## 2 Materials and Methods
### Dataset Collection Protocol  
The MMD-MSD dataset was recorded in a single 45 min session per participant, with short breaks between the data collection episodes. The data collection protocol aimed at the acquisition of motion data, pictures, videos, and physiological signals. We used a common data acquisition workflow (cf. Figure 2) implemented for each of the 100 volunteers who were recruited as participants in the data collection campaign. None of the volunteers reported previous experience with an ergonomics-oriented data collection campaign, and nobody had previous exposure to the Stroop test. Figure 1: Typical body postures registered during the subsequent steps of the data collection process: (a) regular standing en face (front-on view); (b) regular profile (left side view); (c) corrected standing en face (front-on view); (d) corrected profile (left side view); (e) regular sitting posture; (f) corrected sitting posture; (g) active sitting posture with air-cushioned stability disk. Each participant was admitted individually to the premises of the laboratory, accompanied only by the team specified above, who were directly involved in implementing the data collection process. Access to the laboratory by other people was restricted to lower the degree of discomfort and distraction during the data acquisition. Timestamp synchronization between all recording channels was implemented through a universal marker event, which was generated by the software tool at the beginning and the end of each data collection step. As shown in Figure 2, the data collection started with a briefing about the data collection process, filling in a consent declaration, and the entry questionnaire. The questionnaire collected general demographic information about the volunteers, their activity/sport/sleep habits, and self-reported pain issues, which were later used as self-assessment tags. After the entry questionnaire, each participant was invited to stand next to the wall with grid wallpaper, and photographs were taken in spontaneous and corrected standing positions. Pictures were taken of each person standing _en face_ (front-on view) and profile (left side view) (cf. Figure 1), including spontaneous and corrected posture. The spontaneous standing posture for each participant corresponds to the uncorrected comfortable position that the participant took naturally, while the corrected ones refer to the positions after the professional physiotherapist manually adjusted the body posture of each person according to the established MSD prevention recommendations. Next, the participant was asked to sit on an office chair next to the office desk with a computer configuration and perform several tasks using the computer. The technical assistant helped each participant to put on the Empatica E4 wristband. The recording sessions began with a baseline recording, and each participant was instructed on how to perform the Stroop test. This corresponds to the start of the core part of the data collection, beginning with the initial baseline recording of physiological signals and finishing with the end of the second Stroop test. These data collection steps were registered from an overhead perspective using a video camera. The video recordings captured each participant's positions and sitting behavior during the implementation of the assigned computer-bound tasks. All participants in the experiment were asked to complete the Stroop test twice--sitting on a chair in their usual comfortable work posture, and sitting on a stability disk placed on the chair. When performing Stroop Test #1, each participant was sitting in an office chair in their usual working position with a computer. While working on Stroop Test #1, a picture of their spontaneous sitting posture was taken from the perspective of the left profile. At some point, the medical doctor corrected the sitting posture of the participant to correspond to the ergonomic body position, and then another picture was taken.