腿軟
[tuĭ ruăn]
The literal meaning of '腿軟' (tuǐ ruǎn) in English would be 'weak legs.' In context, it might not be referring physically to someone whose leg strength isn't strong but rather metaphorically speaking - possibly feeling fearful leading one's knees knocking out from nervousness; or after intense effort, even just sitting still feels like a luxury - a momentary physical weakness due to overwhelming circumstances.