Experimental conditions and control condition

In both relaxation intervention conditions, i.e., with and without verbal suggestions, participants were provided with two brief relaxation exercises and participants were told that they would perform two relaxation exercises with a short break in between the exercises. Participants were instructed to sit upright in their chair with their feet on the ground and their arms resting on their thighs or on the seat rests. Subsequently, the experimenter provided the participant with Sennheiser HD201headphones and instructed them to start the audio file when they were ready to listen to the relaxation exercises. The experimenter then left the room. The first relaxation exercise focused on progressive muscle relaxation and led participants through a series of practices to tense and relax various muscle groups throughout the whole body. This relaxation exercise took around 16 minutes. Thirty seconds after the end of the first exercise, the second visual imagery-based relaxation exercise automatically started, which was focused on visualization of optimal health. Participants had to visualize that they were feeling healthy and full of energy, and that their body was in an optimal condition. This intervention took around 5 minutes. Total duration of the relaxation intervention was 20–25 minutes.

The verbal suggestions focused on the effectiveness of the relaxation intervention in performing the follow-up challenge test with the aim to facilitate more positive outcome expectancies for this task and yielded some cues for better performance on this task. More specifically, the experimenter provided participants with the following verbal suggestions (translated from Dutch):

“In a moment, you will complete some tasks, including an arithmetic task. Prior research has shown that you can complete those tasks better when you relax by:

Sitting as restful and relaxed as possible;

Keeping in mind that your respiration has to be restful and regular, calm and relaxed.

It is important that you keep this information in mind. You need this information in order to perform well on the tasks. Therefore, be careful not to forget these instructions.”

In the brief relaxation intervention plus verbal suggestions condition, participants were first provided with the verbal suggestions followed by the relaxation intervention. In the verbal suggestions only condition, participants did not receive the relaxation exercises, but were exposed to the stress task directly after receiving the verbal suggestions.

In the control condition, participants completed several neutral word finding puzzles for 25 minutes before they were exposed to the TSST.