected data on blood pressure, heart rate changes (electrocardiograms), activities of different muscles (electromyograms), pupil diameter (via the eye tracker), and skin conductance.
Results showed that the stress condition led to a higher heart rate than the control. Participants also rated the stress condition as more stressful. Participants had enhanced skin conductance responses when viewing sexual pictures and pictures of violence compared to reactions to pictures of nature.
Comparing the two groups, results showed that startle responses and skin conductance to emotional pictures were not affected by previous stress treatment. Heart rate changes and pupil responses were enhanced in the stress group compared to the control. In simple terms, being asked to strongly grip the measuring device and hold it for 3 minutes led to increased heart rate and changes in pupil responses when viewing sexual pictures later, compared to the group that was gripping the measuring device only lightly.
“Taken together, our findings provide strong evidence for enhancement of sexual processing by acute stress exposure in men and suggest differential involvement of parasympathetic versus sympathetic mechanisms,” the study authors concluded.
It should be emphasized that these effects of acute stress are quite contrary to the effects severe and/or chronic stress have on sexual and reproductive functions.
The paper makes a valuable contribution to the scientific understanding of physiological responses to sexual stimuli. However, it also has limitations that need to be taken into account. Notably, the stimuli used were pictures, shown in a situation where participants were induced to pay equal attention to them. Also, all participants were young. Results in more naturalistic situations and on different age group might not be the same.
The study, “Increased pupil and heart-rate responses to sexual stimuli in men after physical exertion“, was authored by Johannes B. Finke, Sebastian Hahn, Hartmut Schächinger, and Tim Klucken.