## 2 Materials and Methods  
### Sample Characterization  
This investigation included base and top gymnasts from first division and elite level, competing at national and international level, with a minimal weekly training volume of 30 h. Twenty-one gymnasts (12 bases and 9 top gymnasts) volunteered to participate in this investigation.  
The 12 base gymnasts included 8 females (age: 18.00 (3.12) (median interquartile range)) years, height: 1.64 (0.05) m, mass: 64.75 (7.56) kg and training experience: 8.00 (5.00) years) and 4 males (age: 16.50 (1.29) years, height: 1.71 (0.03) m, mass: 65.40 (6.07) kg and training experience: 5.00 (4.00) years). The 9 top gymnasts included 7 females (age: 13.14 (2.80) years, height: 1.45 (0.04) m, mass: 34.56 (3.73) kg and training experience: 6.00 (1.00) years) and 2 males (age: 13.00 (1.41) years, height: 1.43 (0.17) m, mass: 39.80 (9.48) kg and training experience: 9.50 (5.00) years).  
Participants were grouped in 12 pairs of ACRO (8 female pairs, 1 mixed pair, and 3 male pairs), where 3 top gymnasts were grouped with 2 different bases to increase the number of pairs. The 12 pairs were further divided into two groups, using the median of the experience of training together as a pair (3 months) as the grouping criteria. Accordingly, 7 pairs were classified as less experienced (LE), with a maximum of 3 months of training together, and 5 pairs were included in the more experienced (ME) group, corresponding to a minimum of one year of training together. Detailed information about the groups is provided in Table 1.  
All participants, or their legal guardians, after being informed of the study's purpose, procedures, benefits, and risks, gave their voluntary and informed consent to participate, in accordance with the Declaration of Helsinki and the research Ethics Committee of the Faculty of Sport of the University of Porto (CEFADE 02.2022, approved on 18 January 2022).  
Gymnasts completed their usual warm-up and were given a free performance volume of \(\sim\)15 min to adapt to the laboratory environment. Each pair performed 10 vertical throws, with 2-3 min of rest between each attempt. Data collection was performed using a set of 8 Miqus video cameras (Qualisys AB, Gothenburg, Sweden) operating at 85 frames per  
\begin{table}
\begin{tabular}{c c c c c} \hline  & \multicolumn{2}{c}{**LE (N = 7)**} & \multicolumn{2}{c}{**ME (N = 5)**} \\ \hline
**Variables** & **Base** & **Top** & **Base** & **Top** \\ \hline Age (years) & 18.00 (7.00) & 14.00 (5.00) & 16.00 (0.00) & 12.00 (1.00) \\ Mass (kg) & 70.10 (15.60) & 36.40 (9.20) & 61.10 (5.40) & 32.80 (0.10) \\ Height (m) & 1.68 (0.07) & 1.49 (0.10) & 1.64 (0.09) & 1.45 (0.05) \\ Experience as a pair (years) & 0.25 (0.17) & & 2.00 (1.75) \\ \hline \end{tabular} Note: Values reported as median (interquartile range).  
\end{table}
Table 1: Characterization of the less experienced (LE) and more experienced (ME) groups.  
second, which allowed for the use of the higher resolution option (1920 \(\times\) 1080 pixel). The capture volume encompassed the pair, as well as the top's flight path, and was calibrated using a wand. The maximum acceptable error for calibration was established as 0.80 mm. A 2 \(\times\) 3 m gymnastics mat was placed adjacent to the base's standing position as a safety measure against falls.  
The gymnastic' movement was processed using Markerless analysis software, v2023.1.0.3160.p14 (Theia Markerless, Inc., Kingston, ON, Canada) and the resulting 6 degrees of freedom models were exported to Visual3D, v2023.06.3 (C-Motion, Inc., Germantown, MD, USA) for further analysis. This included the calculation of the position and velocity of the center of mass (CoM) of the base and top gymnastics in relation to the laboratory's global coordinate system (GCS). We also underline that this work focuses on the vertical axis (z), as the assessed skill occurs essentially in this axis.