You can picture contortion as something being twisted hard out of the shape it should have: a back folded much further than a back should fold, a face screwed up tight, a metal bar bent past straight. The word keeps that same picture even when nothing physical is being twisted at all.
From the word’s history
The Wiktionary etymology tree traces contortion to Latin contortus, from con- plus torqueo (to twist), which went into Middle French contortion and then English. The Latin root is literally a twisting, which is the same picture the modern word still carries.
Wiktionary 的詞源樹把 contortion 追到拉丁文 contortus：con- 加上 torqueō（扭、轉），再經中古法文 contortion 進入英文。這個根本來就是「扭」，跟今天這個字給人的畫面剛好同一個。
Wiktionary entry for 'contortion' (kaikki:3f6f69a190036ae4:1054200239:16594), etymology tree: Latin con- + torqueō > contortus > contortiō > Middle French contortion
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