What Pilates exercise involves lying on the back and lifting legs in a rhythmic motion?

The exercise that involves lying on the back and lifting legs in a rhythmic motion is referenced in the context of the Hundred. In this exercise, the individual lies on their back with legs raised to a tabletop position or extended at a slight angle. The movement involves engaging the core while maintaining a stable pelvis, and the arms pump rhythmically while breathing in a specific pattern. The Hundred not only strengthens the abdominal muscles but also promotes coordination and endurance through the controlled movement of both the legs and the arms.

This exercise serves multiple purposes such as improving circulation, enhancing core stability, and preparing the body for more complex movements in Pilates.