## 4 Discussion
### Energy Flux of Tsukahara and Yurchenko Vaults  
Our results for Tsukahara vaults show that TKE makes up almost three quarters (72%) of total energy at initial springboard contact, thus confirming previous investigations and emphasizing importance of a high run-up velocity for performing difficult vaults. For Yurchenko vaults, however, TKE at initial springboard contact is 37% lower on average, comprising only about half (49%) of total energy. On the other hand, the characteristic round-off in front of the springboard for Yurchenko vaults generates a substantial amount of AKE (25% of total energy), which nonetheless enables gymnasts to perform vaults of similar difficulty as with the Tsukahara style. It should be noted, however, that the sufficient AKE is generated only by a technically correct round-off. For Tsukahara vaults, total energy is more or less preserved (\(-\)2%) across the springboard contact phase. During this phase however, TKE decreases (\(-\)26%) as it is mainly transformed into AKE (+70%) and PE (+23%). Consequently, it can be concluded that gymnasts generate most of the AKE necessary to perform Tsukahara vaults during springboard contact. This is contrary to the findings of [PERSON], [PERSON], [PERSON], and [PERSON] [11], who reported a large increase in AKE during the first flight phase. In contrast to Tsukahara vaults, we found an increase (+8%) in total energy during springboard contact for Yurchenko vaults. This can mainly be attributed to an increase in PE (+27%), whereas TKE (\(-\)0.3%) and AKE (\(-\)4%) remain fairly stable. Our results are in agreement with [PERSON] et al. [20], who observed a preservation of horizontal velocity and an increase in vertical velocity during jump off from the springboard of Yurchenko vaults. Obviously, athletes generate sufficient TKE and AKE with the run-up and round-off in front of the springboard so that translation and rotation must merely be preserved across the springboard contact phase. Hence, the total energy increase during springboard contact may be generated by an effective and powerful jump off. A powerful springboard jump off is realized through a combination of the gymnast's actions and the interaction with the elastic properties of the board and can be better described as a tension-shortening cycle instead of a stretch-shortening cycle. Nevertheless, a jump off from a springboard is closely related to muscle stiffness, and most importantly a high level of reactive strength [20, 21, 22], i.e., the ability to generate high ground reaction forces within a short contact time. This relationship emphasizes the importance of physical conditioning for performing difficult vaults. Interestingly, during table contact, total energy decreases similarly for [PERSON] (\(-6\%\)) and Yurchenko vaults (\(-7\%\)), even though the push off is executed in a completely different position ([PERSON]: two-handed from a backwards handspring; Tsukahara: mainly one-handed sideways from a round off). According to [PERSON] et al. [23], two-handed push offs (forward handspring) may evoke 2.5 times greater push-off forces than Tsukahara push-offs. Therefore, it seems feasible that either elastic or non-elastic properties of the vaulting table, as well as locomotor properties of the upper body muscles and tendons [24] inhibit a total energy conservation during table contact. During table contact of Yurchenko vaults, AKE is drastically reduced (\(-30\%\)). The fact that this is achieved with a backwards handspring, and that athletes see the table only shortly before push off, may emphasize the high technical and mental demands of these vaults [3]. Additionally, this corresponds quite expectedly to the intention of the preliminary round-off characterizing this vaulting style, namely, to generate a large amount of AKE, which can subsequently be transformed into PE (height of flight), as was also overserved in the current study. In this context, [PERSON] [25] observed reductions in angular momentum at push off for Yurchenko vaults between 5% to 20%.