## 4 Discussion

Table 3: Cross-correlation results between the curves from the top global coordinate system (GCS) and base, and between the base and top local coordinate system (LCS) of less experienced (LE) and more experienced (ME) pairs. Indexes of cross-correlation (r) are presented for the maximal cross-correlation (r\({}_{\text{max}}\)) and for lag = 0 (r\({}_{0}\)) of position and velocity. may represent a preparatory mechanism for coping with the aerial phase. In parallel, [PERSON] and [PERSON] [43] reported that proper timing during take-off allowed to cope with moderate perturbations of the approach characteristics, and that elite performance also requires in-flight adjustments [44]. For assessing the individual contribution of each gymnast, the use of the GCS reveals the movement performed by the base but does not reveal the movement that the top performs on its own, without the influence of the base. The top LCS measurement provides coaches and researchers with insightful information about this gymnast's motion. Coaches must learn to observe the system, examining the base actions, but also understanding the top's own ability to generate impulse or to allow the base gymnast to generate it. Similarly, in collective load carriage, one participant also made greater efforts than the other as a coordination strategy [16]. Thus, the use of the LCS confirmed that tops present limited independent movement and are primarily influenced by the base's motion. Regarding the experience level, ME tops LCS present a higher TO Pos, which could suggest higher participation over experience, and ME tops GCS and LCS achieved lower MU Vel, indicating higher efficiency (only using the necessary velocity to conduct the aerial phase). Studies should focus on evaluating this tendency in distinct gymnastics skills. When comparing spatial-temporal variables across experience levels, ME pairs were faster in the entire task and Phase I (downward movement), as expected, since higher training experience in gymnastics, shorter contact times, and faster movement are associated [25; 26; 27; 28; 45]. ME gymnasts performed Phase I faster, probably because they require less time to coordinate their downward actions, compared to LE. Possibly, they have also developed stronger eccentric braking. This mechanism demands a great volume of specific training to start to predict, control, and accommodate [46]. In Phase II, only ME bases and systems were faster, likely because ME bases are stronger and faster in the upward movement, and the major contributors to the system behavior, as seen previously. Studies have investigated the balance [47] and the jumping skills [16; 48] of base and top gymnasts; however, the inclusion of different experience levels is recommended for a more accurate characterization. When the entire trial is considered, different experience levels distribute the same amount of relative time differently. ME gymnasts spend significantly higher relative time in Phase II, when compared to LE, possibly because they are better coordinated, and may prioritize vertical displacement by actively extending the duration of upward motion. This could also be a strategy used to improve energy transfer from the top to the base gymnast, including the application of [PERSON]'s biomechanical principle of the temporal coordination of partial impulses [49]. In horse riding, riders also adapt temporally and spatially to the horse's trunk movement to achieve and keep a well-adjusted seat [31]. Coaches and researchers should be aware that ACRO pairs spent more relative time in Phase I (around 60%) and less in Phase II (around 40%), regardless of the experience level, but a higher experience allows for a shorter downward movement and longer upward motion. In spatial variables, a lower MD Pos was found for the ME tops GCS, LCS, and systems, but a higher TO Pos was found only for ME tops LCS. It is possible that ME tops can use a higher range of motion, but only ME tops LCS achieve higher TO Pos.