## 2 Materials and Methods
### Material  
The VE was a reproduction of the athletics track of the Stade de France (Figure 1A). It was developed using the gaming engine Unity (version: 3.2.0) and projected via a wireless HMD device (model: HTC Vive Focus 3; field of view: 120\({}^{\circ}\); resolution: 2448 \(\times\) 2448 pixels per eye; refresh rate: 90 Hz; HTC Inc., Taoyuan City, Taiwan) and a laptop with a 2.2 GHz Intel Core i9 processor and NVIDIA RTX A4500 graphics card. HTC Vive trackers (<1 mm spatial resolution, 90 Hz temporal resolution) were placed on the feet and on the head to record their position and analyze participants' motor behavior. Trackers placed on the feet also enabled virtual feet to be generated in the environment. Three lighthouse lasers were used to detect the position and orientation of the HMD and of the trackers. This virtual environment was developed for use in training by the French relay team. It is not intended for personal use.  
During the experiment, the virtual task was performed in a closed room with enough space for the participants to run 15 m. When immersed in the VE, participants were standing in the starting position on the fourth lane of the virtual track, as the third runner of the team. They were waiting for the approach of their virtual partner positioned behind them, as the second runner of the team. Realistic avatars were created _via_ motion captures collected on male and female U20 athletes of the French national team using a marker-less system (Xsens MVN; Xsens Technologies B.V., Enschede, NL, The Netherlands). These avatars were fully customizable in terms of starting distance and approach speed from trial to trial. The distance between the go-mark and the participant can also be parametrized. At the onset of each trial, the avatar started running at a constant speed, and participants were instructed to initiate their run when the avatar passed over the go-mark placed in the running lane. After the first two strides of their run, participants had to decelerate and stop and could then return to their starting line to wait for a new trial. At the end of each trial, feedback depicting the timing error in milliseconds (ms) could be delivered in the VE (time between the avatar's passage over the mark and the running initiation of the participant objectified by the lift of the rear foot).  
The real-world environment (RWE) was the athletics track at the Pierre Delort stadium (Marseille). In this condition, the virtual avatar and go-mark were replaced by real ones. During the tests in the RWE, the athletes were equipped in the same way as during the tests in the VE. HTC Vive trackers were placed on the feet and head, and three lighthouse lasers detected their positions. However, the HMD was placed on the floor next to the participant instead of on their heads. At the start of each RWE trial, a VE trial was run simultaneously to ensure data recording. A photocell integrated into the data acquisition system was placed at the go-mark level and used as a reference for calculating the timingerror. The virtual condition and real condition setups functioned simultaneously in order to carry out acquisitions simultaneously in both conditions.