## 4 Discussion
During table contact of Tsukahara vaults, we found only a slight reduction in AKE (\(-6\%\)). Therefore, height of flight is mostly generated by transforming TKE into PE, whereas the AKE necessary for performing rotational elements during the second flight phase of Tsukahara vaults must be completely generated during jump off from the board. A strong heel strike at the end of the board contact phase in combination with a fast table contact while maintaining the hyperextended body position, may allow the athletes to create the optimal AKE at the jump off from the springboard. During table contact, performing Tsukahara vaults, athletes are required to maintain the AKE despite the conversion of TKE into PE. This can be achieved with a strong push-off from the table with the front support at the end of the table contact phase. A possible consequence of greater height (and flight time) and more AKE is a better preparation for and execution of the landing, which may benefit the E-score and thus the final score [3,4,26]. In this context, we observed greater AKE (\(+6\%\)) and PE (\(+5\%\)) during the second flight phase for Yurchenko vaults than for Tsukahara vaults. This was despite similar gains in total energy (\(+9\%\)) for both vault styles during the second flight phase. This increase in total energy is due in particular to the muscular work, which is necessary to perform the somersaults and twists during the second phase of flight. This can be recognized by the fact that the energy increase is greater when more twists are executed. Consequently, it is important that the athletes perform optimal muscle work for the intended vault during the second flight phase. This can be achieved, for example, by training the twisting technique on the trampoline. Further, total energy during the second flight phase is within 1% of that at initial springboard contact for Tsukahara vaults, indicating that total energy is merely preserved, while TKE from the run-up is transformed into PE (i.e., height of flight) and rotation during the second flight phase. This may mean that a technically poor execution of take-off and push off from the springboard and table performing Tsukahara vaults can be somewhat compensated by a greater initial TKE (i.e.,run-up velocity). Nevertheless, the run-up speed cannot be increased at will. The athletes must reach an individually optimal, and therefore controllable, speed, which allows them--adapted to their physical conditions in the upper body, as well as their technical abilities when pushing off the table--to effectively convert the energy from the run-up during the board and table contact into height of flight and rotation. In contrast to Tsukahara vaults, total energy during the second flight phase of Yurchenko vaults is 10% higher than at initial springboard contact, indicating that an important increase in energy is generated (by means of the round-off and back handspring) between run-up and take-off during such vaults. Therefore, proper execution of these pre-take-off elements is crucial for generating the energy necessary for successfully performing difficult Yurchenko vaults. ### Energy Flux of Tsukahara and Yurchenko Vaults  
At initial springboard contact, the difference in TKE between simple and difficult Tsukahara vaults (+12%) is greater than between simple and difficult Yurchenko vaults (+4%). This is not surprising and has been reported previously [3; 4; 5; 7; 11]. In order to execute a proper and effective round-off in front of the springboard for Yurchenko vaults, the musculo-tendinal properties of the upper extremities, rather than solely run-up velocity, are a limiting factor [3]. Therefore, run-up velocity must sometimes be modulated to an optimal level due to technical restrictions or poor visual targeting skills in order to hit the board optimally [27]. During springboard contact of Yurchenko vaults, preserving a greater amount of AKE seems to be a crucial factor for increasing vault difficulty (10% difference between difficult and simple vaults in the current study).