Abdominals, Hip Flexors
Obliques, Core
Watch Tutorial
https://www.youtube.com/shorts/wrY3lORfPek
https://www.youtube.com/shorts/MxsRi8dtzmU
Hang from bar.
Engage core.
Quickly drive right knee to chest.
Lower right knee while driving left knee up.
Continue alternating rapidly.
Avoid swinging.