Go look at the elf videos posted on the site. Mobility and movement of joints are closely related.
Most people who lack “mobility” just lack an awareness of where that joint can be taken. You’ve got to steer somewhere before you load the joint, so start with just moving.
Ankle circles accessing those ranges are great. Isolate them solely to the ankle and ankle only. Foot work can help a lot. Calf / tibialis work can also be great.
Overall a steady diet of moving that joint and strength of its end ranges is your best bet.
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