thih-kut-siⁿ鐵骨生

thin but strong and sturdy

thin but strong and sturdy (of someone's body)

English Wiktionary, “鐵骨生” (CC BY-SA 4.0) — https://en.wiktionary.org/wiki/%E9%90%B5%E9%AA%A8%E7%94%9F · confidence: Medium (Wiktionary)