## 2 Materials and Methods
### Measurement Setup and Protocol  
The spatiotemporal, kinematic, and kinetic parameters of both perturbed and unperturbed gait were recorded using the Interactive Real-Time Gait Analysis Laboratory (GRAIL, Motek Medical B.V., Amsterdam, The Netherlands). The GRAIL system includes an instrumented treadmill with dual split belts (1000 Hz), a ceiling-suspended safety harness, a motion capture system (Vicon Metrics Ltd., Oxford, UK) operating at 100 Hz, three video cameras, and synchronized virtual reality environments projected onto a 180\({}^{\circ}\) circular screen (5 m in diameter, 3 m in height, using three projectors).  
At the start of the study, participants' anthropometric data were collected. The Human Body Model 2 (HBM2) was then applied with 25 reflective markers to track movement (Figure 1). The D-Flow software (3.26, Motek Medical B.V., Amsterdam, The Netherlands) was used for model adjustments, perturbation control, and data collection.  
Participants wore comfortable sports shoes and walked on the treadmill at a constant speed of 1.2 m/s for approximately 80 s. Perturbations were triggered using the D-Flow software and applied unexpectedly to the left treadmill belt during the toe-off (pre-swing) phase [24]. These perturbations occurred around the 30 th, 40 th, 50 th, 60 th, and 70 th seconds during the trial (Figure 2). The perturbations were designed to simulate a \"trip-like\" effect by slowing the left belt, causing the standing foot to slide backward. The magnitude of the perturbation was rated as 5 on a scale from 1 to 5, corresponding to a change in belt speed  
Figure 1: The front, side, and rear views of the marker configuration used in the Human Body Model are presented. The green markers indicate the anatomical reference points used to define the skeleton during the initialization process, as follows: XYPH—the sixphoid process of the sternum, LASIS and RASIS—the left and right anterior superior iliac spine, LPSIS and RPSIS—the left and right posterior superior iliac spine, LGTRO and RGTRO—the left and right greater trochanter, LLEK and RLEK—the left and right lateral epicondyles of the knee, LLM and RLM—the left and right lateral malleolus of the ankle, LMT5 and RMTS—the left and right fifth metatarsal, LTOE and RTOE—the tips of the left and right toes, LHEE and RHEE—the left and right heels. Additional markers, which are technical markers providing redundancy and robustness for the model, included the following: STRN—the jugular notch of the sternum, NAVE—the navel, T10—the 10 th thoracic verteba, SACR—located midway between the LPSIS and RPSIS points, FLTHI and FRTHI—the left and right lateral thigh (positioned halfway between the greater trochanter and the lateral knee epicondyle), LATI and RATI—the left and right lateral shank (placed halfway between the lateral knee epicondyle and the lateral malleolus).  
of approximately 0.5-0.6 m/s. During these events, the speed of the left belt was reduced to \(\sim\)0.6 m/s (Figure 2), with the perturbation lasting \(\sim\)0.93 s. This methodology aligns with the approach described by [PERSON], et al. [25]. It is worth noting that the presented research is part of a large research project, where respondents were subjected to other perturbations [26].