Divers, gymnasts and trapeze artists
Divers, gymnasts and trapeze artists all perform complicated ariel manouvers. How do they do this? However they do it, they are constrained by law of conservation of angular momentum. At take off, they acquire some angular momentum. By changing the shape of their bodies, the speed of their rotation can be controlled. Making themelves more compact about the axis of rotation decreases their moment of inertia (Key Point 5.12) about that axis, and hence increases their rate of spin.
In a complicated manouver tumbling move, the direction of the angular momentum vector has to be constant also. This is a physical limitation to the tumbling manouvers that are possible when diving or performing on a trapeze.