Oh man, we are almost done, stay with me though if you're a skater because these are two key skating movements that you might not be thinking about.
What movements happen at this joint?
Inversion is when you lift the inner edge of your foot, not at the ankle joint, but at the subaltar joint below the ankle joint, and eversion is when you lift the outer edge of your foot. Technically this is a foot joint and movement, but functionally you still probably think of it as your ankle.
I assume that the book includes inversion and eversion because they're functional to a lot of activities. I can tell you that they're hella functional to skating, there's bending your ankles and then there's more. When Papa Doc tells you to spell out the alphabet with your feet, that's to work all of your ankle movements and muscles. You need to invert and evert your feet to get at your angles and edges, which is what makes just plain speed happen, for starters, and also swizzles, plow stops, slaloms, hockey stops... work those ankles, ladies!
What muscles make these movements happen?
The muscles that invert your foot at the subaltar joint are your anterior tibialis and extensor hallucis longus and your posterior tibialis, flexor hallucis longus and flexor digitorum longus. I don't really understand that mix of extensor and flexors and it slightly offends my sense of order, but so it is.
The muscles that evert your foot at the subaltar joint are your extensor digitorum longus and peroneus tertius and your peroneus brevis and peroneus longus.
What exercises make these muscles work?
Resisted inversion and resisted eversion with resistance bands basically works these movements and muscles with added dorsiflexion and plantarflexion, if the muscle in question is also a dorsiflexor or plantarflexor.
I just had an idea, resisted alphabet... yeah?