Which feature requires that skaters participate in each element shape?

The feature that requires skaters to participate in each element shape is the one that focuses on the transitions between different configurations or formations during a synchro skating performance. In this case, change of element shape specifically pertains to the requirement that all skaters must be actively involved in executing each shape as it is formed throughout the course of the routine.

This feature ensures that there is a cohesive effort and representation of the element throughout the entire team, highlighting the collective skills of all skaters in adapting to variations in formation shapes. By requiring full participation in every shape, it allows judges to evaluate how well the team executes transitions and maintains synchronization while performing.

Other options, while related to synchro skating, do not specifically emphasize the necessity for participation in each shape at the same level as change of element shape. The focus on active involvement enriches the visual and technical aspects of the performance, which is essential for scoring in synchro skating competitions.