IK was used for when the character's feet are on the ground and FK for when they're up in the air.
Take a look at this stupendously smooth animation of Fortnite's Harley Quinn performing a complex axel jump on an ice skating rink, brought to life by Freelance 3D Animator Ali Razavi. Set up in Maya, the sequence combines both Inverse Kinematics (IK) and Forward Kinematics (FK) animation, with the former used when the character's feet are on the ground and the latter for when they're up in the air. As for the character herself, Ali employed the "harley-quinn-suicide-squad-from-fortnite" rigged model, available for free via Sketchfab.
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